parse function application

README.md

@@ -73,3 +73,23 @@ compose f g x == (((compose f) g) x) == compose {f: f2, g} x == compose {x} f g
 ```rust
 fn id([x]) ()
 ```
+
+"Maps" should really just be blocks
+```rust
+foo := 3;
+{ 
+   x := 42;
+   ^twice_x := x * 2;
+   ^thrice_x := x * 3;
+   ^foo;
+}
+```
+becomes
+```json5
+{
+    "twice_x": 84,
+    "thrice_x": 126,
+    // ^foo as a statement behaves like ^foo := foo, so we get that nice record field punning
+    "foo": 3,
+}
+```

src/parser.rs

@@ -17,6 +17,9 @@ enum Token<'a> {
     #[token(":")]
     Colon,
 
+    #[token(",")]
+    Comma,
+
     #[token(";")]
     Semicolon,
 
@@ -44,9 +47,6 @@ enum Token<'a> {
     #[regex(r"[+*/%=-]")]
     BinOp(&'a str),
 
-    #[token("fn")]
-    Fn,
-
     #[regex(r"[a-zA-Z_][a-zA-Z_0-9']*")]
     Var(&'a str),
 
@@ -60,6 +60,7 @@ impl fmt::Display for Token<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Token::Colon => write!(f, ":"),
+            Token::Comma => write!(f, ","),
             Token::Semicolon => write!(f, ";"),
             Token::Set => write!(f, ":="),
             Token::OpenParen => write!(f, "("),
@@ -69,7 +70,6 @@ impl fmt::Display for Token<'_> {
             Token::OpenBrace => write!(f, "{{"),
             Token::CloseBrace => write!(f, "}}"),
             Token::Return => write!(f, "^"),
-            Token::Fn => write!(f, "fn"),
             Token::BinOp(x) | Token::Var(x) | Token::Num(x) => write!(f, "{x}"),
             Token::Error => write!(f, "ERROR"),
         }
@@ -85,14 +85,24 @@ fn parser<'tokens, 'src: 'tokens, I>()
 where
     I: ValueInput<'tokens, Token = Token<'src>, Span = SimpleSpan>,
 {
+    let semicolon = just(Token::Semicolon)
+        .repeated()
+        .at_least(1)
+        .labelled("semicolon");
+
     recursive(|expr| {
+        let expr = expr.labelled("expression");
+
         let ident = choice((
-            just(Token::Return).ignore_then(select! {
+            just(Token::Return)
+                .ignore_then(select! {
                     Token::Var(s) => Ident::Return(s.to_owned())
-            }),
+                })
+                .labelled("return identifier"),
             select! {
                 Token::Var(s) => Ident::Local(s.to_owned()),
-            },
+            }
+            .labelled("local identifier"),
         ))
         .labelled("identifier");
 
@@ -115,22 +125,28 @@ where
         })
         .labelled("number");
 
-        let semicolon = just(Token::Semicolon)
+        let block = expr
-            .repeated()
+            .clone()
-            .at_least(1)
+            .separated_by(semicolon.clone())
-            .labelled("semicolon");
+            .collect()
-
-        let block = just(Token::OpenParen)
-            .ignore_then(expr.clone().separated_by(semicolon).collect())
-            .then_ignore(just(Token::CloseParen))
             .map(Ast::Block)
+            .delimited_by(just(Token::OpenParen), just(Token::CloseParen))
             .labelled("block");
 
-        choice((set, ident.map(Ast::Var).labelled("variable"), num, block))
+        let non_app = choice((set, num, ident.map(Ast::Var).labelled("variable"), block));
+
+        let app = non_app
+            .clone()
+            .foldl(non_app.clone().repeated(), |f, x| {
+                Ast::App(Box::new(f), Box::new(x))
+            })
+            .labelled("function application");
+
+        app.or(non_app)
     })
     .labelled("expression")
-    .then_ignore(just(Token::Semicolon).repeated().at_least(1))
+    .separated_by(semicolon)
-    .repeated()
+    .allow_trailing()
     .collect()
 }