schala/src/schala_lang/parsing.rs

use itertools::Itertools;
use std::collections::HashMap;
use std::rc::Rc;
use std::iter::{Enumerate, Peekable};
use std::vec::IntoIter;
use std::str::Chars;

#[derive(Debug, PartialEq, Clone)]
pub enum TokenType {
  Newline, Semicolon,

  LParen, RParen,
  LSquareBracket, RSquareBracket,
  LAngleBracket, RAngleBracket,
  LCurlyBrace, RCurlyBrace,
  Pipe,

  Comma, Period, Colon, Underscore,

  Operator(Rc<String>),
  DigitGroup(Rc<String>), HexLiteral(Rc<String>), BinNumberSigil,
  StrLiteral(Rc<String>),
  Identifier(Rc<String>),
  Keyword(Kw),

  EOF,

  Error(String),
}
use self::TokenType::*;

#[derive(Debug, Clone, Copy, PartialEq)]
pub enum Kw {
  If, Else,
  Func,
  For,
  Match,
  Var, Const, Let, In,
  Return,
  Alias, Type, SelfType, SelfIdent,
  Trait, Impl,
  True, False,
  Module
}
use self::Kw::*;

lazy_static! {
  static ref KEYWORDS: HashMap<&'static str, Kw> =
    hashmap! {
      "if" => Kw::If,
      "else" => Kw::Else,
      "fn" => Kw::Func,
      "for" => Kw::For,
      "match" => Kw::Match,
      "var" => Kw::Var,
      "const" => Kw::Const,
      "let" => Kw::Let,
      "in" => Kw::In,
      "return" => Kw::Return,
      "alias" => Kw::Alias,
      "type" => Kw::Type,
      "Self" => Kw::SelfType,
      "self" => Kw::SelfIdent,
      "trait" => Kw::Trait,
      "impl" => Kw::Impl,
      "true" => Kw::True,
      "false" => Kw::False,
      "module" => Kw::Module,
    };
}

#[derive(Debug)]
pub struct Token {
  pub token_type: TokenType,
  pub offset: usize,
}

impl Token {
  pub fn get_error(&self) -> Option<&String> {
    match self.token_type {
      TokenType::Error(ref s) => Some(s),
      _ => None,
    }
  }
}

fn is_digit(c: &char) -> bool {
  c.is_digit(10)
}

const OPERATOR_CHARS: [char; 19] = ['!', '$', '%', '&', '*', '+', '-', '.', '/', ':', '<', '>', '=', '?', '@', '^', '|', '~', '`'];
fn is_operator(c: &char) -> bool {
  OPERATOR_CHARS.iter().any(|x| x == c)
}

type CharIter<'a> = Peekable<Enumerate<Chars<'a>>>;

pub fn tokenize(input: &str) -> Vec<Token> {
  let mut tokens: Vec<Token> = Vec::new();
  let mut input: CharIter = input.chars().enumerate().peekable();

  while let Some((idx, c)) = input.next() {
    let cur_tok_type = match c {
      '#' => {
        if let Some(&(_, '{')) = input.peek() {
        } else {
          while let Some((_, c)) = input.next() {
            if c == '\n' {
              break;
            }
          }
        }
        continue;
      },
      c if c.is_whitespace() && c != '\n' => continue,
      '\n' => Newline, ';' => Semicolon,
      ':' => Colon, ',' => Comma,
      '(' => LParen, ')' => RParen,
      '{' => LCurlyBrace, '}' => RCurlyBrace,
      '[' => LSquareBracket, ']' => RSquareBracket,
      '"' => handle_quote(&mut input),
      c if is_digit(&c) => handle_digit(c, &mut input),
      c if c.is_alphabetic() || c == '_' => handle_alphabetic(c, &mut input), //TODO I'll probably have to rewrite this if I care about types being uppercase, also type parameterization
      c if is_operator(&c) => handle_operator(c, &mut input),
      unknown => Error(format!("Unexpected character: {}", unknown)),
    };
    tokens.push(Token { token_type: cur_tok_type, offset: idx });
  }
  tokens
}

fn handle_digit(c: char, input: &mut CharIter) -> TokenType {
  if c == '0' && input.peek().map_or(false, |&(_, c)| { c == 'x' }) {
    input.next();
    let rest: String = input.peeking_take_while(|&(_, ref c)| c.is_digit(16) || *c == '_').map(|(_, c)| { c }).collect();
    HexLiteral(Rc::new(rest))
  } else if c == '0' && input.peek().map_or(false, |&(_, c)| { c == 'b' }) {
    input.next();
    BinNumberSigil
  } else {
    let mut buf = c.to_string();
    buf.extend(input.peeking_take_while(|&(_, ref c)| is_digit(c)).map(|(_, c)| { c }));
    DigitGroup(Rc::new(buf))
  }
}

