First pass at parsing case.

src/can/mod.rs

@@ -752,7 +752,7 @@ fn canonicalize<'a>(
         | ast::Expr::QualifiedField(_, _)
         | ast::Expr::AccessorFunction(_)
         | ast::Expr::If(_)
-        | ast::Expr::Case(_)
+        | ast::Expr::Case(_, _)
         | ast::Expr::Variant(_, _)
         | ast::Expr::MalformedIdent(_)
         | ast::Expr::MalformedClosure

src/parse/ast.rs

@@ -70,7 +70,10 @@ pub enum Expr<'a> {
 
     // Conditionals
     If(&'a (Loc<Expr<'a>>, Loc<Expr<'a>>, Loc<Expr<'a>>)),
-    Case(&'a (Loc<Expr<'a>>, &'a [(Loc<Pattern<'a>>, Loc<Expr<'a>>)])),
+    Case(
+        &'a Loc<Expr<'a>>,
+        Vec<'a, &'a (Loc<Pattern<'a>>, Loc<Expr<'a>>)>,
+    ),
 
     // Blank Space (e.g. comments, spaces, newlines) before or after an expression.
     // We preserve this for the formatter; canonicalization ignores it.
@@ -310,7 +313,6 @@ fn pattern_size() {
 /// "currently attempting to parse a list." This helps error messages!
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Attempting {
-    Expression,
     List,
     Keyword,
     StringLiteral,
@@ -325,6 +327,8 @@ pub enum Attempting {
     Module,
     Record,
     Identifier,
+    CaseCondition,
+    CaseBranch,
 }
 
 impl<'a> Expr<'a> {

src/parse/mod.rs

@@ -24,6 +24,7 @@ use bumpalo::collections::String;
 use bumpalo::collections::Vec;
 use bumpalo::Bump;
 use operator::Operator;
+use parse;
 use parse::ast::{Attempting, Def, Expr, Pattern, Spaceable};
 use parse::blankspace::{
     space0, space0_after, space0_around, space0_before, space1, space1_around, space1_before,
@@ -32,11 +33,10 @@ use parse::ident::{ident, Ident, MaybeQualified};
 use parse::number_literal::number_literal;
 use parse::parser::{
     and, attempt, between, char, either, loc, map, map_with_arena, not, not_followed_by, one_of16,
-    one_of2, one_of4, one_of5, one_of9, one_or_more, optional, sep_by0, skip_first, skip_second,
-    string, then, unexpected, unexpected_eof, zero_or_more, Either, Fail, FailReason, ParseResult,
-    Parser, State,
+    one_of2, one_of5, one_of9, one_or_more, optional, sep_by0, skip_first, skip_second, string,
+    then, unexpected, unexpected_eof, zero_or_more, Either, Fail, FailReason, ParseResult, Parser,
+    State,
 };
-use parse::string_literal::string_literal;
 use region::Located;
 
 // pub fn api<'a>() -> impl Parser<'a, Module<'a>> {
@@ -121,7 +121,7 @@ fn parse_expr<'a>(min_indent: u16, arena: &'a Bump, state: State<'a>) -> ParseRe
         },
     );
 
-    attempt(Attempting::Expression, expr_parser).parse(arena, state)
+    expr_parser.parse(arena, state)
 }
 
 pub fn loc_parenthetical_expr<'a>(min_indent: u16) -> impl Parser<'a, Located<Expr<'a>>> {
@@ -290,7 +290,7 @@ fn expr_to_pattern<'a>(arena: &'a Bump, expr: &Expr<'a>) -> Result<Pattern<'a>,
         | Expr::AssignField(_, _)
         | Expr::Defs(_)
         | Expr::If(_)
-        | Expr::Case(_)
+        | Expr::Case(_, _)
         | Expr::MalformedClosure
         | Expr::QualifiedField(_, _) => Err(Fail {
             attempting: Attempting::Def,
@@ -543,14 +543,19 @@ fn parse_closure_param<'a>(
 }
 
 fn pattern<'a>(min_indent: u16) -> impl Parser<'a, Pattern<'a>> {
-    one_of4(
+    one_of5(
         underscore_pattern(),
         variant_pattern(),
         ident_pattern(),
         record_destructure(min_indent),
+        string_pattern(),
     )
 }
 
+fn string_pattern<'a>() -> impl Parser<'a, Pattern<'a>> {
+    map(parse::string_literal::parse(), Pattern::StrLiteral)
+}
+
 fn underscore_pattern<'a>() -> impl Parser<'a, Pattern<'a>> {
     map(char('_'), |_| Pattern::Underscore)
 }
@@ -576,10 +581,115 @@ fn ident_pattern<'a>() -> impl Parser<'a, Pattern<'a>> {
     map(unqualified_ident(), Pattern::Identifier)
 }
 
