schala/schala-lang/language/src/parsing.rs

//! # Parsing
//! This module is where the recursive-descent parsing methods live.
//!
//!
//! # Schala EBNF Grammar 
//! This document is the authoritative grammar of Schala, represented in something approximating
//! Extended Backus-Naur form. Terminal productions are in "double quotes", or UPPERCASE
//! if they represent a class of tokens rather than an specific string, or are otherwise
//! unreprsentable in ASCII.
//!
//! ## Top level structure
//!
//! ```
//! program := (statement delimiter)* EOF
//! delimiter := NEWLINE | ";"
//! statement := expression | declaration
//! block := "{" (statement delimiter)* "}"
//! declaration := type_declaration | func_declaration | binding_declaration | impl_declaration
//! ```
//! ## Declarations
//!
//! ### Types
//! ```
//! type_declaration := "type" type_declaration_body
//! type_declaration_body := "alias" type_alias | "mut"? type_singleton_name "=" type_body
//! type_alias := IDENTIFIER "=" type_name
//! type_body := variant_specifier ("|" variant_specifier)*
//! variant_specifier := IDENTIFIER | IDENTIFIER "{" typed_identifier_list "}" | IDENTIFIER "(" type_name* ")"
//! typed_identifier_list := typed_identifier*
//! typed_identifier := IDENTIFIER type_anno
//! ```
//! ### Functions
//!
//! ```
//! func_declaration := func_signature func_body
//! func_body := ε | nonempty_func_body
//! nonempty_func_body := "{" (statement delimiter)* "}"
//! func_signature := "fn" func_name formal_param_list type_anno+
//! func_name := IDENTIFIER | operator
//! formal_param_list := "(" (formal_param ",")* ")"
//! formal_param := IDENTIFIER type_anno+
//! ```
//!
//! ### Variable bindings
//! ```binding_declaration := "let" "mut"? IDENTIFIER "=" expresion```
//!
//! ### Interfaces
//!
//! ```
//! interface_declaration := "interface" type_singleton_name signature_block
//! impl_declaration := "impl" type_singleton_name decl_block | "impl" type_singleton_name "for" type_name decl_block
//! decl_block := "{" (func_declaration)* "}"
//! signature_block := "{" (func_signature)* "}"
//! ```
//!
//! ### Type Annotations
//!
//! ```
//! type_anno := ":" type_name
//! type_name := type_singleton_name | "(" type_names ")"
//! type_names := ε | type_name (, type_name)*
//! type_singleton_name = IDENTIFIER (type_params)*
//! type_params := "<" type_name (, type_name)* ">"
//! ```
//!
//! ## Expressions
//! ```
//! expression := precedence_expr type_anno+
//! precedence_expr := prefix_expr
//! prefix_expr := prefix_op call_expr
//! prefix_op := "+" | "-" | "!" | "~"
//! call_expr := index_expr ( "(" invocation_list ")" )* | ε
//! invocation_list := invocation_argument ("," invocation_argument)* | ε
//! invocation_argument := expression | IDENTIFIER "=" expression | "_"
//! index_expr := primary ( "[" (expression ("," (expression)* | ε) "]" )*
//! primary := literal | paren_expr | if_expr | for_expr | while_expr | identifier_expr | lambda_expr | anonymous_struct | list_expr
//! expr_or_block := "{" (statement delimiter)* "}" | expr
//! ```
//!
//! ### Primary expressions
//!
//! ```
//! list_expr := "[" (expression, ",")* "]"
//! lambda_expr := "\\" lambda_param_list type_anno+ nonempty_func_body
//! lambda_param_list := formal_param_list |  formal_param
//! paren_expr := "(" paren_inner ")"
//! paren_inner := (expression ",")*
//! identifier_expr := named_struct | IDENTIFIER
//! ```
//!
//! ## Literals
//! ```
//! literal := "true" | "false" | number_literal | STR_LITERAL
//! named_struct := IDENTIFIER record_block
//! record_block :=  "{" (record_entry, ",")* | "}" //TODO support anonymus structs, update syntax
//! record_entry := IDENTIFIER ":" expression
//! anonymous_struct := TODO
//! number_literal := int_literal | float_literal
//! int_literal = ("0x" | "0b") digits
//! float_literal := digits ("." digits)
//! digits := (digit_group underscore*)+
//! digit_group := DIGIT+
//! ```
//!
//! ### Patterns
//! ```
//! pattern := "(" (pattern, ",")* ")" | simple_pattern
//! simple_pattern := pattern_literal | record_pattern | tuple_struct_pattern
//! pattern_literal := "true" | "false" | signed_number_literal | STR_LITERAL | IDENTIFIER
//! signed_number_literal := "-"? number_literal
//! record_pattern := IDENTIFIER "{" (record_pattern_entry, ",")* "}"
//! record_pattern_entry := IDENTIFIER | IDENTIFIER ":" Pattern
//! tuple_struct_pattern := IDENTIFIER "(" (pattern, ",")* ")"
//! ```
//!
//! ### If-expressions
//! ```
//! if_expr := "if" discriminator ("then" condititional | "is" simple_pattern_match | guard_block)
//! discriminator := precedence_expr (operator)+
//! conditional := expr_or_block else_clause
//! simple_pattern_match := pattern "then" conditional
//! else_clause := ε | "else" expr_or_block
//! guard_block := "{" (guard_arm, ",")* "}"
//! guard_arm := guard "->" expr_or_block
//! guard := "is" pattern | (operator)+ precedence_expr
//! ```
//!
//! ### While expressions
//! ```
//! while_expr := "while" while_cond "{" (statement delimiter)* "}"
//! while_cond := ε | expression | expression "is"  pattern //TODO maybe is-expresions should be primary
//! ```
//!
//! //TODO this implies there must be at least one enumerator, which the parser doesn"t support right
//! //this second, and maybe should fail later anyway
//! ### For-expressions
//! ```
//! for_expr := "for" (enumerator | "{" enumerators "}") for_expr_body
//! for_expr_body := "return" expression |  "{" (statement delimiter)* "}"
//! enumerators := enumerator ("," enumerators)*
//! enumerator :=  identifier "<-" expression | identifier "=" expression //TODO add guards, etc.
//! ```
//! 

use std::rc::Rc;
use std::iter::Peekable;
use std::vec::IntoIter;

use crate::tokenizing::*;
use crate::tokenizing::Kw::*;
use crate::tokenizing::TokenKind::*;

use crate::ast::*;

use crate::builtin::{BinOp, PrefixOp};

/// Represents a parsing error
#[derive(Debug)]
pub struct ParseError {
  pub msg: String,
  pub token: Token
}

impl ParseError {
  fn new_with_token<T, M>(msg: M, token: Token) -> ParseResult<T> where M: Into<String> {
    Err(ParseError { msg: msg.into(), token })
  }
}

/// Represents either a successful parsing result or a ParseError
pub type ParseResult<T> = Result<T, ParseError>;

#[derive(Debug)]
pub struct ParseRecord {
  production_name: String,
  next_token: String,
  level: u32,
}

/// Main data structure for doing parsing.
pub struct Parser {
  token_handler: TokenHandler,
  parse_record: Vec<ParseRecord>,
  parse_level: u32,
  restrictions: ParserRestrictions,
}

struct ParserRestrictions {
  no_struct_literal: bool
}

struct TokenHandler {
  tokens: Peekable<IntoIter<Token>>,
  end_of_file: (usize, usize),
}

impl TokenHandler {
  fn new(tokens: Vec<Token>) -> TokenHandler {
    let end_of_file = match tokens.last() {
      None => (0, 0),
      Some(t) => (t.line_num, t.char_num)
    };
    let tokens = tokens.into_iter().peekable();
    TokenHandler { tokens, end_of_file }
  }

  fn peek_kind(&mut self) -> TokenKind {
    self.tokens.peek().map(|ref t| { t.kind.clone() }).unwrap_or(TokenKind::EOF)
  }
  fn peek(&mut self) -> Token {
    self.tokens.peek().map(|t: &Token| { t.clone()}).unwrap_or(Token { kind: TokenKind::EOF, line_num: self.end_of_file.0, char_num: self.end_of_file.1})
  }
  fn next(&mut self) -> Token {
    self.tokens.next().unwrap_or(Token { kind: TokenKind::EOF, line_num: self.end_of_file.0, char_num: self.end_of_file.1})
  }
}

impl Parser {
  /// Create a new parser initialized with some tokens.
  pub fn new(initial_input: Vec<Token>) -> Parser {
    Parser {
      token_handler: TokenHandler::new(initial_input),
      parse_record: vec![],
      parse_level: 0,
      restrictions: ParserRestrictions { no_struct_literal: false }
    }
  }

