From 744ba2fc749fea0a3b0682487d4fad0aaa1c2eb7 Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Mon, 9 Mar 2020 03:45:03 -0700
Subject: [PATCH] if expression

---
 schala-lang/language/src/parser.rs | 76 ++++++++++++++++++++++--------
 1 file changed, 57 insertions(+), 19 deletions(-)

diff --git a/schala-lang/language/src/parser.rs b/schala-lang/language/src/parser.rs
index 5d4fbe4..aef1122 100644
--- a/schala-lang/language/src/parser.rs
+++ b/schala-lang/language/src/parser.rs
@@ -6,7 +6,7 @@ use std::str::FromStr;
 use nom::IResult;
 use nom::character::complete::{one_of, space0, alphanumeric0};
 use nom::bytes::complete::{tag, take, take_while, take_while1, take_until};
-use nom::combinator::{cut, map, map_res, value, opt, verify};
+use nom::combinator::{cut, cond, map, map_res, value, opt, verify};
 use nom::multi::{separated_list, separated_nonempty_list, many1, many0};
 use nom::error::{context, ParseError, VerboseError};
 use nom::branch::alt;
@@ -51,10 +51,15 @@ fn identifier(text: &str) -> ParseResult<Rc<String>> {
 }
 
 const OPERATOR_CHARS: &'static str = "~`!@#$%^&*-+=<>?/|";
-fn parse_binop(text: &str) -> ParseResult<BinOp> {
-  let (text, op): (_, Vec<char>) = context("Binop", many1(one_of(OPERATOR_CHARS)))(text)?;
-  let sigil: String = op.into_iter().collect();
-  Ok((text, BinOp::from_sigil(&sigil)))
+fn operator(text: &str) -> ParseResult<Vec<char>> {
+  many1(one_of(OPERATOR_CHARS))(text)
+}
+
+fn binop(text: &str) -> ParseResult<BinOp> {
+  context("Binop", map(
+      operator,
+      |op| BinOp::from_sigil(&op.into_iter().collect::<String>())
+  ))(text)
 }
 
 fn bool_literal(text: &str) -> ParseResult<ExpressionKind> {
@@ -68,7 +73,7 @@ fn bool_literal(text: &str) -> ParseResult<ExpressionKind> {
 fn number_literal(text: &str) -> ParseResult<ExpressionKind> {
   let num_lit = many1(alt((
     map(one_of("1234567890"), |s: char| Some(s)),
-    map(nom::character::complete::char('_'), |_| None)
+    value(None, nom::character::complete::char('_')),
   )));
 
   let (text, n) = map_res(num_lit,
@@ -143,10 +148,10 @@ fn primary_expr(text: &str) -> ParseResult<ExpressionKind> {
   // primary := literal | paren_expr | if_expr | for_expr | while_expr | identifier_expr | lambda_expr | anonymous_struct | list_expr
 
   alt((
+    if_expr,
     literal,
     paren_expr,
     identifier_expr,
-    //if_expr,
   ))(text)
 }
 
@@ -160,19 +165,21 @@ fn invocation_argument(text: &str) -> ParseResult<InvocationArgument> {
   ))(text)
 }
 
-/*
 fn if_expr(text: &str) -> ParseResult<ExpressionKind> {
-  let p = preceded(tag("if"), pair(discriminator, if_expr_body));
+  let p = preceded(tag("if"), pair(ws(discriminator), ws(if_expr_body)));
   map(p, |(discriminator, body)| {
-
-  })(text)
-
-  let expr = IfExpression {
-    discriminator: Option<Box<Expression>>,
-    body: Box<IfExpressionBody>,
-  };
+    let discriminator = discriminator.map(Box::new);
+    let body = Box::new(body);
+    ExpressionKind::IfExpression { discriminator, body }
+  }) (text)
+}
+
+fn discriminator(text: &str) -> ParseResult<Option<Expression>> {
+  use nom::combinator::verify;
+  cond(text.chars().next().map(|c| c != '{').unwrap_or(true),
+    expression
+  )(text)
 }
-*/
 
 fn if_expr_body(text: &str) -> ParseResult<IfExpressionBody> {
   alt((
@@ -244,7 +251,38 @@ fn pattern_literal(text: &str) -> ParseResult<PatternLiteral> {
 }
 
 fn cond_block(text: &str) -> ParseResult<IfExpressionBody> {
-  unimplemented!()
+  use nom::character::complete::char;
+  //TODO maybe change this bit of syntax
+  let comma_or_delimitor = alt((value((), char(',')), statement_sep));
+  let p = delimited(char('{'),
+    separated_nonempty_list(comma_or_delimitor, cond_arm),
+  char('}'));
+  map(p, IfExpressionBody::CondList)(text)
+}
+
+fn cond_arm(text: &str) -> ParseResult<ConditionArm> {
+  let variant_1 = map(
+    tuple((condition, guard, tag("then"), expr_or_block)),
+    |(condition, guard, _, body)| ConditionArm { condition, guard, body }
+  );
+  let variant_2 = map(
+    preceded(tag("else"), expr_or_block),
+    |body| ConditionArm { condition: Condition::Else, guard: None, body }
+  );
+  alt((variant_1, variant_2))(text)
+}
+
+fn condition(text: &str) -> ParseResult<Condition> {
+  alt((
+    map(preceded(tag("is"), pattern), Condition::Pattern),
+    map(tuple((binop, expression)), |(op, expr)|
+      Condition::TruncatedOp(op, expr)),
+    map(expression, Condition::Expression),
+  ))(text)
+}
+
+fn guard(text: &str) -> ParseResult<Option<Expression>> {
+  opt(preceded(tag("if"), expression))(text)
 }
 
 fn expr_or_block(text: &str) -> ParseResult<Block> {
@@ -294,7 +332,7 @@ fn precedence_expr(text: &str) -> ParseResult<ExpressionKind> {
     let (mut outer_rest, mut lhs) = prefix_expr(input)?;
     loop {
       let (rest, _) = space0(outer_rest)?;
-      let (rest, maybe_binop) = opt(parse_binop)(rest)?;
+      let (rest, maybe_binop) = opt(binop)(rest)?;
       let (new_precedence, binop) = match maybe_binop {
         Some(binop) => (binop.precedence(), binop),
         None => break,