-pub fn case_expr<'a>(_min_indent: u16) -> impl Parser<'a, Expr<'a>> {
-    map(string(keyword::CASE), |_| {
-        panic!("TODO implement WHEN");
-    })
+pub fn case_expr<'a>(min_indent: u16) -> impl Parser<'a, Expr<'a>> {
+    then(
+        and(
+            case_with_indent(),
+            attempt(
+                Attempting::CaseCondition,
+                skip_second(
+                    space1_around(
+                        loc(move |arena, state| parse_expr(min_indent, arena, state)),
+                        min_indent,
+                    ),
+                    string(keyword::WHEN),
+                ),
+            ),
+        ),
+        move |arena, state, (case_indent, loc_condition)| {
+            if case_indent < min_indent {
+                panic!("TODO case wasns't indented enough");
+            }
+
+            // Everything in the branches must be indented at least as much as the case itself.
+            let min_indent = case_indent;
+
+            let (branches, state) =
+                attempt(Attempting::CaseBranch, case_branches(min_indent)).parse(arena, state)?;
+
+            Ok((Expr::Case(arena.alloc(loc_condition), branches), state))
+        },
+    )
+}
+
+pub fn case_branches<'a>(
+    min_indent: u16,
+) -> impl Parser<'a, Vec<'a, &'a (Located<Pattern<'a>>, Located<Expr<'a>>)>> {
+    move |arena, state| {
+        let mut branches: Vec<'a, &'a (Located<Pattern<'a>>, Located<Expr<'a>>)> =
+            Vec::with_capacity_in(2, arena);
+
+        // 1. Parse the first branch and get its indentation level. (It must be >= min_indent.)
+        // 2. Parse the other branches. Their indentation levels must be == the first branch's.
+
+        let (mut loc_first_pattern, state) =
+            space1_before(loc(pattern(min_indent)), min_indent).parse(arena, state)?;
+        let original_indent = state.indent_col;
+        let indented_more = original_indent + 1;
+        let (spaces_before_arrow, state) = space0(min_indent).parse(arena, state)?;
+
+        // Record the spaces before the first "->", if any.
+        if !spaces_before_arrow.is_empty() {
+            let region = loc_first_pattern.region;
+            let value =
+                Pattern::SpaceAfter(arena.alloc(loc_first_pattern.value), spaces_before_arrow);
+
+            loc_first_pattern = Located { region, value };
+        };
+
+        // Parse the first "->" and the expression after it.
+        let (loc_first_expr, mut state) = skip_first(
+            string("->"),
+            // The expr must be indented more than the pattern preceding it
+            space0_before(
+                loc(move |arena, state| parse_expr(indented_more, arena, state)),
+                indented_more,
+            ),
+        )
+        .parse(arena, state)?;
+
+        // Record this as the first branch, then optionally parse additional branches.
+        branches.push(arena.alloc((loc_first_pattern, loc_first_expr)));
+
+        let branch_parser = and(
+            then(
+                space1_around(loc(pattern(min_indent)), min_indent),
+                move |_arena, state, loc_pattern| {
+                    if state.indent_col == original_indent {
+                        Ok((loc_pattern, state))
+                    } else {
+                        panic!(
+                            "TODO additional branch didn't have same indentation as first branch"
+                        );
+                    }
+                },
+            ),
+            skip_first(
+                string("->"),
+                space1_before(
+                    loc(move |arena, state| parse_expr(min_indent, arena, state)),
+                    min_indent,
+                ),
+            ),
+        );
+
+        loop {
+            match branch_parser.parse(arena, state) {
+                Ok((next_output, next_state)) => {
+                    state = next_state;
+
+                    branches.push(arena.alloc(next_output));
+                }
+                Err((_, old_state)) => {
+                    state = old_state;
+
+                    break;
+                }
+            }
+        }
+
+        Ok((branches, state))
+    }
 }
 
 pub fn if_expr<'a>(min_indent: u16) -> impl Parser<'a, Expr<'a>> {
@@ -716,6 +826,14 @@ pub fn equals_with_indent<'a>() -> impl Parser<'a, u16> {
     }
 }
 
+pub fn case_with_indent<'a>() -> impl Parser<'a, u16> {
+    move |arena, state: State<'a>| {
+        string(keyword::CASE)
+            .parse(arena, state)
+            .map(|((), state)| ((state.indent_col, state)))
+    }
+}
+
 fn ident_to_expr<'a>(src: Ident<'a>) -> Expr<'a> {
     match src {
         Ident::Var(info) => Expr::Var(info.module_parts, info.value),
@@ -860,6 +978,10 @@ fn unqualified_ident<'a>() -> impl Parser<'a, &'a str> {
     variant_or_ident(|first_char| first_char.is_lowercase())
 }
 
+pub fn string_literal<'a>() -> impl Parser<'a, Expr<'a>> {
+    map(parse::string_literal::parse(), Expr::Str)
+}
+
 fn variant_or_ident<'a, F>(pred: F) -> impl Parser<'a, &'a str>
 where
     F: Fn(char) -> bool,

src/parse/string_literal.rs

@@ -1,9 +1,9 @@
 use bumpalo::Bump;
-use parse::ast::{Attempting, Expr};
+use parse::ast::Attempting;
 use parse::parser::{unexpected, unexpected_eof, ParseResult, Parser, State};
 use std::char;
 