  /// Parse all loaded tokens up to this point.
  pub fn parse(&mut self) -> ParseResult<AST> {
    self.program()
  }

  /*
  pub fn parse_with_new_tokens(&mut self, new_tokens: Vec<Token>) -> ParseResult<AST> {

  }
  */

  pub fn format_parse_trace(self) -> Vec<String> {
    self.parse_record.into_iter().map(|r| {
      let mut indent = String::new();
      for _ in 0..r.level {
        indent.push(' ');
      }
      format!("{}Production `{}`, token: {}", indent, r.production_name, r.next_token)
    }).collect()
  }
}

macro_rules! print_token_pattern {
  ($tokenpattern:pat) => { stringify!($tokenpattern) }
}

macro_rules! expect {
  ($self:expr, $token_kind:pat) => { expect!($self, $token_kind if true) };
  ($self:expr, $expected_kind:pat if $cond:expr) => {
    {
      let tok = $self.token_handler.peek();
      match tok.get_kind() {
        $expected_kind if $cond => $self.token_handler.next(),
        actual_kind => {
          let msg = format!("Expected {}, got {:?}", print_token_pattern!($expected_kind), actual_kind);
          return ParseError::new_with_token(msg, tok);
        }
      }
    }
  }
}

macro_rules! delimited {
  ($self:expr, $start:pat, $parse_fn:ident, $( $delim:pat )|+, $end:pat, nonstrict) => {
    delimited!($self, $start, $parse_fn, $( $delim )|*, $end, false)
  };
  ($self:expr, $start:pat, $parse_fn:ident, $( $delim:pat )|+, $end:pat) => {
    delimited!($self, $start, $parse_fn, $( $delim )|*, $end, true)
  };
  ($self:expr, $start:pat, $parse_fn:ident, $( $delim:pat )|+, $end:pat, $strictness:expr) => {
    {
      expect!($self, $start);
      let mut acc = vec![];
      loop {
        let peek = $self.token_handler.peek();
        match peek.get_kind() {
          $end | EOF => break,
          _ => (),
        }
        if !$strictness {
          match peek.get_kind() {
            $( $delim )|* => { $self.token_handler.next(); continue },
            _ => ()
          }
        }
        acc.push($self.$parse_fn()?);
        match $self.token_handler.peek().get_kind() {
          $( $delim )|* => { $self.token_handler.next(); continue },
          _ if $strictness => break,
          _ => continue,
        };
      }
      expect!($self, $end);
      acc
    }
  };
}


impl Parser {
  /// `program := (statement delimiter)* EOF`
  /// `delimiter := NEWLINE | ';'`
  #[recursive_descent_method]
  fn program(&mut self) -> ParseResult<AST> {
    let mut statements = Vec::new();
    loop {
      match self.token_handler.peek().get_kind() {
        EOF => break,
        Newline | Semicolon => {
          self.token_handler.next();
          continue;
        },
        _ => statements.push(
          Meta::new(self.statement()?)
        ),
      }
    }
    Ok(AST(statements))
  }

  /// `statement := expression | declaration`
  #[recursive_descent_method]
  fn statement(&mut self) -> ParseResult<Statement> {
    //TODO handle error recovery here
    match self.token_handler.peek().get_kind() {
      Keyword(Type) => self.type_declaration().map(|decl| { Statement::Declaration(decl) }),
      Keyword(Func)=> self.func_declaration().map(|func| { Statement::Declaration(func) }),
      Keyword(Let) => self.binding_declaration().map(|decl| Statement::Declaration(decl)),
      Keyword(Interface) => self.interface_declaration().map(|decl| Statement::Declaration(decl)),
      Keyword(Impl) => self.impl_declaration().map(|decl| Statement::Declaration(decl)),
      _ => self.expression().map(|expr| { Statement::ExpressionStatement(expr.into()) } ),
    }
  }

  #[recursive_descent_method]
  fn type_declaration(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Type));
    self.type_declaration_body()
  }

  #[recursive_descent_method]
  fn type_declaration_body(&mut self) -> ParseResult<Declaration> {
    if let Keyword(Alias) = self.token_handler.peek_kind() {
      self.type_alias()
    } else {
      let mutable = if let Keyword(Mut) = self.token_handler.peek_kind() {
        self.token_handler.next();
        true
      } else {
        false
      };
      let name = self.type_singleton_name()?;
      expect!(self, Operator(ref c) if **c == "=");
      let body = self.type_body()?;
      Ok(Declaration::TypeDecl { name, body, mutable})
    }
  }

  #[recursive_descent_method]
  fn type_alias(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Alias));
    let alias = self.identifier()?;
    expect!(self, Operator(ref c) if **c == "=");
    let original = self.identifier()?;
    Ok(Declaration::TypeAlias(alias, original))
  }

  #[recursive_descent_method]
  fn type_body(&mut self) -> ParseResult<TypeBody> {
    let mut variants = Vec::new();
    variants.push(self.variant_specifier()?);
    loop {
      if let Pipe = self.token_handler.peek_kind() {
        self.token_handler.next();
        variants.push(self.variant_specifier()?);
      } else {
        break;
      }
    }
    Ok(TypeBody(variants))
  }

  #[recursive_descent_method]
  fn variant_specifier(&mut self) -> ParseResult<Variant> {
    use self::Variant::*;

    let name = self.identifier()?;
    match self.token_handler.peek_kind() {
      LParen => {
        let tuple_members = delimited!(self, LParen, type_name, Comma, RParen);
        Ok(TupleStruct(name, tuple_members))
      },
      LCurlyBrace => {
        let typed_identifier_list = delimited!(self, LCurlyBrace, typed_identifier, Comma, RCurlyBrace);
        Ok(Record {name, members: typed_identifier_list })
      },
      _ => Ok(UnitStruct(name))
    }
  }

  #[recursive_descent_method]
  fn typed_identifier(&mut self) -> ParseResult<(Rc<String>, TypeIdentifier)> {
    let identifier = self.identifier()?;
    expect!(self, Colon);
    let type_name = self.type_name()?;
    Ok((identifier, type_name))
  }

  #[recursive_descent_method]
  fn func_declaration(&mut self) -> ParseResult<Declaration> {
    let signature = self.func_signature()?;
    if let LCurlyBrace = self.token_handler.peek_kind() {
      let statements = self.nonempty_func_body()?;
      Ok(Declaration::FuncDecl(signature, statements))
    } else {
      Ok(Declaration::FuncSig(signature))
    }
  }

  #[recursive_descent_method]
  fn func_signature(&mut self) -> ParseResult<Signature> {
    expect!(self, Keyword(Func));
    let (name, operator) = match self.token_handler.peek_kind() {
      Operator(s) => {
        let name = s.clone();
        self.token_handler.next();
        (name, true)
      },
      _ => (self.identifier()?, false)
    };
    let params = self.formal_param_list()?;
    let type_anno = match self.token_handler.peek_kind() {
      Colon => Some(self.type_anno()?),
      _ => None,
    };
    Ok(Signature { name, operator, params, type_anno })
  }

  #[recursive_descent_method]
  fn nonempty_func_body(&mut self) -> ParseResult<Vec<Meta<Statement>>> {
    let statements = delimited!(self, LCurlyBrace, statement, Newline | Semicolon, RCurlyBrace, nonstrict);
    Ok(statements.into_iter().map(|s| Meta::new(s)).collect())
  }

  #[recursive_descent_method]
  fn formal_param_list(&mut self) -> ParseResult<Vec<FormalParam>> {
    Ok(delimited!(self, LParen, formal_param, Comma, RParen))
  }

  #[recursive_descent_method]
  fn formal_param(&mut self) -> ParseResult<FormalParam> {
    let name = self.identifier()?;
    let ty = match self.token_handler.peek_kind() {
      Colon => Some(self.type_anno()?),
      _ => None
    };
    Ok((name, ty))
  }

  #[recursive_descent_method]
  fn binding_declaration(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Kw::Let));
    let constant = match self.token_handler.peek_kind() {
      Keyword(Kw::Mut) => {
        self.token_handler.next();
        false 
      }
      _ => true
    };
    let name = self.identifier()?;
    let type_anno = if let Colon = self.token_handler.peek_kind() {
      Some(self.type_anno()?)
    } else {
      None
    };

    expect!(self, Operator(ref o) if **o == "=");
    let expr = self.expression()?.into();

    Ok(Declaration::Binding { name, constant, type_anno, expr })
  }

  #[recursive_descent_method]
  fn interface_declaration(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Interface));
    let name = self.identifier()?;
    let signatures = self.signature_block()?;
    Ok(Declaration::Interface { name, signatures })
  }

