Parse function expressions

10 files changed, 337 insertions, 1 deletions

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();
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNodeMatcher.java b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNodeMatcher.java
new file mode 100644
index 0000000..71356e8
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedFunctionExpressionNodeMatcher.java
@@ -0,0 +1,53 @@
+// Generated by hobgoblin.
+
+package org.zwobble.hobgoblin.compiler.ast.untyped;
+
+// Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher imports
+// Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher imports
+
+public final class UntypedFunctionExpressionNodeMatcher implements org.zwobble.precisely.Matcher<java.lang.Object> {
+    public static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher isUntypedFunctionExpressionNode() {
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher(java.util.List.of());
+    }
+
+    private final java.util.List<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode>> submatchers;
+
+    private UntypedFunctionExpressionNodeMatcher(
+        java.util.List<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode>> submatchers
+    ) {
+        this.submatchers = submatchers;
+    }
+
+    public org.zwobble.precisely.MatchResult match(java.lang.Object actual) {
+        return this.toMatcher().match(actual);
+    }
+
+    public org.zwobble.precisely.TextTree describe() {
+        return this.toMatcher().describe();
+    }
+
+    private org.zwobble.precisely.Matcher<java.lang.Object> toMatcher() {
+        return org.zwobble.precisely.Matchers.instanceOf(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode.class, this.submatchers);
+    }
+
+    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher withParams(org.zwobble.precisely.Matcher<? super java.util.List<org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>> params) {
+        var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode>>(this.submatchers);
+        submatchers.add(org.zwobble.precisely.Matchers.has("params", org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode::params, (org.zwobble.precisely.Matcher) params));
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher(submatchers);
+    }
+
+    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher withBody(org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedExpressionNode> body) {
+        var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode>>(this.submatchers);
+        submatchers.add(org.zwobble.precisely.Matchers.has("body", org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode::body, (org.zwobble.precisely.Matcher) body));
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher(submatchers);
+    }
+
+    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher withSource(org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.sources.Source> source) {
+        var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode>>(this.submatchers);
+        submatchers.add(org.zwobble.precisely.Matchers.has("source", org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNode::source, (org.zwobble.precisely.Matcher) source));
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher(submatchers);
+    }
+
+    // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher body
+    // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher body
+}
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNodeMatcher.java b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNodeMatcher.java
new file mode 100644
index 0000000..c140fb2
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/ast/untyped/UntypedParamNodeMatcher.java
@@ -0,0 +1,47 @@
+// Generated by hobgoblin.
+
+package org.zwobble.hobgoblin.compiler.ast.untyped;
+
+// Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher imports
+// Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher imports
+
+public final class UntypedParamNodeMatcher implements org.zwobble.precisely.Matcher<java.lang.Object> {
+    public static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher isUntypedParamNode() {
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher(java.util.List.of());
+    }
+
+    private final java.util.List<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>> submatchers;
+
+    private UntypedParamNodeMatcher(
+        java.util.List<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>> submatchers
+    ) {
+        this.submatchers = submatchers;
+    }
+
+    public org.zwobble.precisely.MatchResult match(java.lang.Object actual) {
+        return this.toMatcher().match(actual);
+    }
+
+    public org.zwobble.precisely.TextTree describe() {
+        return this.toMatcher().describe();
+    }
+
+    private org.zwobble.precisely.Matcher<java.lang.Object> toMatcher() {
+        return org.zwobble.precisely.Matchers.instanceOf(org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode.class, this.submatchers);
+    }
+
