From 6d211928a40953bbebbee574fa5e8928a3ea687b Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 25 Oct 2026 10:11:50 +0000
Subject: Parse function expressions

---
 .../ast/untyped/UntypedExpressionNode.java         |  2 +-
 .../ast/untyped/UntypedFunctionExpressionNode.java | 60 ++++++++++++++++++++++
 .../compiler/ast/untyped/UntypedParamNode.java     | 38 ++++++++++++++
 .../zwobble/hobgoblin/compiler/parser/Parser.java  | 50 ++++++++++++++++++
 .../hobgoblin/compiler/parser/TokenType.java       |  2 +
 .../hobgoblin/compiler/parser/Tokenizer.java       |  9 ++++
 6 files changed, 160 insertions(+), 1 deletion(-)
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNode.java
 create mode 100644 src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNode.java

(limited to 'src/main/java')

diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedExpressionNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedExpressionNode.java
index 11f6b67..a5c54a0 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedExpressionNode.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedExpressionNode.java
@@ -5,7 +5,7 @@ package org.zwobble.hobgoblin.compiler.ast.untyped;
 // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode imports
 // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode imports
 
-public sealed interface UntypedExpressionNode permits org.zwobble.hobgoblin.compiler.ast.untyped.UntypedCallNode, org.zwobble.hobgoblin.compiler.ast.untyped.UntypedMemberAccessNode, org.zwobble.hobgoblin.compiler.ast.untyped.UntypedReferenceNode {
+public sealed interface UntypedExpressionNode permits org.zwobble.hobgoblin.compiler.ast.untyped.UntypedCallNode, org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode, org.zwobble.hobgoblin.compiler.ast.untyped.UntypedMemberAccessNode, org.zwobble.hobgoblin.compiler.ast.untyped.UntypedReferenceNode {
     public interface Builder {
         public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode build();
 
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNode.java
new file mode 100644
index 0000000..4e410f3
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNode.java
@@ -0,0 +1,60 @@
+// Generated by hobgoblin.
+
+package org.zwobble.hobgoblin.compiler.ast.untyped;
+
+// Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode imports
+// Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode imports
+
+public record UntypedFunctionExpressionNode(
+    java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode> params,
+    org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode body,
+    org.zwobble.hobgoblin.compiler.sources.Source source
+) implements org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode {
+    public static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder arbitrary() {
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(java.util.List.of(), org.zwobble.hobgoblin.compiler.ast.untyped.UntypedReferenceNode.arbitrary().build(), org.zwobble.hobgoblin.compiler.sources.HobgoblinNativeSources.arbitrarySource());
+    }
+
+    public record Builder(
+        java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode> params,
+        org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode body,
+        org.zwobble.hobgoblin.compiler.sources.Source source
+    ) implements org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode.Builder {
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode build() {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode(params, body, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder withParams(java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode> params) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(params, body, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder addParam(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode param) {
+            var params = new java.util.ArrayList<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>(this.params);
+            params.add(param);
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(params, body, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder addParam(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder param) {
+            var params = new java.util.ArrayList<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>(this.params);
+            params.add(param.build());
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(params, body, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder withBody(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode body) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(params, body, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder withBody(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode.Builder body) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(params, body.build(), source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder withSource(org.zwobble.hobgoblin.compiler.sources.Source source) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder(params, body, source);
+        }
+
+        // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder body
+        // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.Builder body
+    }
+
+    // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode body
+    // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode body
+}
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNode.java b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNode.java
new file mode 100644
index 0000000..068097f
--- /dev/null
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNode.java
@@ -0,0 +1,38 @@
+// Generated by hobgoblin.
+
+package org.zwobble.hobgoblin.compiler.ast.untyped;
+
+// Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode imports
+// Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode imports
+
+public record UntypedParamNode(
+    String name,
+    org.zwobble.hobgoblin.compiler.sources.Source source
+) {
+    public static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder arbitrary() {
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder("", org.zwobble.hobgoblin.compiler.sources.HobgoblinNativeSources.arbitrarySource());
+    }
+
+    public record Builder(
+        String name,
+        org.zwobble.hobgoblin.compiler.sources.Source source
+    ) {
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode build() {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode(name, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder withName(String name) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder(name, source);
+        }
+
+        public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder withSource(org.zwobble.hobgoblin.compiler.sources.Source source) {
+            return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder(name, source);
+        }
+
+        // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder body
+        // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.Builder body
+    }
+
+    // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode body
+    // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode body
+}
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
index 976ab75..cdeeedd 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
@@ -457,6 +457,19 @@ public class Parser {
         return Optional.of(typeParams);
     }
 
