implement . and | operators

`f . x` is the same as `f x`, and is mostly useful when used as an argument to another function call.
this allows us to simulate record field syntax very well: `d.Num` is the same as `d Num`, but with high precedence

`a |f b` is the same as `f a b` and effectively allows you to turn any function into an arithmetic operator.
it's the main reason behind + - * / having the same precedence---they now chain very nicely with pipes

closes #126 (`|` operator)
closes #127 (`.` operator)

crates/haku/src/compiler.rs

@@ -361,52 +361,43 @@ fn compile_binary<'a>(c: &mut Compiler<'a>, src: &Source<'a>, node_id: NodeId) -
     }
     let name = src.ast.span(op).slice(src.code);
 
-    if name == "=" {
-        c.emit(Diagnostic::error(
-            src.ast.span(op),
-            "defs `a = b` may only appear at the top level",
-        ));
-        return Ok(());
+    match name {
+        ":" => {
+            // Invalid use of a def inside an expression.
+            c.emit(Diagnostic::error(
+                src.ast.span(op),
+                "defs `a: b` may only appear at the top level",
+            ));
+            Ok(())
+        }
+        "." => compile_dot_call(c, src, left, right),
+        "|" => compile_pipe_call(c, src, left, right),
+        _ => {
+            compile_expr(c, src, left)?;
+            compile_expr(c, src, right)?;
+            if let Some(index) = system::resolve(SystemFnArity::Binary, name) {
+                let argument_count = 2;
+                c.chunk.emit_opcode(Opcode::System)?;
+                c.chunk.emit_u8(index)?;
+                c.chunk.emit_u8(argument_count)?;
+            } else {
+                c.emit(Diagnostic::error(
+                    src.ast.span(op),
+                    "this binary operator is currently unimplemented",
+                ));
+            }
+            Ok(())
+        }
     }
-
-    compile_expr(c, src, left)?;
-    compile_expr(c, src, right)?;
-    if let Some(index) = system::resolve(SystemFnArity::Binary, name) {
-        let argument_count = 2;
-        c.chunk.emit_opcode(Opcode::System)?;
-        c.chunk.emit_u8(index)?;
-        c.chunk.emit_u8(argument_count)?;
-    } else {
-        c.emit(Diagnostic::error(
-            src.ast.span(op),
-            "this unary operator is currently unimplemented",
-        ));
-    }
-
-    Ok(())
 }
 
-fn compile_call<'a>(c: &mut Compiler<'a>, src: &Source<'a>, node_id: NodeId) -> CompileResult {
-    let mut walk = src.ast.walk(node_id);
-    let Some(func) = walk.node() else {
-        return Ok(());
-    };
+fn emit_nary_call<'a>(
+    c: &mut Compiler<'a>,
+    src: &Source<'a>,
+    func: NodeId,
+    argument_count: u8,
+) -> CompileResult {
     let name = src.ast.span(func).slice(src.code);
-
-    let mut argument_count = 0;
-    while let Some(arg) = walk.node() {
-        compile_expr(c, src, arg)?;
-        argument_count += 1;
-    }
-
-    let argument_count = u8::try_from(argument_count).unwrap_or_else(|_| {
-        c.emit(Diagnostic::error(
-            src.ast.span(node_id),
-            "function call has too many arguments",
-        ));
-        0
-    });
-
     if let (NodeKind::Ident, Some(index)) = (
         src.ast.kind(func),
         system::resolve(SystemFnArity::Nary, name),
@@ -423,6 +414,81 @@ fn compile_call<'a>(c: &mut Compiler<'a>, src: &Source<'a>, node_id: NodeId) ->
         c.chunk.emit_opcode(Opcode::Call)?;
         c.chunk.emit_u8(argument_count)?;
     }
+    Ok(())
+}
+
+fn compile_call<'a>(c: &mut Compiler<'a>, src: &Source<'a>, node_id: NodeId) -> CompileResult {
+    let mut walk = src.ast.walk(node_id);
+    let Some(func) = walk.node() else {
+        return Ok(());
+    };
+
+    let mut argument_count = 0;
+    while let Some(arg) = walk.node() {
+        compile_expr(c, src, arg)?;
+        argument_count += 1;
+    }
+
+    let argument_count = u8::try_from(argument_count).unwrap_or_else(|_| {
+        c.emit(Diagnostic::error(
+            src.ast.span(node_id),
+            "function call has too many arguments",
+        ));
+        0
+    });
+
+    emit_nary_call(c, src, func, argument_count)?;
+
+    Ok(())
+}
+
+fn compile_dot_call<'a>(
+    c: &mut Compiler<'a>,
+    src: &Source<'a>,
+    func: NodeId,
+    right: NodeId,
+) -> CompileResult {
+    compile_expr(c, src, right)?;
+    emit_nary_call(c, src, func, 1)?;
+
+    Ok(())
+}
+
+fn compile_pipe_call<'a>(
+    c: &mut Compiler<'a>,
+    src: &Source<'a>,
+    left: NodeId,
+    call: NodeId,
+) -> CompileResult {
+    if src.ast.kind(call) != NodeKind::Call {
+        c.emit(Diagnostic::error(
+            src.ast.span(call),
+            "the right side of a pipe `|` must be a function call",
+        ));
+        return Ok(());
+    }
+
+    let mut walk = src.ast.walk(call);
+    let Some(func) = walk.node() else {
+        return Ok(());
+    };
+
+    compile_expr(c, src, left)?;
+    let mut argument_count = 1;
+    while let Some(arg) = walk.node() {
+        compile_expr(c, src, arg)?;
+        argument_count += 1;
+    }
+
+    let argument_count = u8::try_from(argument_count).unwrap_or_else(|_| {
+        c.emit(Diagnostic::error(
+            src.ast.span(call),
+            "function call has too many arguments",
+        ));
+        0
+    });
+
+    emit_nary_call(c, src, func, argument_count)?;
 