+    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher withName(org.zwobble.precisely.Matcher<? super String> name) {
+        var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>>(this.submatchers);
+        submatchers.add(org.zwobble.precisely.Matchers.has("name", org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode::name, (org.zwobble.precisely.Matcher) name));
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher(submatchers);
+    }
+
+    public org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher withSource(org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.sources.Source> source) {
+        var submatchers = new java.util.ArrayList<org.zwobble.precisely.Matcher<? super org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode>>(this.submatchers);
+        submatchers.add(org.zwobble.precisely.Matchers.has("source", org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNode::source, (org.zwobble.precisely.Matcher) source));
+        return new org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher(submatchers);
+    }
+
+    // Custom area start: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher body
+    // Custom area end: org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher body
+}
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserFunctionExpressionTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserFunctionExpressionTests.java
new file mode 100644
index 0000000..99cf3c0
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserFunctionExpressionTests.java
@@ -0,0 +1,55 @@
+package org.zwobble.hobgoblin.compiler.parser;
+
+import org.junit.jupiter.api.Test;
+
+import static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedFunctionExpressionNodeMatcher.isUntypedFunctionExpressionNode;
+import static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedParamNodeMatcher.isUntypedParamNode;
+import static org.zwobble.hobgoblin.compiler.ast.untyped.UntypedReferenceNodeMatcher.isUntypedReferenceNode;
+import static org.zwobble.hobgoblin.compiler.parser.ParserTesting.parseString;
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.equalTo;
+import static org.zwobble.precisely.Matchers.isSequence;
+
+public class ParserFunctionExpressionTests {
+    @Test
+    public void canParseFunctionExpressionWithNoParams() {
+        var source = "$() => x";
+
+        var node = parseString(source, Parser::parseTopLevelExpression);
+
+        assertThat(node, isUntypedFunctionExpressionNode()
+            .withParams(isSequence())
+            .withBody(isUntypedReferenceNode().withName(equalTo("x")))
+        );
+    }
+
+    @Test
+    public void canParseFunctionExpressionWithOneParam() {
+        var source = "$(a) => x";
+
+        var node = parseString(source, Parser::parseTopLevelExpression);
+
+        assertThat(node, isUntypedFunctionExpressionNode()
+            .withParams(isSequence(
+                isUntypedParamNode().withName(equalTo("a"))
+            ))
+            .withBody(isUntypedReferenceNode().withName(equalTo("x")))
+        );
+    }
+    @Test
+    public void canParseFunctionExpressionWithMultipleParams() {
+        var source = "$(a, b, c) => x";
+
+        var node = parseString(source, Parser::parseTopLevelExpression);
+
+        assertThat(node, isUntypedFunctionExpressionNode()
+            .withParams(isSequence(
+                isUntypedParamNode().withName(equalTo("a")),
+                isUntypedParamNode().withName(equalTo("b")),
+                isUntypedParamNode().withName(equalTo("c"))
+            ))
+            .withBody(isUntypedReferenceNode().withName(equalTo("x")))
+        );
+    }
+}
+
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/parser/TokenizerTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/parser/TokenizerTests.java
index 39aded5..d5b7347 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/parser/TokenizerTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/parser/TokenizerTests.java
@@ -173,6 +173,17 @@ public class TokenizerTests {
     }
 
     @Test
+    public void symbolDollarIsTokenized() {
+        var sourceText = SourceText.fromString("<string>", "$");
+
+        var tokens = Tokenizer.tokenize(sourceText);
+
+        assertThat(tokens.tokens(), isSequence(
+            equalTo(new Token(TokenType.SYMBOL_DOLLAR, sourceRange(sourceText, 0, 1)))
+        ));
+    }
+
+    @Test
     public void symbolDotIsTokenized() {
         var sourceText = SourceText.fromString("<string>", ".");
 
@@ -195,6 +206,17 @@ public class TokenizerTests {
     }
 
     @Test
+    public void symbolFatArrowIsTokenized() {
+        var sourceText = SourceText.fromString("<string>", "=>");
+
+        var tokens = Tokenizer.tokenize(sourceText);
+
+        assertThat(tokens.tokens(), isSequence(
+            equalTo(new Token(TokenType.SYMBOL_FAT_ARROW, sourceRange(sourceText, 0, 2)))
+        ));
+    }
+
+    @Test
     public void symbolForwardSlashIsTokenized() {
         var sourceText = SourceText.fromString("<string>", "/");