+    // == Params ==
+
+    private static UntypedParamNode parseParam(TokenIterator tokens) {
+        var start = tokens.startPosition();
+
+        var name = parseIdentifier(tokens);
+
+        var end = tokens.endPosition();
+        var source = createSource(start, end);
+
+        return new UntypedParamNode(name, source);
+    }
+
     // == Type-level expressions ==
 
     static UntypedTypeLevelExpressionNode parseTypeLevelExpression(
@@ -545,6 +558,43 @@ public class Parser {
     private static UntypedExpressionNode parsePrimaryExpression(
         TokenIterator tokens
     ) {
+        if (tokens.isNext(TokenType.SYMBOL_DOLLAR)) {
+            return parseFunctionExpression(tokens);
+        } else if (tokens.isNext(TokenType.IDENTIFIER)) {
+            return parseReference(tokens);
+        } else {
+            throw new UnsupportedOperationException("TODO");
+        }
+    }
+
+    private static UntypedFunctionExpressionNode parseFunctionExpression(TokenIterator tokens) {
+        var start = tokens.startPosition();
+
+        tokens.skip(TokenType.SYMBOL_DOLLAR);
+        tokens.skip(TokenType.SYMBOL_PAREN_OPEN);
+
+        var params = parseMany(
+            () -> tokens.isNext(TokenType.SYMBOL_PAREN_CLOSE),
+            () -> parseParam(tokens),
+            () -> tokens.trySkip(TokenType.SYMBOL_COMMA)
+        );
+
+        tokens.skip(TokenType.SYMBOL_PAREN_CLOSE);
+        tokens.skip(TokenType.SYMBOL_FAT_ARROW);
+
+        var body = parseTopLevelExpression(tokens);
+
+        var end = tokens.endPosition();
+        var source = createSource(start, end);
+
+        return new UntypedFunctionExpressionNode(
+            params,
+            body,
+            source
+        );
+    }
+
+    private static UntypedReferenceNode parseReference(TokenIterator tokens) {
         var start = tokens.startPosition();
 
         var name = parseIdentifier(tokens);
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenType.java b/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenType.java
index 2a85072..1181fca 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenType.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/parser/TokenType.java
@@ -19,8 +19,10 @@ enum TokenType {
     SYMBOL_BRACE_CLOSE,
     SYMBOL_COLON,
     SYMBOL_COMMA,
+    SYMBOL_DOLLAR,
     SYMBOL_DOT,
     SYMBOL_DOT_DOT,
+    SYMBOL_FAT_ARROW,
     SYMBOL_FORWARD_SLASH,
     SYMBOL_PAREN_OPEN,
     SYMBOL_PAREN_CLOSE,
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Tokenizer.java b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Tokenizer.java
index 1a775b0..56c2123 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Tokenizer.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Tokenizer.java
@@ -154,6 +154,10 @@ class Tokenizer {
             tokenType = TokenType.SYMBOL_DOT_DOT;
             iterator.skip();
             iterator.skip();
+        } else if ("=>".contentEquals(iterator.peekSequence(2))) {
+            tokenType = TokenType.SYMBOL_FAT_ARROW;
+            iterator.skip();
+            iterator.skip();
         } else {
             switch (iterator.peek()) {
                 case '{':
@@ -176,6 +180,11 @@ class Tokenizer {
                     iterator.skip();
                     break;
 
+                case '$':
+                    tokenType = TokenType.SYMBOL_DOLLAR;
+                    iterator.skip();
+                    break;
+
                 case '.':
                     tokenType = TokenType.SYMBOL_DOT;
                     iterator.skip();
-- 
cgit v1.2.3