  #[recursive_descent_method]
  fn signature_block(&mut self) -> ParseResult<Vec<Signature>> {
    Ok(delimited!(self, LCurlyBrace, func_signature, Newline | Semicolon, RCurlyBrace, nonstrict))
  }

  #[recursive_descent_method]
  fn impl_declaration(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Impl));
    let first = self.type_singleton_name()?;
    let second = if let Keyword(For) = self.token_handler.peek_kind() {
      self.token_handler.next();
      Some(self.type_name()?)
    } else {
      None
    };

    let block = self.decl_block()?;
    Ok(match (first, second) {
      (interface_name, Some(type_name)) =>
        Declaration::Impl { type_name, interface_name: Some(interface_name), block },
      (type_singleton_name, None) =>
        Declaration::Impl { type_name: TypeIdentifier::Singleton(type_singleton_name), interface_name: None, block }
    })
  }

  #[recursive_descent_method]
  fn decl_block(&mut self) -> ParseResult<Vec<Declaration>> {
    Ok(delimited!(self, LCurlyBrace, func_declaration, Newline | Semicolon, RCurlyBrace, nonstrict))
  }

  #[recursive_descent_method]
  fn expression(&mut self) -> ParseResult<Expression> {
    let mut expr_body = self.precedence_expr(BinOp::min_precedence())?;
    let type_anno = match self.token_handler.peek_kind() {
      Colon => Some(self.type_anno()?),
      _ => None
    };
    if let Some(_) = expr_body.1 {
      return ParseError::new_with_token("Bad parse state encountered", self.token_handler.peek());
    }
    expr_body.1 = type_anno;
    Ok(expr_body)
  }

  #[recursive_descent_method]
  fn type_anno(&mut self) -> ParseResult<TypeIdentifier> {
    expect!(self, Colon);
    self.type_name()
  }

  #[recursive_descent_method]
  fn type_name(&mut self) -> ParseResult<TypeIdentifier> {
    use self::TypeIdentifier::*;
    Ok(match self.token_handler.peek_kind() {
      LParen => Tuple(delimited!(self, LParen, type_name, Comma, RParen)),
      _ => Singleton(self.type_singleton_name()?),
    })
  }

  #[recursive_descent_method]
  fn type_singleton_name(&mut self) -> ParseResult<TypeSingletonName> {
    Ok(TypeSingletonName {
      name: self.identifier()?,
      params: match self.token_handler.peek_kind() {
        LAngleBracket => delimited!(self, LAngleBracket, type_name, Comma, RAngleBracket),
        _ => vec![],
      }
    })
  }

  // this implements Pratt parsing, see http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/
  fn precedence_expr(&mut self, precedence: i32) -> ParseResult<Expression> {
    let record = ParseRecord {
      production_name: "precedence_expr".to_string(),
      next_token: format!("{}", self.token_handler.peek().to_string_with_metadata()),
      level: self.parse_level,
    };
    self.parse_level += 1;
    self.parse_record.push(record);

    let mut lhs = self.prefix_expr()?;
    loop {
      let new_precedence = match BinOp::get_precedence_from_token(&self.token_handler.peek_kind()) {
        Some(p) => p,
        None => break,
      };

      if precedence >= new_precedence {
        break;
      }
      let next_tok = self.token_handler.next();
      let operation = match BinOp::from_sigil_token(&next_tok.kind) {
        Some(sigil) => sigil,
        None => unreachable!()
      };
      let rhs = self.precedence_expr(new_precedence)?;
      lhs = Expression(ExpressionKind::BinExp(operation, bx!(lhs.into()), bx!(rhs.into())), None);
    }
    self.parse_level -= 1;
    Ok(lhs)
  }

  #[recursive_descent_method]
  fn prefix_expr(&mut self) -> ParseResult<Expression> {
    match self.token_handler.peek_kind() {
      Operator(ref op) if PrefixOp::is_prefix(&*op) => {
        let sigil = match self.token_handler.next().kind {
          Operator(op) => op,
          _ => unreachable!(),
        };
        let expr = self.primary()?;
        Ok(Expression(
          ExpressionKind::PrefixExp(PrefixOp::from_sigil(sigil.as_str()), bx!(expr.into())),
          None
        ))
      },
      _ => self.call_expr()
    }
  }

  #[recursive_descent_method]
  fn call_expr(&mut self) -> ParseResult<Expression> {
    let mut expr = self.index_expr()?;
    while let LParen = self.token_handler.peek_kind() {
      let arguments = delimited!(self, LParen, invocation_argument, Comma, RParen);
      let arguments = arguments.into_iter().map(|s| Meta::new(s)).collect();
      expr = Expression(ExpressionKind::Call { f: bx!(expr.into()), arguments }, None); //TODO none is incorrect
    }

    Ok(expr)
  }

  #[recursive_descent_method]
  fn invocation_argument(&mut self) -> ParseResult<InvocationArgument> {
    Ok(match self.token_handler.peek_kind() {
      Underscore => {
        self.token_handler.next();
        InvocationArgument::Ignored
      },
      Identifier(s) => {
        self.token_handler.next();
        match self.token_handler.peek_kind() {
          Operator(ref op) if **op == "=" => {
            self.token_handler.next();
            let expr = self.expression()?;
            InvocationArgument::Keyword { name: s.clone(), expr }
          },
          _ => {
            let expr = self.expression()?;
            InvocationArgument::Positional(expr)
          }
        }
      },
      _ => InvocationArgument::Positional(self.expression()?)
    })
  }

  #[recursive_descent_method]
  fn index_expr(&mut self) -> ParseResult<Expression> {
    let primary = self.primary()?;
    Ok(if let LSquareBracket = self.token_handler.peek_kind() {
      let indexers = delimited!(self, LSquareBracket, expression, Comma, RSquareBracket)
        .into_iter().map(|ex| ex.into()).collect();
      Expression(ExpressionKind::Index {
        indexee: bx!(Expression(primary.0, None).into()),
        indexers,
      }, None)
    } else {
      primary
    })
  }

  #[recursive_descent_method]
  fn primary(&mut self) -> ParseResult<Expression> {
    match self.token_handler.peek_kind() {
      LCurlyBrace => self.curly_brace_expr(),
      Backslash => self.lambda_expr(),
      LParen => self.paren_expr(),
      LSquareBracket => self.list_expr(),
      Keyword(Kw::If) => self.if_expr(),
      Keyword(Kw::For) => self.for_expr(),
      Keyword(Kw::While) => self.while_expr(),
      Identifier(_) => self.identifier_expr(),
      _ => self.literal(),
    }
  }

  #[recursive_descent_method]
  fn list_expr(&mut self) -> ParseResult<Expression> {
    let exprs = delimited!(self, LSquareBracket, expression, Comma, RSquareBracket)
      .into_iter().map(|ex| ex.into()).collect();
    Ok(Expression(ExpressionKind::ListLiteral(exprs), None))
  }

  #[recursive_descent_method]
  fn curly_brace_expr(&mut self) -> ParseResult<Expression> {
    ParseError::new_with_token("Not implemented", self.token_handler.peek())
  }

  #[recursive_descent_method]
  fn lambda_expr(&mut self) -> ParseResult<Expression> {
    expect!(self, Backslash);
    let params = self.lambda_param_list()?;
    let type_anno = match self.token_handler.peek_kind() {
      Colon => Some(self.type_anno()?),
      _ => None,
    };
    let body = self.nonempty_func_body()?;
    Ok(Expression(ExpressionKind::Lambda { params, type_anno, body }, None)) //TODO need to handle types somehow
  }

  #[recursive_descent_method]
  fn lambda_param_list(&mut self) -> ParseResult<Vec<FormalParam>> {
    if let LParen = self.token_handler.peek_kind() {
      self.formal_param_list()
    } else {
      let single_param = self.formal_param()?;
      Ok(vec![single_param])
    }
  }

  #[recursive_descent_method]
  fn paren_expr(&mut self) -> ParseResult<Expression> {
    use self::ExpressionKind::*;
    let old_struct_value = self.restrictions.no_struct_literal;
    self.restrictions.no_struct_literal = false;
    let output = {
      let mut inner = delimited!(self, LParen, expression, Comma, RParen);
      match inner.len() {
        0 => Ok(Expression(TupleLiteral(vec![]), None)),
        1 => Ok(inner.pop().unwrap()),
        _ => {
          let inner: Vec<Meta<Expression>> = inner.into_iter().map(|ex| ex.into()).collect();
          Ok(Expression(TupleLiteral(inner), None))
        }
      }
    };
    self.restrictions.no_struct_literal = old_struct_value;
    output
  }