fn handle_quote(input: &mut CharIter) -> TokenType {
  let mut buf = String::new();
  loop {
    match input.next().map(|(_, c)| { c }) {
      Some('"') => break,
      Some('\\') => {
        let next = input.peek().map(|&(_, c)| { c });
        if next == Some('n') {
          input.next();
          buf.push('\n')
        } else if next == Some('"') {
          input.next();
          buf.push('"');
        } else if next == Some('t') {
          input.next();
          buf.push('\t');
        }
      },
      Some(c) => buf.push(c),
      None => return TokenType::Error(format!("Unclosed string")),
    }
  }
  TokenType::StrLiteral(Rc::new(buf))
}

fn handle_alphabetic(c: char, input: &mut CharIter) -> TokenType {
  let mut buf = String::new();
  buf.push(c);
  if c == '_' && input.peek().map(|&(_, c)| { !c.is_alphabetic() }).unwrap_or(true) {
    return TokenType::Underscore
  }

  loop {
    match input.peek().map(|&(_, c)| { c }) {
      Some(c) if c.is_alphanumeric() => {
        input.next();
        buf.push(c);
      },
      _ => break,
    }
  }

  match KEYWORDS.get(buf.as_str()) {
    Some(kw) => TokenType::Keyword(kw.clone()),
    None => TokenType::Identifier(Rc::new(buf)),
  }
}

fn handle_operator(c: char, input: &mut CharIter) -> TokenType {
  match c {
    '<' | '>' | '|' | '.' => {
      let ref next = input.peek().map(|&(_, c)| { c });
      if !next.map(|n| { is_operator(&n) }).unwrap_or(false) {
        return match c {
          '<' => LAngleBracket,
          '>' => RAngleBracket,
          '|' => Pipe,
          '.' => Period,
          _ => unreachable!(),
        }
      }
    },
    _ => (),
  };

  let mut buf = String::new();
  buf.push(c);
  loop {
    match input.peek().map(|&(_, c)| { c }) {
      Some(c) if is_operator(&c) => {
        input.next();
        buf.push(c);
      },
      _ => break
    }
  }
  TokenType::Operator(Rc::new(buf))
}

#[cfg(test)]
mod schala_tokenizer_tests {
  use super::*;

  macro_rules! digit { ($ident:expr) => { DigitGroup(Rc::new($ident.to_string())) } }
  macro_rules! ident { ($ident:expr) => { Identifier(Rc::new($ident.to_string())) } }
  macro_rules! op { ($ident:expr) => { Operator(Rc::new($ident.to_string())) } }


  #[test]
  fn tokens() {
    let a = tokenize("let a: A<B> = c ++ d");
    let token_types: Vec<TokenType> = a.into_iter().map(move |t| t.token_type).collect();
    assert_eq!(token_types, vec![Keyword(Let), ident!("a"), Colon, ident!("A"),
      LAngleBracket, ident!("B"), RAngleBracket, op!("="), ident!("c"), op!("++"), ident!("d")]);
  }

  #[test]
  fn underscores() {
    let token_types: Vec<TokenType> = tokenize("4_8").into_iter().map(move |t| t.token_type).collect();
    assert_eq!(token_types, vec![digit!("4"), Underscore, digit!("8")]);
  }
}

/* Schala EBNF Grammar */
/* Terminal productions are in 'single quotes' or UPPERCASE if they are a class
 * or not representable in ASCII

program := (statement delimiter)* EOF
delimiter := NEWLINE | ';'
statement := expression | declaration

declaration := type_declaration | func_declaration | binding_declaration | impl_declaration

type_declaration := 'type' type_declaration_body
type_declaration_body := 'alias' type_alias | IDENTIFIER '=' 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

func_declaration := func_signature func_body
func_body := ε | '{' (statement delimiter)* '}'
func_signature := 'fn' IDENTIFIER formal_param_list func_body
formal_param_list := '(' (formal_param ',')* ')'
formal_param := IDENTIFIER type_anno+

binding_declaration: 'var' IDENTIFIER '=' expression
                      | 'const' IDENTIFIER '=' expression

trait_declaration := 'trait' trait_name decl_block
impl_declaration := 'impl' IDENTIFIER decl_block | 'impl' trait_name 'for' IDENTIFIER decl_block

decl_block := '{' (func_declaration)* '}'

trait_name := IDENTIFIER

type_anno := (':' type_name)+
type_name := IDENTIFIER (type_params)* | '(' type_names ')'
type_names := ε | type_name (, type_name)*
type_params := '<' type_name (, type_name)* '>'

expression := precedence_expr type_anno+

precedence_expr := prefix_expr
prefix_expr := prefix_op primary
prefix_op := '+' | '-' | '!' | '~'
primary := literal | paren_expr | if_expr | match_expr | for_expr | identifier_expr

paren_expr := LParen paren_inner RParen
paren_inner := (expression ',')*
identifier_expr := named_struct | call_expr | index_expr | IDENTIFIER
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

if_expr := 'if' expression block else_clause
else_clause := ε | 'else' block

match_expr := 'match' expression match_body
match_body := '{' (match_arm)* '}'
match_arm := pattern '=>' expression
pattern := identifier //TODO NOT DONE

block := '{' (statement)* '}'

call_expr := IDENTIFIER '(' expr_list ')' //TODO maybe make this optional? or no, have a bare identifier meant to be used as method taken care of in eval
index_expr := '[' (expression (',' (expression)* | ε) ']'
expr_list := expression (',' expression)* | ε

for_expr := 'for' ... ????