     Ok(())
 }

crates/haku/src/lexer.rs

@@ -215,6 +215,8 @@ fn token(l: &mut Lexer<'_>) -> (TokenKind, Span, bool) {
         '!' => one_or_two(l, TokenKind::Not, '=', TokenKind::NotEqual),
         '<' => one_or_two(l, TokenKind::Less, '=', TokenKind::LessEqual),
         '>' => one_or_two(l, TokenKind::Greater, '=', TokenKind::GreaterEqual),
+        '.' => one(l, TokenKind::Dot),
+        '|' => one(l, TokenKind::Pipe),
 
         '\n' => return newline(l, has_left_space),
         '(' => one(l, TokenKind::LParen),

crates/haku/src/parser.rs

@@ -327,17 +327,20 @@ fn tighter(left: (TokenKind, Spaces), right: (TokenKind, Spaces)) -> Tighter {
             | TokenKind::LessEqual
             | TokenKind::Greater
             | TokenKind::GreaterEqual => 2,
-            TokenKind::Plus | TokenKind::Minus | TokenKind::Star | TokenKind::Slash => 3,
-            // 4: reserve for `.`
+
+            TokenKind::Plus
+            | TokenKind::Minus
+            | TokenKind::Star
+            | TokenKind::Slash
+            | TokenKind::Pipe => 3,
+
+            TokenKind::Dot => 4,
             _ if is_prefix_token((kind, spaces)) => 5,
             _ => return None, // not an infix operator
         };
         Some(match kind {
-            // There are a few types of operators which are independent of tightness.
-
-            // For : and =, it does not matter if they're spelled one way or the other, because
-            // there is only one way to use them (at the beginning of the expression).
-            TokenKind::Colon | TokenKind::Equal => Tightness::Loose(index),
+            // There are a few types of operators which work independent of tightness.
+            TokenKind::Colon | TokenKind::Equal | TokenKind::Pipe => Tightness::Loose(index),
 
             // For unary -, we treat it as having Tight spacing rather than Call, else it would
             // be allowed to begin function calls.
@@ -652,7 +655,9 @@ fn infix(p: &mut Parser, op: (TokenKind, Spaces)) -> NodeKind {
         | TokenKind::LessEqual
         | TokenKind::Greater
         | TokenKind::GreaterEqual
-        | TokenKind::Colon => infix_binary(p, op),
+        | TokenKind::Colon
+        | TokenKind::Dot
+        | TokenKind::Pipe => infix_binary(p, op),
         TokenKind::Minus if spaces.are_balanced() => infix_binary(p, op),
 
         TokenKind::Equal => infix_let(p, op),

crates/haku/src/token.rs

@@ -28,6 +28,8 @@ pub enum TokenKind {
     Greater,
     GreaterEqual,
     Not,
+    Dot,
+    Pipe,
 
     // Punctuation
     Newline,