  #[recursive_descent_method]
  fn identifier_expr(&mut self) -> ParseResult<Expression> {
    use self::ExpressionKind::*;
    let identifier = self.identifier()?;
    Ok(match self.token_handler.peek_kind() {
      LCurlyBrace if !self.restrictions.no_struct_literal => {
        let fields = self.record_block()?;
        Expression(NamedStruct { name: identifier, fields }, None)
      },
      _ => Expression(Value(identifier), None)
    })
  }

  #[recursive_descent_method]
  fn record_block(&mut self) -> ParseResult<Vec<(Rc<String>, Meta<Expression>)>> {
    Ok(
      delimited!(self, LCurlyBrace, record_entry, Comma, RCurlyBrace)
      .into_iter().map(|(s, ex)| (s, ex.into())).collect()
    )
  }

  #[recursive_descent_method]
  fn record_entry(&mut self) -> ParseResult<(Rc<String>, Expression)> {
    let field_name = self.identifier()?;
    expect!(self, Colon);
    let value = self.expression()?;
    Ok((field_name, value))
  }

  #[recursive_descent_method]
  fn if_expr(&mut self) -> ParseResult<Expression> {
    expect!(self, Keyword(Kw::If));
    let discriminator = Box::new({
      self.restrictions.no_struct_literal = true;
      let x = self.discriminator();
      self.restrictions.no_struct_literal = false;
      x?
    });

    let body = Box::new(match self.token_handler.peek_kind() {
      Keyword(Kw::Then) => self.conditional()?,
      Keyword(Kw::Is) => self.simple_pattern_match()? ,
      _ => self.guard_block()?
    });

    Ok(Expression(ExpressionKind::IfExpression { discriminator, body }, None))
  }

  #[recursive_descent_method]
  fn discriminator(&mut self) -> ParseResult<Discriminator> {
    let lhs = self.prefix_expr()?;
    let ref next = self.token_handler.peek_kind();
    Ok(if let Some(op) = BinOp::from_sigil_token(next) {
      Discriminator::BinOp(lhs, op)
    } else {
      Discriminator::Simple(lhs)
    })
  }

  #[recursive_descent_method]
  fn conditional(&mut self) -> ParseResult<IfExpressionBody> {
    expect!(self, Keyword(Kw::Then));
    let then_clause = self.expr_or_block()?;
    let else_clause = self.else_clause()?;
    Ok(IfExpressionBody::SimpleConditional(then_clause, else_clause))
  }

  #[recursive_descent_method]
  fn simple_pattern_match(&mut self) -> ParseResult<IfExpressionBody> {
    expect!(self, Keyword(Kw::Is));
    let pat = self.pattern()?;
    expect!(self, Keyword(Kw::Then));
    let then_clause = self.expr_or_block()?;
    let else_clause = self.else_clause()?;
    Ok(IfExpressionBody::SimplePatternMatch(pat, then_clause, else_clause))
  }

  #[recursive_descent_method]
  fn else_clause(&mut self) -> ParseResult<Option<Block>> {
    Ok(if let Keyword(Kw::Else) = self.token_handler.peek_kind() {
      self.token_handler.next();
      Some(self.expr_or_block()?)
    } else {
      None
    })
  }

  #[recursive_descent_method]
  fn guard_block(&mut self) -> ParseResult<IfExpressionBody> {
    //TODO - delimited! isn't sophisticated enough to do thisa
    //let guards = delimited!(self, LCurlyBrace, guard_arm, Comma, RCurlyBrace);
    expect!(self, LCurlyBrace);

    let mut guards = vec![];
    loop {
      match self.token_handler.peek_kind() {
        RCurlyBrace | EOF => break,
        Semicolon | Newline => { self.token_handler.next(); continue},
        _ => {
          let guard_arm = self.guard_arm()?;
          guards.push(guard_arm);
          loop {
            match self.token_handler.peek_kind() {
              Semicolon | Newline => { self.token_handler.next(); continue; },
              _ => break,
            }
          }
          if let RCurlyBrace = self.token_handler.peek_kind() {
            break;
          }
          expect!(self, Comma);
        }
      }
    }
    expect!(self, RCurlyBrace);
    Ok(IfExpressionBody::GuardList(guards))
  }

  #[recursive_descent_method]
  fn guard_arm(&mut self) -> ParseResult<GuardArm> {
    let guard = self.guard()?;
    expect!(self, Operator(ref c) if **c == "->");
    let body = self.expr_or_block()?;
    Ok(GuardArm { guard, body })
  }

  #[recursive_descent_method]
  fn guard(&mut self) -> ParseResult<Guard> {
    Ok(match self.token_handler.peek_kind() {
      Keyword(Kw::Is) => {
        self.token_handler.next();
        let pat = self.pattern()?;
        Guard::Pat(pat)
      },
      ref tok if BinOp::from_sigil_token(tok).is_some() => {
        let op = BinOp::from_sigil_token(&self.token_handler.next().kind).unwrap();
        let precedence = op.get_precedence();
        let Expression(expr, _) = self.precedence_expr(precedence)?;
        Guard::HalfExpr(HalfExpr { op: Some(op), expr })
      },
      _ => {
        //TODO - I think there's a better way to do this involving the precedence of ->
        let Expression(expr, _) = self.prefix_expr()?;
        Guard::HalfExpr(HalfExpr { op: None, expr })
      }
    })
  }

  #[recursive_descent_method]
  fn pattern(&mut self) -> ParseResult<Pattern> {
    if let LParen = self.token_handler.peek_kind() {
      let tuple_pattern_variants = delimited!(self, LParen, pattern, Comma, RParen);
      Ok(Pattern::TuplePattern(tuple_pattern_variants))
    } else {
      self.simple_pattern()
    }
  }

  #[recursive_descent_method]
  fn simple_pattern(&mut self) -> ParseResult<Pattern> {
    Ok({
      let tok = self.token_handler.peek();
      match tok.get_kind() {
        Identifier(_) => {
          let id = self.identifier()?;
          match self.token_handler.peek_kind() {
            LCurlyBrace => {
              let members = delimited!(self, LCurlyBrace, record_pattern_entry, Comma, RCurlyBrace);
              Pattern::Record(id, members)
            },
            LParen => {
              let members = delimited!(self, LParen, pattern, Comma, RParen);
              Pattern::TupleStruct(id, members)
            },
            _ => Pattern::Literal(PatternLiteral::VarPattern(id))
          }
        },
        Keyword(Kw::True) => {
          self.token_handler.next();
          Pattern::Literal(PatternLiteral::BoolPattern(true))
        },
        Keyword(Kw::False) => {
          self.token_handler.next();
          Pattern::Literal(PatternLiteral::BoolPattern(false))
        },
        StrLiteral(s) => {
          self.token_handler.next();
          Pattern::Literal(PatternLiteral::StringPattern(s))
        },
        DigitGroup(_) | HexLiteral(_) | BinNumberSigil | Period => self.signed_number_literal()?,
        Operator(ref op) if **op == "-" => self.signed_number_literal()?,
        Underscore => {
          self.token_handler.next();
          Pattern::Ignored
        },
        other => return ParseError::new_with_token(format!("{:?} is not a valid Pattern", other), tok)
      }
    })
  }

  #[recursive_descent_method]
  fn signed_number_literal(&mut self) -> ParseResult<Pattern> {
    let neg = match self.token_handler.peek_kind() {
      Operator(ref op) if **op == "-" => {
        self.token_handler.next();
        true
      },
      _ => false
    };
    let Expression(expr_type, _) = self.number_literal()?;
    Ok(Pattern::Literal(PatternLiteral::NumPattern { neg, num: expr_type }))
  }

  #[recursive_descent_method]
  fn record_pattern_entry(&mut self) -> ParseResult<(Rc<String>, Pattern)> {
    let name = self.identifier()?;
    Ok(match self.token_handler.peek_kind() {
      Colon => {
        expect!(self, Colon);
        let pat = self.pattern()?;
        (name, pat)
      },
      _ => (name.clone(), Pattern::Literal(PatternLiteral::StringPattern(name.clone())))
    })
  }

  #[recursive_descent_method]
  fn block(&mut self) -> ParseResult<Block> {
    let block = delimited!(self, LCurlyBrace, statement, Newline | Semicolon, RCurlyBrace, nonstrict);
    Ok(block.into_iter().map(|s| { Meta::new(s) }).collect())
  }

  #[recursive_descent_method]
  fn expr_or_block(&mut self) -> ParseResult<Block> {
    match self.token_handler.peek_kind() {
      LCurlyBrace => self.block(),
      _ => {
        let expr = self.expression()?;
        Ok(vec![Meta::new(Statement::ExpressionStatement(expr.into()))])
      }
    }
  }