// a float_literal can still be assigned to an int in type-checking
number_literal := int_literal | float_literal
int_literal = ('0x' | '0b') digits
float_literal := digits ('.' digits)
digits := (DIGIT_GROUP underscore)+

*/

type TokenIter = Peekable<IntoIter<Token>>;

#[derive(Debug, PartialEq)]
pub struct ParseError {
  pub msg: String,
}

impl ParseError {
  fn new<T>(msg: &str) -> ParseResult<T> {
    Err(ParseError { msg: msg.to_string() })
  }
}

pub type ParseResult<T> = Result<T, ParseError>;

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

struct Parser {
  tokens: TokenIter,
  parse_record: Vec<ParseRecord>,
  parse_level: u32
}

impl Parser {
  fn new(input: Vec<Token>) -> Parser {
    Parser { tokens: input.into_iter().peekable(), parse_record: vec![], parse_level: 0 }
  }

  fn peek(&mut self) -> TokenType {
    self.tokens.peek().map(|ref t| { t.token_type.clone() }).unwrap_or(TokenType::EOF)
  }

  fn next(&mut self) -> TokenType {
    self.tokens.next().map(|ref t| { t.token_type.clone() }).unwrap_or(TokenType::EOF)
  }
}

macro_rules! expect {
  ($self:expr, $token_type:pat, $expected_item:expr) => { expect!($self, $token_type if true, $expected_item) };
  ($self:expr, $token_type:pat if $cond:expr, $expected_item:expr) => {
    match $self.peek() {
      $token_type if $cond => $self.next(),
      tok => {
        let msg = format!("Expected {}, got {:?}", $expected_item, tok);
        return Err(ParseError { msg })
      }
    }
  }
}

#[derive(Debug, PartialEq)]
pub struct AST(pub Vec<Statement>);

#[derive(Debug, PartialEq, Clone)]
pub enum Statement {
  ExpressionStatement(Expression),
  Declaration(Declaration),
}

type ParamName = Rc<String>;
type TraitName = Rc<String>;
type FormalParam = (ParamName, Option<TypeName>);

#[derive(Debug, PartialEq, Clone)]
pub enum Declaration {
  FuncSig(Signature),
  FuncDecl(Signature, Vec<Statement>),
  TypeDecl(Rc<String>, TypeBody),
  TypeAlias(Rc<String>, Rc<String>),
  Binding {
    name: Rc<String>,
    constant: bool,
    expr: Expression,
  },
  Impl {
    type_name: TypeName,
    trait_name: Option<TraitName>,
    block: Vec<Declaration>,
  },
}

#[derive(Debug, PartialEq, Clone)]
pub struct Signature {
  pub name: Rc<String>,
  pub params: Vec<FormalParam>,
  pub type_anno: Option<TypeName>,
}

#[derive(Debug, PartialEq, Clone)]
pub struct TypeBody(pub Vec<Variant>);

#[derive(Debug, PartialEq, Clone)]
pub enum Variant {
  UnitStruct(Rc<String>),
  TupleStruct(Rc<String>, Vec<TypeName>),
  Record(Rc<String>, Vec<(Rc<String>, TypeName)>),
}

#[derive(Debug, PartialEq, Clone)]
pub struct Expression(pub ExpressionType, pub Option<TypeName>);

#[derive(Debug, PartialEq, Clone)]
pub enum TypeName {
  Tuple(Vec<TypeName>),
  Singleton {
    name: Rc<String>,
    params: Vec<TypeName>,
  }
}

#[derive(Debug, PartialEq, Clone)]
pub enum ExpressionType {
  IntLiteral(u64),
  FloatLiteral(f64),
  StringLiteral(Rc<String>),
  BoolLiteral(bool),
  BinExp(Operation, Box<Expression>, Box<Expression>),
  PrefixExp(Operation, Box<Expression>),
  TupleLiteral(Vec<Expression>),
  Value(Rc<String>, Vec<(Rc<String>, Expression)>),
  Call {
    f: Box<Expression>,
    arguments: Vec<Expression>,
  },
  Index {
    indexee: Box<Expression>,
    indexers: Vec<Expression>,
  },
  IfExpression(Box<Expression>, Vec<Statement>, Option<Vec<Statement>>),
  MatchExpression(Box<Expression>, Vec<MatchArm>),
  ForExpression
}

#[derive(Debug, PartialEq, Clone)]
pub struct MatchArm {
  pat: Pattern,
  expr: Expression,
}

#[derive(Debug, PartialEq, Clone)]
pub struct Pattern(Rc<String>);

