Parse function expressions

3 files changed, 127 insertions, 1 deletions

diff --git a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedExpressionNode.java b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedExpressionNode.java
index 107bc20b..e8f3842d 100644
--- a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedExpressionNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedExpressionNode.java
@@ -1,5 +1,5 @@
 package org.shedlang.compiler.ast.untyped;
 
 public sealed interface UntypedExpressionNode extends UntypedNode
-    permits UntypedBinaryOperationNode, UntypedBoolLiteralNode, UntypedCallNode, UntypedFieldAccessNode, UntypedIfNode, UntypedIntLiteralNode, UntypedReferenceNode, UntypedStringLiteralNode, UntypedTupleNode, UntypedWhenNode {
+    permits UntypedBinaryOperationNode, UntypedBoolLiteralNode, UntypedCallNode, UntypedFieldAccessNode, UntypedFunctionExpressionNode, UntypedIfNode, UntypedIntLiteralNode, UntypedReferenceNode, UntypedStringLiteralNode, UntypedTupleNode, UntypedWhenNode {
 }
diff --git a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedFunctionExpressionNode.java b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedFunctionExpressionNode.java
new file mode 100644
index 00000000..bc931a5a
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedFunctionExpressionNode.java
@@ -0,0 +1,94 @@
+package org.shedlang.compiler.ast.untyped;
+
+import org.pcollections.Empty;
+import org.pcollections.PVector;
+import org.shedlang.compiler.sources.Source;
+import org.shedlang.compiler.sources.Sources;
+
+import java.util.Optional;
+
+public record UntypedFunctionExpressionNode(
+    UntypedParamsNode params,
+    Optional<UntypedTypeLevelExpressionNode> effect,
+    UntypedTypeLevelExpressionNode returnType,
+    UntypedBlockNode body,
+    Source source
+) implements UntypedExpressionNode {
+    public static Builder builder() {
+        return new Builder(
+            Empty.vector(),
+            Empty.vector(),
+            Optional.empty(),
+            new UntypedTypeLevelReferenceNode("Unit", Sources.NULL),
+            Empty.vector()
+        );
+    }
+
+    public record Builder(
+        PVector<UntypedParamNode> positionalParams,
+        PVector<UntypedParamNode> namedParams,
+        Optional<UntypedTypeLevelExpressionNode> effect,
+        UntypedTypeLevelExpressionNode returnType,
+        PVector<UntypedFunctionStatementNode> body
+    ) {
+        public UntypedFunctionExpressionNode build() {
+            return new UntypedFunctionExpressionNode(
+                new UntypedParamsNode(positionalParams, namedParams, Sources.NULL),
+                effect,
+                returnType,
+                new UntypedBlockNode(body, Sources.NULL),
+                Sources.NULL
+            );
+        }
+
+        public Builder addPositionalParam(String name, UntypedTypeLevelExpressionNode type) {
+            return new Builder(
+                this.positionalParams.plus(new UntypedParamNode(name, type, Sources.NULL)),
+                this.namedParams,
+                this.effect,
+                this.returnType,
+                this.body
+            );
+        }
+
+        public Builder addNamedParam(String name, UntypedTypeLevelExpressionNode type) {
+            return new Builder(
+                this.positionalParams,
+                this.namedParams.plus(new UntypedParamNode(name, type, Sources.NULL)),
+                this.effect,
+                this.returnType,
+                this.body
+            );
+        }
+
+        public Builder withEffect(UntypedTypeLevelExpressionNode effect) {
+            return new Builder(
+                this.positionalParams,
+                this.namedParams,
+                Optional.of(effect),
+                this.returnType,
+                this.body
+            );
+        }
+
+        public Builder withReturnType(UntypedTypeLevelExpressionNode returnType) {
+            return new Builder(
+                this.positionalParams,
+                this.namedParams,
+                this.effect,
+                returnType,
+                this.body
+            );
+        }
+
+        public Builder addStatement(UntypedFunctionStatementNode statement) {
+            return new Builder(
+                this.positionalParams,
+                this.namedParams,
+                this.effect,
+                this.returnType,
+                this.body.plus(statement)
+            );
+        }
+    }
+}
diff --git a/src/main/java/org/shedlang/compiler/parser/Parser.java b/src/main/java/org/shedlang/compiler/parser/Parser.java
index 13b62323..fefd6d62 100644
--- a/src/main/java/org/shedlang/compiler/parser/Parser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Parser.java
@@ -314,6 +314,36 @@ public class Parser {
         );
     }
 
+    private static UntypedExpressionNode parseFunctionExpression(
+        TokenIterator<TokenType> tokens
+    ) {
+        var start = tokens.position();
+
+        tokens.skip(TokenType.KEYWORD_FN);
+
+        tokens.skip(TokenType.SYMBOL_PAREN_OPEN);
+        var params = parseParams(tokens);
+        tokens.skip(TokenType.SYMBOL_PAREN_CLOSE);
+
+        var effect = parseFunctionTypeEffect(tokens);
+
+        tokens.skip(TokenType.SYMBOL_THIN_ARROW);
+        var returnType = parseTopLevelTypeLevelExpression(tokens);
+
+        var body = parseBlock(tokens);
+
+        var end = tokens.position();
+        var source = start.to(end);
+
+        return new UntypedFunctionExpressionNode(
+            params,
+            effect,
+            returnType,
+            body,
+            source
+        );
+    }
+
     private static UntypedFunctionStatementNode parseFunctionReturn(TokenIterator<TokenType> tokens) {
         var start = tokens.position();
 
@@ -670,6 +700,8 @@ public class Parser {
 
             case KEYWORD_FALSE, KEYWORD_TRUE -> parseBoolLiteral(tokens);
 
+            case KEYWORD_FN -> parseFunctionExpression(tokens);
+
             case KEYWORD_WHEN -> parseWhen(tokens);
 
             case STRING -> parseStringLiteral(tokens);