  #[recursive_descent_method]
  fn while_expr(&mut self) -> ParseResult<Expression> {
    use self::ExpressionKind::*;
    expect!(self, Keyword(Kw::While));
    let condition =  {
      self.restrictions.no_struct_literal = true;
      let x = self.while_cond();
      self.restrictions.no_struct_literal = false;
      x?.map(|expr| bx!(expr.into()))
    };
    let body = self.block()?;
    Ok(Expression(WhileExpression {condition, body}, None))
  }

  #[recursive_descent_method]
  fn while_cond(&mut self) -> ParseResult<Option<Expression>> {
    Ok(match self.token_handler.peek_kind() {
      LCurlyBrace => None,
      _ => Some(self.expression()?),
    })
  }

  #[recursive_descent_method]
  fn for_expr(&mut self) -> ParseResult<Expression> {
    expect!(self, Keyword(Kw::For));
    let enumerators = if let LCurlyBrace = self.token_handler.peek_kind() {
      delimited!(self, LCurlyBrace, enumerator, Comma | Newline, RCurlyBrace)
    } else {
      let single_enum = {
        self.restrictions.no_struct_literal = true;
        let s = self.enumerator();
        self.restrictions.no_struct_literal = false;
        s?
      };
      vec![single_enum]
    };
    let body = Box::new(self.for_expr_body()?);
    Ok(Expression(ExpressionKind::ForExpression { enumerators, body }, None))
  }

  #[recursive_descent_method]
  fn enumerator(&mut self) -> ParseResult<Enumerator> {
    let id = self.identifier()?;
    expect!(self, Operator(ref c) if **c == "<-");
    let generator = self.expression()?.into();
    Ok(Enumerator { id, generator })
  }

  #[recursive_descent_method]
  fn for_expr_body(&mut self) -> ParseResult<ForBody> {
    use self::ForBody::*;
    let tok = self.token_handler.peek();
    Ok(match tok.get_kind() {
      LCurlyBrace => {
        let statements = delimited!(self, LCurlyBrace, statement, Newline | Semicolon, RCurlyBrace, nonstrict);
        StatementBlock(statements.into_iter().map(|s| Meta::new(s)).collect())
      },
      Keyword(Kw::Return) => {
        self.token_handler.next();
        MonadicReturn(self.expression()?.into())
      },
      _ => return ParseError::new_with_token("for expressions must end in a block or 'return'", tok),
    })
  }

  #[recursive_descent_method]
  fn identifier(&mut self) -> ParseResult<Rc<String>> {
    let tok = self.token_handler.next();
    match tok.get_kind() {
      Identifier(s) => Ok(s),
      p => ParseError::new_with_token(format!("Expected an identifier, got {:?}", p), tok),
    }
  }

  #[recursive_descent_method]
  fn literal(&mut self) -> ParseResult<Expression> {
    use self::ExpressionKind::*;

    let tok = self.token_handler.peek();
    match tok.get_kind() {
      DigitGroup(_) | HexLiteral(_) | BinNumberSigil | Period => self.number_literal(),
      Keyword(Kw::True) => {
        self.token_handler.next();
        Ok(Expression(BoolLiteral(true), None))
      },
      Keyword(Kw::False) => {
        self.token_handler.next();
        Ok(Expression(BoolLiteral(false), None))
      },
      StrLiteral(s) => {
        self.token_handler.next();
        Ok(Expression(StringLiteral(s.clone()), None))
      }
      e => ParseError::new_with_token(format!("Expected a literal expression, got {:?}", e), tok),
    }
  }

  #[recursive_descent_method]
  fn number_literal(&mut self) -> ParseResult<Expression> {
    match self.token_handler.peek_kind() {
      HexLiteral(_) | BinNumberSigil => self.int_literal(),
      _ => self.float_literal(),
    }
  }

  #[recursive_descent_method]
  fn int_literal(&mut self) -> ParseResult<Expression> {
    use self::ExpressionKind::*;
    let tok = self.token_handler.next();
    match tok.get_kind() {
      BinNumberSigil => {
        let digits = self.digits()?;
        let n = parse_binary(digits, tok)?;
        Ok(Expression(NatLiteral(n), None))
      },
      HexLiteral(text) => {
        let digits: String = text.chars().filter(|c| c.is_digit(16)).collect();
        let n = parse_hex(digits, tok)?;
        Ok(Expression(NatLiteral(n), None))
      },
      _ => return ParseError::new_with_token("Expected '0x' or '0b'", tok),
    }
  }

  #[recursive_descent_method]
  fn float_literal(&mut self) -> ParseResult<Expression> {
    use self::ExpressionKind::*;
    let tok = self.token_handler.peek();
    let mut digits = self.digits()?;
    if let Period = self.token_handler.peek_kind() {
      self.token_handler.next();
      digits.push_str(".");
      digits.push_str(&self.digits()?);
      match digits.parse::<f64>() {
        Ok(f) => Ok(Expression(FloatLiteral(f), None)),
        Err(e) => ParseError::new_with_token(format!("Float failed to parse with error: {}", e), tok),

      }
    } else {
      match digits.parse::<u64>() {
        Ok(d) => Ok(Expression(NatLiteral(d), None)),
        Err(e) => ParseError::new_with_token(format!("Integer failed to parse with error: {}", e), tok),
      }
    }
  }

  #[recursive_descent_method]
  fn digits(&mut self) -> ParseResult<String> {
    let mut ds = String::new();
    loop {
      match self.token_handler.peek_kind() {
        Underscore => { self.token_handler.next(); continue; },
        DigitGroup(ref s) => { self.token_handler.next(); ds.push_str(s)},
        _ => break,
      }
    }
    Ok(ds)
  }
}

fn parse_binary(digits: String, tok: Token) -> ParseResult<u64> {
  let mut result: u64 = 0;
  let mut multiplier = 1;
  for d in digits.chars().rev() {
    match d {
      '1' => result += multiplier,
      '0' => (),
      _ => return ParseError::new_with_token("Encountered a character not '1' or '0 while parsing a binary literal", tok),
    }
    multiplier = match multiplier.checked_mul(2) {
      Some(m) => m,
      None => return ParseError::new_with_token("This binary expression will overflow", tok)
    }
  }
  Ok(result)
}

fn parse_hex(digits: String, tok: Token) -> ParseResult<u64> {
  let mut result: u64 = 0;
  let mut multiplier: u64 = 1;
  for d in digits.chars().rev() {
    match d.to_digit(16) {
      Some(n) => result += n as u64 * multiplier,
      None => return ParseError::new_with_token("Encountered a non-hex digit in a hex literal", tok),
    }
    multiplier = match multiplier.checked_mul(16) {
      Some(m) => m,
      None => return ParseError::new_with_token("This hex expression will overflow", tok)
    }
  }
  Ok(result)
}

#[cfg(test)]
mod parse_tests {
  use ::std::rc::Rc;
  use super::tokenize;
  use super::ParseResult;
  use crate::builtin::{PrefixOp, BinOp};
  use crate::ast::{AST, Meta, Expression, Statement, IfExpressionBody, Discriminator, Pattern, PatternLiteral, TypeBody, Enumerator, ForBody, InvocationArgument};
  use super::Statement::*;
  use super::Declaration::*;
  use super::Signature;
  use super::TypeIdentifier::*;
  use super::TypeSingletonName;
  use super::ExpressionKind::*;
  use super::Variant::*;
  use super::ForBody::*;

  fn parse(input: &str) -> ParseResult<AST> {
    let tokens: Vec<crate::tokenizing::Token> = tokenize(input);
    let mut parser = super::Parser::new(tokens);
    parser.parse()
  }

  macro_rules! parse_test {
    ($string:expr, $correct:expr) => { assert_eq!(parse($string).unwrap(), $correct) };
  }
  macro_rules! parse_test_wrap_ast {
    ($string:expr, $correct:expr) => { parse_test!($string, AST(vec![$correct])) }
  }
  macro_rules! parse_error {
    ($string:expr) => { assert!(parse($string).is_err()) }
  }
  macro_rules! val {
    ($var:expr) => { Value(Rc::new($var.to_string())) }
  }
  macro_rules! ty {
    ($name:expr) => { Singleton(tys!($name)) }
  }
  macro_rules! tys {
    ($name:expr) => { TypeSingletonName { name: Rc::new($name.to_string()), params: vec![] } };
  }

  macro_rules! ex {
    ($expr_type:expr) => { Expression($expr_type, None) };
    (m $expr_type:expr) => { Meta::new(Expression($expr_type, None)) };
    (m $expr_type:expr, $type_anno:expr) => { Meta::new(Expression($expr_type, Some($type_anno))) };
    (s $expr_text:expr) => {
      {
        let tokens: Vec<crate::tokenizing::Token> = tokenize($expr_text);
        let mut parser = super::Parser::new(tokens);
        parser.expression().unwrap()
      }
    };
  }