#[derive(Debug, PartialEq, Clone)]
pub struct Operation(pub Rc<String>);

impl Operation {
  fn min_precedence() -> i32 {
    i32::min_value()
  }

  fn get_precedence(op: &str) -> i32 {
    match op {
      "+" | "-" => 10,
      "*" | "/" | "%" =>  20,
      _ => 30,
    }
  }

  fn is_prefix(op: &str) -> bool {
    match op {
      "+" | "-" | "!" | "~" => true,
      _ => false,
    }
  }
}

macro_rules! parse_method {
  ($name:ident(&mut $self:ident) -> $type:ty $body:block) => {
    fn $name(&mut $self) -> $type {
      let next_token = $self.peek();
      let record = ParseRecord {
        production_name: stringify!($name).to_string(),
        next_token: format!("{:?}", next_token),
        level: $self.parse_level,
      };
      $self.parse_level += 1;
      $self.parse_record.push(record);
      let result = { $body };

      if $self.parse_level != 0 {
        $self.parse_level -= 1;
      }
      result
    }
  };
}

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

impl Parser {
  parse_method!(program(&mut self) -> ParseResult<AST> {
    let mut statements = Vec::new();
    loop {
      match self.peek() {
        EOF => break,
        Newline | Semicolon => {
          self.next();
          continue;
        },
        _ => statements.push(self.statement()?),
      }
    }
    Ok(AST(statements))
  });

  parse_method!(statement(&mut self) -> ParseResult<Statement> {
    //TODO handle error recovery here
    match self.peek() {
      Keyword(Type) => self.type_declaration().map(|decl| { Statement::Declaration(decl) }),
      Keyword(Func)=> self.func_declaration().map(|func| { Statement::Declaration(func) }),
      Keyword(Var) | Keyword(Const) => self.binding_declaration().map(|decl| Statement::Declaration(decl)),
      Keyword(Trait) => self.trait_declaration().map(|decl| Statement::Declaration(decl)),
      Keyword(Impl) => self.impl_declaration().map(|decl| Statement::Declaration(decl)),
      _ => self.expression().map(|expr| { Statement::ExpressionStatement(expr) } ),
    }
  });

  parse_method!(type_declaration(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Type), "'type'");
    self.type_declaration_body()
  });

  parse_method!(type_declaration_body(&mut self) -> ParseResult<Declaration> {
    if let Keyword(Alias) = self.peek() {
      self.type_alias()
    } else {
      let name = self.identifier()?;
      expect!(self, Operator(ref c) if **c == "=", "'='");
      let body = self.type_body()?;
      Ok(Declaration::TypeDecl(name, body))
    }
  });

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

  parse_method!(type_body(&mut self) -> ParseResult<TypeBody> {
    let mut variants = Vec::new();
    variants.push(self.variant_specifier()?);
    loop {
      if let Pipe = self.peek() {
        self.next();
        variants.push(self.variant_specifier()?);
      } else {
        break;
      }
    }
    Ok(TypeBody(variants))
  });

  parse_method!(variant_specifier(&mut self) -> ParseResult<Variant> {
    use self::Variant::*;

    let name = self.identifier()?;
    match self.peek() {
      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, typed_identifier_list))
      },
      _ => Ok(UnitStruct(name))
    }
  });

  parse_method!(typed_identifier(&mut self) -> ParseResult<(Rc<String>, TypeName)> {
    let identifier = self.identifier()?;
    expect!(self, Colon, "':'");
    let type_name = self.type_name()?;
    Ok((identifier, type_name))
  });

  parse_method!(func_declaration(&mut self) -> ParseResult<Declaration> {
    let signature = self.signature()?;
    if let LCurlyBrace = self.peek() {
      let statements = delimited!(self, LCurlyBrace, '{', statement, Newline | Semicolon, RCurlyBrace, '}');
      Ok(Declaration::FuncDecl(signature, statements))
    } else {
      Ok(Declaration::FuncSig(signature))
    }
  });

  parse_method!(signature(&mut self) -> ParseResult<Signature> {
    expect!(self, Keyword(Func), "'fn'");
    let name = self.identifier()?;
    let params = delimited!(self, LParen, '(', formal_param, Comma, RParen, ')');
    let type_anno = match self.peek() {
      Colon => Some(self.type_anno()?),
      _ => None,
    };
    Ok(Signature { name, params, type_anno })
  });

  parse_method!(formal_param(&mut self) -> ParseResult<FormalParam> {
    let name = self.identifier()?;
    let ty = match self.peek() {
      Colon => Some(self.type_anno()?),
      _ => None
    };
    Ok((name, ty))
  });

  parse_method!(binding_declaration(&mut self) -> ParseResult<Declaration> {
    let constant = match self.next() {
      Keyword(Var) => false,
      Keyword(Const) => true,
      _ => return ParseError::new("Expected 'var' or 'const'"),
    };
    let name = self.identifier()?;
    expect!(self, Operator(ref o) if **o == "=", "'='");
    let expr = self.expression()?;

