add parsing for expression blocks

src/frontend.rs

@@ -219,7 +219,7 @@ impl Context {
                         typ: self.types.primitives.infer,
                     }
                 }
-                BlockExpr::Block(_) => todo!(),
+                BlockExpr::Block(block) => todo!(),
             },
         };
         Ok(t_expr)

src/parser/block_expression.rs

@@ -2,21 +2,29 @@ use nom::{
     branch::alt,
     combinator::map,
     error::context,
-    multi::separated_list1,
-    sequence::{delimited, separated_pair, tuple},
+    multi::{many0, separated_list1},
+    sequence::{delimited, separated_pair, terminated, tuple},
 };
 
 use crate::parser::{
     expression::{expression, Expression},
-    tokens::{token, TokenKind as tk, TokenSpan},
+    tokens::{token, Token, TokenKind as tk, TokenSpan},
     IResult,
 };
 
+/// a block that is a single expression
+#[derive(Debug, Clone)]
+pub struct ExpressionBlock<'a> {
+    assignments: Vec<(Token<'a>, Expression<'a>)>,
+    value: Expression<'a>,
+}
+
+/// an expression that contains a block
 #[derive(Debug, Clone)]
 pub enum BlockExpr<'a> {
     IfElse(IfElseBlock),
     Match(MatchBlock<'a>),
-    Block(Vec<BlockExpr<'a>>),
+    Block(ExpressionBlock<'a>),
 }
 
 // TODO: postponed because annoying to implement
@@ -51,6 +59,25 @@ fn match_block(input: TokenSpan) -> IResult<TokenSpan, MatchBlock> {
     )(input)
 }
 
-pub fn block_expr(input: TokenSpan) -> IResult<TokenSpan, BlockExpr> {
-    alt((map(match_block, BlockExpr::Match),))(input)
+fn expression_block(input: TokenSpan) -> IResult<TokenSpan, ExpressionBlock> {
+    map(
+        tuple((
+            many0(tuple((
+                delimited(token(tk::Let), token(tk::Ident), token(tk::EqAssign)),
+                terminated(expression, token(tk::Semicolon)),
+            ))),
+            expression,
+        )),
+        |(assignments, value)| ExpressionBlock { assignments, value },
+    )(input)
+}
+
+pub fn block_expr(input: TokenSpan) -> IResult<TokenSpan, BlockExpr> {
+    alt((
+        map(match_block, BlockExpr::Match),
+        map(
+            delimited(token(tk::LBrace), expression_block, token(tk::RBrace)),
+            BlockExpr::Block,
+        ),
+    ))(input)
 }

src/parser/tokens.rs

@@ -86,6 +86,7 @@ pub enum TokenKind {
     State,
     Proc,
     Comb,
+    Let,
     // whitespace
     Comment,
     // Error
@@ -232,6 +233,7 @@ fn lex_keywords(input: Span) -> IResult<Span, Token> {
             map(tag("proc"), |_| TokenKind::Proc),
             map(tag("comb"), |_| TokenKind::Comb),
             map(tag("state"), |_| TokenKind::State),
+            map(tag("let"), |_| TokenKind::Let),
         ))),
         |(span, kind)| Token::new(span, kind),
     )(input)