  macro_rules! inv {
    ($expr_type:expr) => { Meta::new(InvocationArgument::Positional(ex!($expr_type))) }
  }

  macro_rules! binexp {
    ($op:expr, $lhs:expr, $rhs:expr) => { BinExp(BinOp::from_sigil($op), bx!(Expression($lhs, None).into()), bx!(Expression($rhs, None).into())) }
  }
  macro_rules! prefexp {
    ($op:expr, $lhs:expr) => { PrefixExp(PrefixOp::from_sigil($op), bx!(Expression($lhs, None).into())) }
  }
  macro_rules! exst {
    ($expr_type:expr) => { Meta::new(Statement::ExpressionStatement(Expression($expr_type, None).into())) };
    ($expr_type:expr, $type_anno:expr) => { Meta::new(Statement::ExpressionStatement(Expression($expr_type, Some($type_anno)).into())) };
    ($op:expr, $lhs:expr, $rhs:expr) => { Meta::new(Statement::ExpressionStatement(ex!(binexp!($op, $lhs, $rhs)))) };
    (s $statement_text:expr) => {
      {
        let tokens: Vec<crate::tokenizing::Token> = tokenize($statement_text);
        let mut parser = super::Parser::new(tokens);
        Meta::new(parser.statement().unwrap())
      }
    }
  }

  #[test]
  fn parsing_number_literals_and_binexps() {
    parse_test_wrap_ast! { ".2", exst!(FloatLiteral(0.2)) };
    parse_test_wrap_ast! { "8.1", exst!(FloatLiteral(8.1)) };

    parse_test_wrap_ast! { "0b010", exst!(NatLiteral(2)) };
    parse_test_wrap_ast! { "0b0_1_0_", exst!(NatLiteral(2)) }

    parse_test_wrap_ast! {"0xff", exst!(NatLiteral(255)) };
    parse_test_wrap_ast! {"0xf_f_", exst!(NatLiteral(255)) };

    parse_test_wrap_ast! {"0xf_f_+1", exst!(binexp!("+", NatLiteral(255), NatLiteral(1))) };

    parse_test! {"3; 4; 4.3", AST(
      vec![exst!(NatLiteral(3)), exst!(NatLiteral(4)),
        exst!(FloatLiteral(4.3))])
    };

    parse_test!("1 + 2 * 3", AST(vec!
      [
        exst!(binexp!("+", NatLiteral(1), binexp!("*", NatLiteral(2), NatLiteral(3))))
      ]));

    parse_test!("1 * 2 + 3", AST(vec!
      [
        exst!(binexp!("+", binexp!("*", NatLiteral(1), NatLiteral(2)), NatLiteral(3)))
      ]));

    parse_test!("1 && 2", AST(vec![exst!(binexp!("&&", NatLiteral(1), NatLiteral(2)))]));

    parse_test!("1 + 2 * 3 + 4", AST(vec![exst!(
      binexp!("+",
        binexp!("+", NatLiteral(1), binexp!("*", NatLiteral(2), NatLiteral(3))),
        NatLiteral(4)))]));

    parse_test!("(1 + 2) * 3", AST(vec!
      [exst!(binexp!("*", binexp!("+", NatLiteral(1), NatLiteral(2)), NatLiteral(3)))]));

    parse_test!(".1 + .2", AST(vec![exst!(binexp!("+", FloatLiteral(0.1), FloatLiteral(0.2)))]));
    parse_test!("1 / 2", AST(vec![exst!(binexp!("/", NatLiteral(1), NatLiteral(2)))]));
  }

  #[test]
  fn parsing_tuples() {
    parse_test!("()", AST(vec![exst!(TupleLiteral(vec![]))]));
    parse_test!("(\"hella\", 34)", AST(vec![exst!(
      TupleLiteral(
        vec![ex!(s r#""hella""#).into(), ex!(s "34").into()]
      )
    )]));
    parse_test!("((1+2), \"slough\")", AST(vec![exst!(TupleLiteral(vec![
      ex!(binexp!("+", NatLiteral(1), NatLiteral(2))).into(),
      ex!(StringLiteral(rc!(slough))).into(),
    ]))]))
  }

  #[test]
  fn parsing_identifiers() {
    parse_test!("a", AST(vec![exst!(val!("a"))]));
    parse_test!("some_value", AST(vec![exst!(val!("some_value"))]));
    parse_test!("a + b", AST(vec![exst!(binexp!("+", val!("a"), val!("b")))]));
    //parse_test!("a[b]", AST(vec![Expression(
    //parse_test!("a[]", <- TODO THIS NEEDS TO FAIL
    //parse_test("a()[b]()[d]")
    //TODO fix this parsing stuff
    /*
    parse_test! { "perspicacity()[a]", AST(vec![
      exst!(Index {
        indexee: bx!(ex!(Call { f: bx!(ex!(val!("perspicacity"))), arguments: vec![] })),
        indexers: vec![ex!(val!("a"))]
      })
    ]) 
    }
    */
    parse_test!("a[b,c]", AST(vec![exst!(Index { indexee: bx!(ex!(m val!("a"))), indexers: vec![ex!(m val!("b")), ex!(m val!("c"))]} )]));

    parse_test!("None", AST(vec![exst!(val!("None"))]));
    parse_test!("Pandas {  a: x + y }", AST(vec![
      exst!(NamedStruct { name: rc!(Pandas), fields: vec![(rc!(a), ex!(m binexp!("+", val!("x"), val!("y"))))]})
    ]));
    parse_test! { "Pandas { a: n, b: q, }",
    AST(vec![
        exst!(NamedStruct { name: rc!(Pandas), fields:
          vec![(rc!(a), ex!(m val!("n"))), (rc!(b), ex!(m val!("q")))]
          }
        )
      ])
    };
  }

  #[test]
  fn parsing_complicated_operators() {
    parse_test!("a <- b", AST(vec![exst!(binexp!("<-", val!("a"), val!("b")))]));
    parse_test!("a || b", AST(vec![exst!(binexp!("||", val!("a"), val!("b")))]));
    parse_test!("a<>b", AST(vec![exst!(binexp!("<>", val!("a"), val!("b")))]));
    parse_test!("a.b.c.d", AST(vec![exst!(binexp!(".",
                                                binexp!(".",
                                                  binexp!(".", val!("a"), val!("b")),
                                                val!("c")),
                                               val!("d")))]));
    parse_test!("-3", AST(vec![exst!(prefexp!("-", NatLiteral(3)))]));
    parse_test!("-0.2", AST(vec![exst!(prefexp!("-", FloatLiteral(0.2)))]));
    parse_test!("!3", AST(vec![exst!(prefexp!("!", NatLiteral(3)))]));
    parse_test!("a <- -b", AST(vec![exst!(binexp!("<-", val!("a"), prefexp!("-", val!("b"))))]));
    parse_test!("a <--b", AST(vec![exst!(binexp!("<--", val!("a"), val!("b")))]));
  }

  #[test]
  fn parsing_functions() {
    parse_test!("fn oi()",  AST(vec![Meta::new(Declaration(FuncSig(Signature { name: rc!(oi), operator: false, params: vec![], type_anno: None })))]));
    parse_test!("oi()", AST(vec![exst!(Call { f: bx!(ex!(m val!("oi"))), arguments: vec![] })]));
    parse_test!("oi(a, 2 + 2)", AST(vec![exst!(Call
    { f: bx!(ex!(m val!("oi"))),
      arguments: vec![inv!(val!("a")).into(), inv!(binexp!("+", NatLiteral(2), NatLiteral(2))).into()]
    })]));
    parse_error!("a(b,,c)");

    parse_test!("fn a(b, c: Int): Int", AST(vec![Meta::new(Declaration(
      FuncSig(Signature { name: rc!(a), operator: false, params: vec![
        (rc!(b), None), (rc!(c), Some(ty!("Int")))
      ], type_anno: Some(ty!("Int")) })))]));


    parse_test!("fn a(x) { x() }", AST(vec![Meta::new(Declaration(
      FuncDecl(Signature { name: rc!(a), operator: false, params: vec![(rc!(x),None)], type_anno: None },
        vec![exst!(Call { f: bx!(ex!(m val!("x"))), arguments: vec![] })])))]));
    parse_test!("fn a(x) {\n x() }", AST(vec![Meta::new(Declaration(
      FuncDecl(Signature { name: rc!(a), operator: false, params: vec![(rc!(x),None)], type_anno: None },
        vec![exst!(Call { f: bx!(ex!(m val!("x"))), arguments: vec![] })])))]));

    let multiline = r#"
fn a(x) {
  x()
}
"#;
    parse_test!(multiline, AST(vec![Meta::new(Declaration(
      FuncDecl(Signature { name: rc!(a), operator: false, params: vec![(rc!(x),None)], type_anno: None },
        vec![exst!(Call { f: bx!(ex!(m val!("x"))), arguments: vec![] })])))]));
    let multiline2 = r#"
fn a(x) {

  x()