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

  parse_method!(trait_declaration(&mut self) -> ParseResult<Declaration> {
    unimplemented!()
  });

  parse_method!(impl_declaration(&mut self) -> ParseResult<Declaration> {
    expect!(self, Keyword(Impl), "'impl'");
    let first = self.type_name()?;
    let second = if let Keyword(For) = self.peek() {
      self.next();
      Some(self.type_name()?)
    } else {
      None
    };

    let block = self.decl_block()?;

    let result = match (first, second) {
      (first, Some(second)) => {
        match first {
          TypeName::Singleton { ref name, ref params } if params.len() == 0 =>
            Declaration::Impl { type_name: second, trait_name: Some(name.clone()), block },
          _ => return ParseError::new(&format!("Invalid name for a trait")),
        }
      },
      (first, None) => Declaration::Impl { type_name: first, trait_name: None, block }
    };
    Ok(result)
  });

  parse_method!(decl_block(&mut self) -> ParseResult<Vec<Declaration>> {
    Ok(delimited!(self, LCurlyBrace, '{', func_declaration, Newline | Semicolon, RCurlyBrace, '}', nonstrict))
  });

  parse_method!(expression(&mut self) -> ParseResult<Expression> {
    let mut expr_body = self.precedence_expr(Operation::min_precedence())?;
    let type_anno = match self.peek() {
      Colon => Some(self.type_anno()?),
      _ => None
    };
    if let Some(_) = expr_body.1 {
      return ParseError::new("Bad parse state");
    }
    expr_body.1 = type_anno;
    Ok(expr_body)
  });

  parse_method!(type_anno(&mut self) -> ParseResult<TypeName> {
    expect!(self, Colon, "':'");
    self.type_name()
  });

  parse_method!(type_name(&mut self) -> ParseResult<TypeName> {
    use self::TypeName::*;
    Ok(match self.peek() {
      LParen => Tuple(delimited!(self, LParen, '(', type_name, Comma, RParen, ')')),
      _ => Singleton {
        name: self.identifier()?,
        params: match self.peek() {
          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 next_token = self.peek();
    let record = ParseRecord {
      production_name: "precedence_expr".to_string(),
      next_token: format!("{:?}", next_token),
      level: self.parse_level,
    };
    self.parse_level += 1;
    self.parse_record.push(record);

    let mut lhs = self.prefix_expr()?;
    loop {
      let new_precedence = match self.peek() {
        Operator(op) => Operation::get_precedence(&*op),
        Period => Operation::get_precedence("."),
        _ => break,
      };

      if precedence >= new_precedence {
        break;
      }
      let op_str = match self.next() {
        Operator(op) => op,
        Period => Rc::new(".".to_string()),
        _ => unreachable!(),
      };
      let rhs = self.precedence_expr(new_precedence)?;
      let operation = Operation(op_str);
      lhs = Expression(ExpressionType::BinExp(operation, Box::new(lhs), Box::new(rhs)), None);
    }
    self.parse_level -= 1;
    Ok(lhs)
  }

  parse_method!(prefix_expr(&mut self) -> ParseResult<Expression> {
    match self.peek() {
      Operator(ref op) if Operation::is_prefix(&*op) => {
        let op_str = match self.next() {
          Operator(op) => op,
          _ => unreachable!(),
        };
        let expr = self.primary()?;
        Ok(Expression(
            ExpressionType::PrefixExp(Operation(op_str), Box::new(expr)),
            None))
      },
      _ => self.primary()
    }
  });

  parse_method!(primary(&mut self) -> ParseResult<Expression> {
    match self.peek() {
      LParen => self.paren_expr(),
      Keyword(Kw::If) => self.if_expr(),
      Keyword(Kw::Match) => self.match_expr(),
      Keyword(Kw::For) => self.for_expr(),
      Identifier(_) => self.identifier_expr(),
      _ => self.literal(),
    }
  });

  parse_method!(paren_expr(&mut self) -> ParseResult<Expression> {
    use self::ExpressionType::*;
    let mut inner = delimited!(self, LParen, '(', expression, Comma, RParen, ')');
    match inner.len() {
      0 => Ok(Expression(TupleLiteral(vec![]), None)),
      1 => Ok(inner.pop().unwrap()),
      _ => Ok(Expression(TupleLiteral(inner), None)),
    }
  });

  parse_method!(identifier_expr(&mut self) -> ParseResult<Expression> {
    use self::ExpressionType::*;
    let identifier = self.identifier()?;
    Ok(match self.peek() {
      LCurlyBrace => {
        let fields = self.record_block()?;
        Expression(Value(identifier, fields), None)
      },
      LParen => {
        let arguments = self.call_expr()?;
        //TODO make this be more general
        let f = Box::new(Expression(Value(identifier, vec![]), None));
        Expression(Call { f, arguments }, None)
      },
      LSquareBracket => {
        let indexers = self.index_expr()?;
        Expression(Index {
          indexee: Box::new(Expression(Value(identifier, vec![]), None)),
          indexers,
        }, None)
      }
      _ => Expression(Value(identifier, vec![]), None)
    })
  });

  parse_method!(record_block(&mut self) -> ParseResult<Vec<(Rc<String>, Expression)>> {
    Ok(delimited!(self, LCurlyBrace, '{', record_entry, Comma, RCurlyBrace, '}'))
  });

  parse_method!(record_entry(&mut self) -> ParseResult<(Rc<String>, Expression)> {
    let field_name = self.identifier()?;
    expect!(self, Colon, ":");
    let value = self.expression()?;
    Ok((field_name, value))
  });