-pub fn string_literal<'a>() -> impl Parser<'a, Expr<'a>> {
+pub fn parse<'a>() -> impl Parser<'a, &'a str> {
     move |arena: &'a Bump, state: State<'a>| {
         let mut chars = state.input.chars();
 
@@ -36,23 +36,23 @@ pub fn string_literal<'a>() -> impl Parser<'a, Expr<'a>> {
 
             // Potentially end the string (unless this is an escaped `"`!)
             if ch == '"' && prev_ch != '\\' {
-                let expr = if parsed_chars == 2 {
+                let string = if parsed_chars == 2 {
                     if let Some('"') = chars.next() {
                         // If the first three chars were all `"`, then this
                         // literal begins with `"""` and is a block string.
                         return parse_block_string(arena, state, &mut chars);
                     } else {
-                        Expr::Str("")
+                        ""
                     }
                 } else {
                     // Start at 1 so we omit the opening `"`.
                     // Subtract 1 from parsed_chars so we omit the closing `"`.
-                    Expr::Str(&state.input[1..(parsed_chars - 1)])
+                    &state.input[1..(parsed_chars - 1)]
                 };
 
                 let next_state = state.advance_without_indenting(parsed_chars)?;
 
-                return Ok((expr, next_state));
+                return Ok((string, next_state));
             } else if ch == '\n' {
                 // This is a single-line string, which cannot have newlines!
                 // Treat this as an unclosed string literal, and consume
@@ -83,7 +83,7 @@ fn parse_block_string<'a, I>(
     _arena: &'a Bump,
     _state: State<'a>,
     _chars: &mut I,
-) -> ParseResult<'a, Expr<'a>>
+) -> ParseResult<'a, &'a str>
 where
     I: Iterator<Item = char>,
 {

tests/helpers/mod.rs

@@ -13,17 +13,14 @@ use roc::ident::Ident;
 use roc::parse;
 use roc::parse::ast::{self, Attempting};
 use roc::parse::blankspace::space0_before;
-use roc::parse::parser::{attempt, loc, map, Fail, Parser, State};
+use roc::parse::parser::{loc, map, Fail, Parser, State};
 use roc::region::{Located, Region};
 
 pub fn parse_with<'a>(arena: &'a Bump, input: &'a str) -> Result<ast::Expr<'a>, Fail> {
     let state = State::new(&input, Attempting::Module);
-    let parser = attempt(
-        Attempting::Expression,
-        map(space0_before(loc(parse::expr(0)), 0), |loc_expr| {
-            loc_expr.value
-        }),
-    );
+    let parser = map(space0_before(loc(parse::expr(0)), 0), |loc_expr| {
+        loc_expr.value
+    });
     let answer = parser.parse(&arena, state);
 
     answer.map(|(expr, _)| expr).map_err(|(fail, _)| fail)

tests/test_parse.rs

@@ -111,7 +111,7 @@ mod test_parse {
 
     #[test]
     fn empty_source_file() {
-        assert_parsing_fails("", FailReason::Eof(Region::zero()), Attempting::Expression);
+        assert_parsing_fails("", FailReason::Eof(Region::zero()), Attempting::Module);
     }
 
     #[test]
@@ -131,7 +131,7 @@ mod test_parse {
         assert_parsing_fails(
             &too_long_str,
             FailReason::LineTooLong(0),
-            Attempting::Expression,
+            Attempting::Module,
         );
     }
 
@@ -818,6 +818,32 @@ mod test_parse {
         );
     }
 
+    // CASE
+
+    // #[test]
+    // fn two_branch_case() {
+    //     let arena = Bump::new();
+    //     let module_parts = Vec::new_in(&arena).into_bump_slice();
+    //     let arg1 = Located::new(0, 0, 2, 3, Var(module_parts, "b"));
+    //     let arg2 = Located::new(0, 0, 4, 5, Var(module_parts, "c"));
+    //     let arg3 = Located::new(0, 0, 6, 7, Var(module_parts, "d"));
+    //     let args = bumpalo::vec![in &arena; arg1, arg2, arg3];
+    //     let tuple = arena.alloc((Located::new(0, 0, 0, 1, Var(module_parts, "a")), args));
+    //     let expected = Expr::Apply(tuple);
+    //     let actual = parse_with(
+    //         &arena,
+    //         indoc!(
+    //             r#"
+    //             case foo bar baz when
+    //              "blah" -> foo a b
+    //              "mise" -> bar c d
+    //             "#
+    //         ),
+    //     );
+
+    //     assert_eq!(Ok(expected), actual);
+    // }
+
     // TODO test hex/oct/binary parsing
     //
     // TODO test for \t \r and \n in string literals *outside* unicode escape sequence!