}
"#;
    parse_test!(multiline2, AST(vec![Meta::new(Declaration(
      FuncDecl(Signature { name: rc!(a), operator: false, params: vec![(rc!(x),None)], type_anno: None },
        vec![exst!(s "x()")])))]));
  }

  #[test]
  fn parsing_bools() {
    parse_test!("false", AST(vec![exst!(BoolLiteral(false))]));
    parse_test!("true", AST(vec![exst!(BoolLiteral(true))]));
  }

  #[test]
  fn parsing_strings() {
    parse_test!(r#""hello""#, AST(vec![exst!(StringLiteral(rc!(hello)))]));
  }

  #[test]
  fn parsing_types() {
    parse_test!("type Yolo = Yolo", AST(vec![Meta::new(Declaration(TypeDecl { name: tys!("Yolo"), body: TypeBody(vec![UnitStruct(rc!(Yolo))]), mutable: false} ))]));
    parse_test!("type mut Yolo = Yolo", AST(vec![Meta::new(Declaration(TypeDecl { name: tys!("Yolo"), body: TypeBody(vec![UnitStruct(rc!(Yolo))]), mutable: true} ))]));
    parse_test!("type alias Sex = Drugs", AST(vec![Meta::new(Declaration(TypeAlias(rc!(Sex), rc!(Drugs))))]));
    parse_test!("type Sanchez = Miguel | Alejandro(Int, Option<a>) | Esperanza { a: Int, b: String }",
    AST(vec![Meta::new(Declaration(TypeDecl{
      name: tys!("Sanchez"),
      body: TypeBody(vec![
        UnitStruct(rc!(Miguel)),
        TupleStruct(rc!(Alejandro), vec![
          Singleton(TypeSingletonName { name: rc!(Int), params: vec![] }),
          Singleton(TypeSingletonName { name: rc!(Option), params: vec![Singleton(TypeSingletonName { name: rc!(a), params: vec![] })] }),
        ]),
        Record{
          name: rc!(Esperanza),
          members: vec![
            (rc!(a), Singleton(TypeSingletonName { name: rc!(Int), params: vec![] })),
            (rc!(b), Singleton(TypeSingletonName { name: rc!(String), params: vec![] })),
          ]
        }
      ]),
      mutable: false
    }))]));

    parse_test!("type Jorge<a> = Diego | Kike(a)", AST(vec![
      Meta::new(Declaration(TypeDecl{
        name: TypeSingletonName { name: rc!(Jorge), params: vec![Singleton(TypeSingletonName { name: rc!(a), params: vec![] })] },
        body: TypeBody(vec![UnitStruct(rc!(Diego)), TupleStruct(rc!(Kike), vec![Singleton(TypeSingletonName { name: rc!(a), params: vec![] })])]),
        mutable: false
      }
    ))]));
  }

  #[test]
  fn parsing_bindings() {
    parse_test!("let mut a = 10", AST(vec![Meta::new(Declaration(Binding { name: rc!(a), constant: false, type_anno: None, expr: ex!(m NatLiteral(10)) } ))]));
    parse_test!("let a = 2 + 2", AST(vec![Meta::new(Declaration(Binding { name: rc!(a), constant: true, type_anno: None, expr: ex!(m binexp!("+", NatLiteral(2), NatLiteral(2))) }) )]));
    parse_test!("let a: Nat = 2 + 2", AST(vec![Meta::new(Declaration(
      Binding { name: rc!(a), constant: true, type_anno: Some(Singleton(TypeSingletonName { name: rc!(Nat), params: vec![] })),
      expr: Meta::new(ex!(binexp!("+", NatLiteral(2), NatLiteral(2)))) }
    ))]));
  }

  #[test]
  fn parsing_block_expressions() {
    parse_test! {
      "if a() then { b(); c() }", AST(vec![exst!(
        IfExpression {
          discriminator: bx! {
            Discriminator::Simple(ex!(Call { f: bx!(ex!(m val!("a"))), arguments: vec![]}))
          },
          body: bx! {
            IfExpressionBody::SimpleConditional(
              vec![exst!(Call { f: bx!(ex!(m val!("b"))), arguments: vec![]}), exst!(Call { f: bx!(ex!(m val!("c"))), arguments: vec![] })],
              None
            )
          }
        }
      )])
    };

    parse_test! {
      "if a() then { b(); c() } else { q }", AST(vec![exst!(
        IfExpression {
          discriminator: bx! {
            Discriminator::Simple(ex!(Call { f: bx!(ex!(m val!("a"))), arguments: vec![]}))
          },
          body: bx! {
            IfExpressionBody::SimpleConditional(
              vec![exst!(Call { f: bx!(ex!(m val!("b"))), arguments: vec![]}), exst!(Call { f: bx!(ex!(m val!("c"))), arguments: vec![] })],
              Some(
                vec![exst!(val!("q"))],
              )
            )
          }
        }
      )])
    };

    /*
    parse_test!("if a() then { b(); c() }", AST(vec![exst!(
        IfExpression(bx!(ex!(Call { f: bx!(ex!(val!("a"))), arguments: vec![]})),
          vec![exst!(Call { f: bx!(ex!(val!("b"))), arguments: vec![]}), exst!(Call { f: bx!(ex!(val!("c"))), arguments: vec![] })],
          None)
        )]));
    parse_test!(r#"
    if true then {
      const a = 10
      b
    } else {
      c
    }"#,
    AST(vec![exst!(IfExpression(bx!(ex!(BoolLiteral(true))),
      vec![Declaration(Binding { name: rc!(a), constant: true, expr: ex!(NatLiteral(10)) }),
           exst!(val!(rc!(b)))],
      Some(vec![exst!(val!(rc!(c)))])))])
    );

    parse_test!("if a { b } else { c }", AST(vec![exst!(
          IfExpression(bx!(ex!(val!("a"))),
            vec![exst!(val!("b"))],
            Some(vec![exst!(val!("c"))])))]));

    parse_test!("if (A {a: 1}) { b } else { c }", AST(vec![exst!(
          IfExpression(bx!(ex!(NamedStruct { name: rc!(A), fields: vec![(rc!(a), ex!(NatLiteral(1)))]})),
            vec![exst!(val!("b"))],
            Some(vec![exst!(val!("c"))])))]));

    parse_error!("if A {a: 1} { b } else { c }");
    */
  }
  #[test]
  fn parsing_interfaces() {
    parse_test!("interface Unglueable { fn unglue(a: Glue); fn mar(): Glue }", AST(vec![
      Meta::new(Declaration(Interface {
        name: rc!(Unglueable),
        signatures: vec![
          Signature { name: rc!(unglue), operator: false, params: vec![(rc!(a), Some(Singleton(TypeSingletonName { name: rc!(Glue), params: vec![] })))], type_anno: None },
          Signature { name: rc!(mar), operator: false, params: vec![], type_anno: Some(Singleton(TypeSingletonName { name: rc!(Glue), params: vec![] })) },
        ]
      }))
    ]));
  }

  #[test]
  fn parsing_impls() {
    parse_test!("impl Heh { fn yolo(); fn swagg(); }", AST(vec![
      Meta::new(
      Declaration(Impl {
        type_name: ty!("Heh"),
        interface_name: None,
        block: vec![
          FuncSig(Signature { name: rc!(yolo), operator: false, params: vec![], type_anno: None }),
          FuncSig(Signature { name: rc!(swagg), operator: false, params: vec![], type_anno: None })
        ] }))]));

    parse_test!("impl Mondai for Lollerino { fn yolo(); fn swagg(); }", AST(vec![
      Meta::new(Declaration(Impl {
        type_name: ty!("Lollerino"),
        interface_name: Some(TypeSingletonName { name: rc!(Mondai), params: vec![] }),
        block: vec![
          FuncSig(Signature { name: rc!(yolo), operator: false, params: vec![], type_anno: None}),
          FuncSig(Signature { name: rc!(swagg), operator: false, params: vec![], type_anno: None })
        ] }))]));

    parse_test!("impl Hella<T> for (Alpha, Omega) { }", AST(vec![
      Meta::new(Declaration(Impl {
        type_name: Tuple(vec![ty!("Alpha"), ty!("Omega")]),
        interface_name: Some(TypeSingletonName { name: rc!(Hella), params: vec![ty!("T")] }),
        block: vec![]
      }))
    ]));

    parse_test!("impl Option<WTFMate> { fn oi() }", AST(vec![
      Meta::new(
      Declaration(Impl {
        type_name: Singleton(TypeSingletonName { name: rc!(Option), params: vec![ty!("WTFMate")]}),
        interface_name: None,
        block: vec![
          FuncSig(Signature { name: rc!(oi), operator: false, params: vec![], type_anno: None }),
        ]
      }))]));
  }