  parse_method!(call_expr(&mut self) -> ParseResult<Vec<Expression>> {
    Ok(delimited!(self, LParen, ')', expression, Comma, RParen, '('))
  });

  parse_method!(index_expr(&mut self) -> ParseResult<Vec<Expression>> {
    Ok(delimited!(self, LSquareBracket, '[', expression, Comma, RSquareBracket, ']'))
  });

  parse_method!(if_expr(&mut self) -> ParseResult<Expression> {
    expect!(self, Keyword(Kw::If), "'if'");
    let condition = self.expression()?;
    let then_clause = self.block()?;
    let else_clause = self.else_clause()?;
    Ok(Expression(ExpressionType::IfExpression(Box::new(condition), then_clause, else_clause), None))
  });

  parse_method!(else_clause(&mut self) -> ParseResult<Option<Vec<Statement>>> {
    Ok(if let Keyword(Kw::Else) = self.peek() {
      self.next();
      Some(self.block()?)
    } else {
      None
    })
  });

  parse_method!(block(&mut self) -> ParseResult<Vec<Statement>> {
    Ok(delimited!(self, LCurlyBrace, '{', statement, Newline | Semicolon, RCurlyBrace, '}', nonstrict))
  });

  parse_method!(match_expr(&mut self) -> ParseResult<Expression> {
    expect!(self, Keyword(Kw::Match), "'match'");
    let expr = self.expression()?;
    //TODO abstract these errors into the delimited macro
    //expect!(self, LCurlyBrace, "Expected '{'");
    let body = self.match_body()?;
    //expect!(self, RCurlyBrace, "Expected '}'");
    Ok(Expression(ExpressionType::MatchExpression(Box::new(expr), body), None))
  });

  parse_method!(match_body(&mut self) -> ParseResult<Vec<MatchArm>> {
    Ok(delimited!(self, LCurlyBrace, '{', match_arm, Comma, RCurlyBrace, '}'))
  });

  parse_method!(match_arm(&mut self) -> ParseResult<MatchArm> {
    let pat = self.pattern()?;
    expect!(self, Operator(ref c) if **c == "=>", "'=>'");
    let expr = self.expression()?;
    Ok(MatchArm { pat, expr })
  });

  parse_method!(pattern(&mut self) -> ParseResult<Pattern> {
    let identifier = self.identifier()?;
    Ok(Pattern(identifier))
  });

  parse_method!(for_expr(&mut self) -> ParseResult<Expression> {
    expect!(self, Keyword(Kw::For), "'for'");
    Ok(Expression(ExpressionType::ForExpression, None))
  });

  parse_method!(identifier(&mut self) -> ParseResult<Rc<String>> {
    match self.next() {
      Identifier(s) => Ok(s),
      p => ParseError::new(&format!("Expected an identifier, got {:?}", p)),
    }
  });

  parse_method!(literal(&mut self) -> ParseResult<Expression> {
    use self::ExpressionType::*;
    match self.peek() {
      DigitGroup(_) | HexLiteral(_) | BinNumberSigil | Period => self.number_literal(),
      Keyword(Kw::True) => {
        self.next();
        Ok(Expression(BoolLiteral(true), None))
      },
      Keyword(Kw::False) => {
        self.next();
        Ok(Expression(BoolLiteral(false), None))
      },
      StrLiteral(s) => {
        self.next();
        Ok(Expression(StringLiteral(s), None))
      }
      e => ParseError::new(&format!("Expected a literal expression, got {:?}", e)),
    }
  });

  parse_method!(number_literal(&mut self) -> ParseResult<Expression> {
    match self.peek() {
      HexLiteral(_) | BinNumberSigil => self.int_literal(),
      _ => self.float_literal(),
    }
  });

  parse_method!(int_literal(&mut self) -> ParseResult<Expression> {
    use self::ExpressionType::*;
    match self.next() {
      BinNumberSigil => {
        let digits = self.digits()?;
        let n = parse_binary(digits)?;
        Ok(Expression(IntLiteral(n), None))
      },
      HexLiteral(text) => {
        let digits: String = text.chars().filter(|c| c.is_digit(16)).collect();
        let n = parse_hex(digits)?;
        Ok(Expression(IntLiteral(n), None))
      },
      _ => return ParseError::new("Expected '0x' or '0b'"),
    }
  });

  parse_method!(float_literal(&mut self) -> ParseResult<Expression> {
    use self::ExpressionType::*;
    let mut digits = self.digits()?;
    if let TokenType::Period = self.peek() {
      self.next();
      digits.push_str(".");
      digits.push_str(&self.digits()?);
      match digits.parse::<f64>() {
        Ok(f) => Ok(Expression(FloatLiteral(f), None)),
        Err(e) => ParseError::new(&format!("Float failed to parse with error: {}", e)),

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

  parse_method!(digits(&mut self) -> ParseResult<String> {
    let mut ds = String::new();
    loop {
      match self.peek() {
        Underscore => { self.next(); continue; },
        DigitGroup(ref s) => { self.next(); ds.push_str(s)},
        _ => break,
      }
    }
    Ok(ds)
  });
}

fn parse_binary(digits: String) -> 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("Encountered a character not '1' or '0 while parsing a binary literal"),
    }
    multiplier *= 2;
  }
  Ok(result)
}

fn parse_hex(digits: String) -> 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("Encountered a non-hex digit in a hex literal"),
    }
    multiplier *= 16;
  }
  Ok(result)
}

pub fn parse(input: Vec<Token>) -> (Result<AST, ParseError>, Vec<String>) {
  let mut parser = Parser::new(input);
  let ast = parser.program();

  let trace = parser.parse_record.into_iter().map(|r| {
    let mut indent = String::new();
    for i in 0..r.level {
      indent.push(' ');
    }
    format!("{}Production `{}`, token: {:?}", indent, r.production_name, r.next_token)
  }).collect();
  (ast, trace)
}

#[cfg(test)]
mod parse_tests {
  use ::std::rc::Rc;
  use super::{AST, Expression, Statement, Operation, TypeBody, Variant, parse, tokenize};
  use super::Statement::*;
  use super::Declaration::*;
  use super::Signature;
  use super::TypeName::*;
  use super::ExpressionType::*;
  use super::Variant::*;

  macro_rules! rc {
    ($string:tt) => { Rc::new(stringify!($string).to_string()) }
  }
  macro_rules! parse_test {
    ($string:expr, $correct:expr) => { assert_eq!(parse(tokenize($string)).0.unwrap(), $correct) }
  }
  macro_rules! parse_error {
    ($string:expr) => { assert!(parse(tokenize($string)).0.is_err()) }
  }
  macro_rules! binexp {
    ($op:expr, $lhs:expr, $rhs:expr) => { BinExp(op!($op), Box::new(Expression($lhs, None)), Box::new(Expression($rhs, None))) }
  }
  macro_rules! prefexp {
    ($op:expr, $lhs:expr) => { PrefixExp(op!($op), Box::new(Expression($lhs, None))) }
  }
  macro_rules! op {
    ($op:expr) => { Operation(Rc::new($op.to_string())) }
  }
  macro_rules! val {
    ($var:expr) => { Value(Rc::new($var.to_string()), vec![]) }
  }
  macro_rules! exprstatement {
    ($expr_type:expr) => { Statement::ExpressionStatement(Expression($expr_type, None)) };
    ($expr_type:expr, $type_anno:expr) => { Statement::ExpressionStatement(Expression($expr_type, Some($type_anno))) };
  }
  macro_rules! ex {
    ($expr_type:expr) => { Expression($expr_type, None) }
  }
  macro_rules! ty {
    ($name:expr) => { Singleton { name: Rc::new($name.to_string()), params: vec![] } };
  }

  #[test]
  fn parsing_number_literals_and_binexps() {
    parse_test!(".2", AST(vec![exprstatement!(FloatLiteral(0.2))]));
    parse_test!("8.1", AST(vec![exprstatement!(FloatLiteral(8.1))]));

    parse_test!("0b010", AST(vec![exprstatement!(IntLiteral(2))]));
    parse_test!("0b0_1_0_", AST(vec![exprstatement!(IntLiteral(2))]));

    parse_test!("0xff", AST(vec![exprstatement!(IntLiteral(255))]));
    parse_test!("0xf_f_", AST(vec![exprstatement!(IntLiteral(255))]));

    parse_test!("0xf_f_+1", AST(vec![exprstatement!(binexp!("+", IntLiteral(255), IntLiteral(1)))]));

    parse_test!("3; 4; 4.3", AST(
      vec![exprstatement!(IntLiteral(3)), exprstatement!(IntLiteral(4)),
        exprstatement!(FloatLiteral(4.3))]));

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

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

    parse_test!("1 && 2", AST(vec![exprstatement!(binexp!("&&", IntLiteral(1), IntLiteral(2)))]));

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

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

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

  #[test]
  fn parsing_tuples() {
    parse_test!("()", AST(vec![exprstatement!(TupleLiteral(vec![]))]));
    parse_test!("(\"hella\", 34)", AST(vec![exprstatement!(
      TupleLiteral(
        vec![ex!(StringLiteral(rc!(hella))), ex!(IntLiteral(34))]
      )
    )]));
    parse_test!("((1+2), \"slough\")", AST(vec![exprstatement!(TupleLiteral(vec![
      ex!(binexp!("+", IntLiteral(1), IntLiteral(2))),
      ex!(StringLiteral(rc!(slough))),
    ]))]))
  }