  #[test]
  fn parsing_type_annotations() {
    parse_test!("let a = b : Int", AST(vec![
      Meta::new(
      Declaration(Binding { name: rc!(a), constant: true, type_anno: None, expr:
        ex!(m val!("b"), ty!("Int")) }))]));

    parse_test!("a : Int", AST(vec![
      exst!(val!("a"), ty!("Int"))
    ]));

    parse_test!("a : Option<Int>", AST(vec![
      exst!(val!("a"), Singleton(TypeSingletonName { name: rc!(Option), params: vec![ty!("Int")] }))
    ]));

    parse_test!("a : KoreanBBQSpecifier<Kimchi, Option<Bulgogi> >", AST(vec![
      exst!(val!("a"), Singleton(TypeSingletonName { name: rc!(KoreanBBQSpecifier), params: vec![
        ty!("Kimchi"), Singleton(TypeSingletonName { name: rc!(Option), params: vec![ty!("Bulgogi")] })
      ] }))
    ]));

    parse_test!("a : (Int, Yolo<a>)", AST(vec![
      exst!(val!("a"), Tuple(
        vec![ty!("Int"), Singleton(TypeSingletonName {
          name: rc!(Yolo), params: vec![ty!("a")]
        })]))]));
  }

  #[test]
  fn parsing_lambdas() {
    parse_test_wrap_ast! { r#"\(x) { x + 1}"#, exst!(
        Lambda { params: vec![(rc!(x), None)], type_anno: None, body: vec![exst!(s "x + 1")] }
      ) 
    }

    parse_test!(r#"\  (x: Int, y) { a;b;c;}"#, AST(vec![
      exst!(Lambda {
        params: vec![(rc!(x), Some(ty!("Int"))), (rc!(y), None)],
        type_anno: None,
        body: vec![exst!(s "a"), exst!(s "b"), exst!(s "c")]
      })
    ]));

    parse_test!(r#"\(x){y}(1)"#, AST(vec![
      exst!(Call { f: bx!(ex!(m
        Lambda { 
          params: vec![(rc!(x), None)],
          type_anno: None,
          body: vec![exst!(s "y")] }
        )),
        arguments: vec![inv!(NatLiteral(1)).into()] })]));

    parse_test_wrap_ast! {
      r#"\(x: Int): String { "q" }"#,
      exst!(Lambda {
        params: vec![(rc!(x), Some(ty!("Int")))],
        type_anno: Some(ty!("String")),
        body: vec![exst!(s r#""q""#)]
      })
    }
  }

  #[test]
  fn single_param_lambda() {
    parse_test_wrap_ast! {
      r"\x { x + 10 }", 
      exst!(Lambda {
        params: vec![(rc!(x), None)],
        type_anno: None,
        body: vec![exst!(s r"x + 10")]
      })
    }

    parse_test_wrap_ast! {
      r"\x: Nat { x + 10 }", 
      exst!(Lambda {
        params: vec![(rc!(x), Some(ty!("Nat")))],
        type_anno: None,
        body: vec![exst!(s r"x + 10")]
      })
    }
  }

  #[test]
  fn more_advanced_lambdas() {
    parse_test! {
      r#"fn wahoo() { let a = 10; \(x) { x + a } };
      wahoo()(3) "#,  AST(vec![
        exst!(s r"fn wahoo() { let a = 10; \(x) { x + a } }"),
        exst! {
          Call {
            f: bx!(ex!(m Call { f: bx!(ex!(m val!("wahoo"))), arguments: vec![] })),
            arguments: vec![inv!(NatLiteral(3)).into()],
          }
        }
      ])
    }
  }

  #[test]
   fn list_literals() {
     parse_test! {
       "[1,2]", AST(vec![
         exst!(ListLiteral(vec![ex!(m NatLiteral(1)), ex!(m NatLiteral(2))]))])
     };
   }

  #[test]
  fn while_expr() {
    parse_test! {
      "while { }", AST(vec![
      exst!(WhileExpression { condition: None, body: vec![] })])
    }

    parse_test! {
      "while a == b { }", AST(vec![
      exst!(WhileExpression { condition: Some(bx![ex![m binexp!("==", val!("a"), val!("b"))]]), body: vec![] })])
    }
  }

  #[test]
  fn for_expr() {
    parse_test! {
      "for { a <- maybeValue } return 1", AST(vec![
      exst!(ForExpression {
        enumerators: vec![Enumerator { id: rc!(a), generator: ex!(m val!("maybeValue")) }],
        body: bx!(MonadicReturn(Meta::new(ex!(s "1"))))
      })])
    }

    parse_test! {
      "for n <- someRange { f(n); }", AST(vec![
      exst!(ForExpression { enumerators: vec![Enumerator { id: rc!(n), generator: ex!(m val!("someRange"))}],
        body: bx!(ForBody::StatementBlock(vec![exst!(s "f(n)")]))
      })])
    }
  }

  #[test]
  fn patterns() {
    parse_test_wrap_ast! {
      "if x is Some(a) then { 4 } else { 9 }", exst!(
        IfExpression {
          discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
          body: bx!(IfExpressionBody::SimplePatternMatch(Pattern::TupleStruct(rc!(Some), vec![Pattern::Literal(PatternLiteral::VarPattern(rc!(a)))]), vec![exst!(s "4")], Some(vec![exst!(s "9")]))) }
        )
    }

    parse_test_wrap_ast! {
      "if x is Some(a) then 4 else 9", exst!(
        IfExpression {
          discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
          body: bx!(IfExpressionBody::SimplePatternMatch(Pattern::TupleStruct(rc!(Some), vec![Pattern::Literal(PatternLiteral::VarPattern(rc!(a)))]), vec![exst!(s "4")], Some(vec![exst!(s "9")]))) }
      )
    }

    parse_test_wrap_ast! {
      "if x is Something { a, b: x } then { 4 } else { 9 }", exst!(
        IfExpression {
          discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
          body: bx!(IfExpressionBody::SimplePatternMatch(
              Pattern::Record(rc!(Something), vec![
                (rc!(a),Pattern::Literal(PatternLiteral::StringPattern(rc!(a)))),
                (rc!(b),Pattern::Literal(PatternLiteral::VarPattern(rc!(x)))) 
              ]),
              vec![exst!(s "4")], Some(vec![exst!(s "9")]))) 
        }
      )
    }
  }

  #[test]
  fn pattern_literals() {
    parse_test_wrap_ast! {
      "if x is -1 then 1 else 2",
      exst!(
        IfExpression {
          discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
          body: bx!(IfExpressionBody::SimplePatternMatch(
            Pattern::Literal(PatternLiteral::NumPattern { neg: true, num: NatLiteral(1) }),
            vec![exst!(NatLiteral(1))],
            Some(vec![exst!(NatLiteral(2))]),
          ))
        }
      )
    }

    parse_test_wrap_ast! {
      "if x is 1 then 1 else 2", 
      exst!(
        IfExpression {
          discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
          body: bx!(IfExpressionBody::SimplePatternMatch(
              Pattern::Literal(PatternLiteral::NumPattern { neg: false, num: NatLiteral(1) }),
              vec![exst!(s "1")],
              Some(vec![exst!(s "2")]),
              ))
        }
      )
    }

    parse_test! {
      "if x is true then 1 else 2", AST(vec![
        exst!(
          IfExpression {
            discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
            body: bx!(IfExpressionBody::SimplePatternMatch(
              Pattern::Literal(PatternLiteral::BoolPattern(true)),
              vec![exst!(NatLiteral(1))],
              Some(vec![exst!(NatLiteral(2))]),
            ))
          }
        )
      ])
    }

    parse_test_wrap_ast! {
      "if x is \"gnosticism\" then 1 else 2",
        exst!(
          IfExpression {
            discriminator: bx!(Discriminator::Simple(ex!(s "x"))),
            body: bx!(IfExpressionBody::SimplePatternMatch(
                Pattern::Literal(PatternLiteral::StringPattern(rc!(gnosticism))),
                vec![exst!(s "1")],
                Some(vec![exst!(s "2")]),
                ))
          }
        )
    }
  }
}