  #[test]
  fn parsing_identifiers() {
    parse_test!("a", AST(vec![exprstatement!(val!("a"))]));
    parse_test!("a + b", AST(vec![exprstatement!(binexp!("+", val!("a"), val!("b")))]));
    //parse_test!("a[b]", AST(vec![Expression(
    //parse_test!("a[]", <- TODO THIS NEEDS TO FAIL
    //parse_test!(damn()[a] ,<- TODO needs to succeed
    parse_test!("a[b,c]", AST(vec![exprstatement!(Index { indexee: Box::new(ex!(val!("a"))), indexers: vec![ex!(val!("b")), ex!(val!("c"))]} )]));     

    parse_test!("None", AST(vec![exprstatement!(val!("None"))]));
    parse_test!("Pandas {  a: x + y }", AST(vec![
      exprstatement!(Value(rc!(Pandas), vec![(rc!(a), ex!(binexp!("+", val!("x"), val!("y"))))]))]));
  }

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

  #[test]
  fn parsing_functions() {
    parse_test!("fn oi()",  AST(vec![Declaration(FuncSig(Signature { name: rc!(oi), params: vec![], type_anno: None }))]));
    parse_test!("oi()", AST(vec![exprstatement!(Call { f: Box::new(ex!(val!("oi"))), arguments: vec![] })]));
    parse_test!("oi(a, 2 + 2)", AST(vec![exprstatement!(Call
    { f: Box::new(ex!(val!("oi"))),
      arguments: vec![ex!(val!("a")), ex!(binexp!("+", IntLiteral(2), IntLiteral(2)))]
    })]));
    parse_error!("a(b,,c)");

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


    parse_test!("fn a(x) { x() }", AST(vec![Declaration(
      FuncDecl(Signature { name: rc!(a), params: vec![(rc!(x),None)], type_anno: None },
        vec![exprstatement!(Call { f: Box::new(ex!(val!("x"))), arguments: vec![] })]))]));
  }

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

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

  #[test]
  fn parsing_types() {
    parse_test!("type Yolo = Yolo", AST(vec![Declaration(TypeDecl(rc!(Yolo), TypeBody(vec![UnitStruct(rc!(Yolo))])))]));
    parse_test!("type alias Sex = Drugs", AST(vec![Declaration(TypeAlias(rc!(Sex), rc!(Drugs)))]));
    parse_test!("type Sanchez = Miguel | Alejandro(Int, Option<a>) | Esparanza { a: Int, b: String }",
      AST(vec![Declaration(TypeDecl(rc!(Sanchez), TypeBody(vec![
        UnitStruct(rc!(Miguel)),
        TupleStruct(rc!(Alejandro), vec![
          Singleton { name: rc!(Int), params: vec![] },
          Singleton { name: rc!(Option), params: vec![Singleton { name: rc!(a), params: vec![] }] },
        ]),
        Record(rc!(Esparanza), vec![
          (rc!(a), Singleton { name: rc!(Int), params: vec![] }),
          (rc!(b), Singleton { name: rc!(String), params: vec![] }),
        ])])))]));
  }

  #[test]
  fn parsing_bindings() {
    parse_test!("var a = 10", AST(vec![Declaration(Binding { name: rc!(a), constant: false, expr: ex!(IntLiteral(10)) } )]));
    parse_test!("const a = 2 + 2", AST(vec![Declaration(Binding { name: rc!(a), constant: true, expr: ex!(binexp!("+", IntLiteral(2), IntLiteral(2))) }) ]));
  }

  #[test]
  fn parsing_block_expressions() {
    parse_test!("if a() { b(); c() }", AST(vec![exprstatement!(
        IfExpression(Box::new(ex!(Call { f: Box::new(ex!(val!("a"))), arguments: vec![]})),
          vec![exprstatement!(Call { f: Box::new(ex!(val!("b"))), arguments: vec![]}), exprstatement!(Call { f: Box::new(ex!(val!("c"))), arguments: vec![] })],
          None)
        )]));
    parse_test!(r#"
    if true {
      const a = 10
      b
    } else {
      c
    }"#,
    AST(vec![exprstatement!(IfExpression(Box::new(ex!(BoolLiteral(true))),
      vec![Declaration(Binding { name: rc!(a), constant: true, expr: ex!(IntLiteral(10)) }),
           exprstatement!(Value(rc!(b), vec![]))],
      Some(vec![exprstatement!(Value(rc!(c), vec![]))])))])
    );
  }

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

    parse_test!("impl Mondai for Lollerino { fn yolo(); fn swagg(); }", AST(vec![
      Declaration(Impl {
        type_name: ty!("Lollerino"),
        trait_name: Some(rc!(Mondai)),
        block: vec![
          FuncSig(Signature { name: rc!(yolo), params: vec![], type_anno: None}),
          FuncSig(Signature { name: rc!(swagg), params: vec![], type_anno: None })
        ] })]));
    parse_test!("impl Option<WTFMate> { fn oi() }", AST(vec![
      Declaration(Impl {
        type_name: Singleton { name: rc!(Option), params: vec![ty!("WTFMate")]},
        trait_name: None,
        block: vec![
          FuncSig(Signature { name: rc!(oi), params: vec![], type_anno: None }),
        ]
      })]));
  }

  #[test]
  fn parsing_type_annotations() {
    parse_test!("const a = b : Int", AST(vec![
      Declaration(Binding { name: rc!(a), constant: true, expr:
        Expression(val!("b"), Some(ty!("Int"))) })]));

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

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

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

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