Parse when expressions

7 files changed, 70 insertions, 2 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 b1d7ba83..107bc20b 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 {
+    permits UntypedBinaryOperationNode, UntypedBoolLiteralNode, UntypedCallNode, UntypedFieldAccessNode, UntypedIfNode, UntypedIntLiteralNode, UntypedReferenceNode, UntypedStringLiteralNode, UntypedTupleNode, UntypedWhenNode {
 }
diff --git a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedWhenCaseNode.java b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedWhenCaseNode.java
new file mode 100644
index 00000000..7b3e95b9
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedWhenCaseNode.java
@@ -0,0 +1,10 @@
+package org.shedlang.compiler.ast.untyped;
+
+import org.shedlang.compiler.sources.Source;
+
+public record UntypedWhenCaseNode(
+    UntypedTypeLevelExpressionNode caseType,
+    UntypedBlockNode body,
+    Source source
+) implements UntypedNode {
+}
diff --git a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedWhenNode.java b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedWhenNode.java
new file mode 100644
index 00000000..e8c2d348
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedWhenNode.java
@@ -0,0 +1,12 @@
+package org.shedlang.compiler.ast.untyped;
+
+import org.shedlang.compiler.sources.Source;
+
+import java.util.List;
+
+public record UntypedWhenNode(
+    UntypedExpressionNode expression,
+    List<UntypedWhenCaseNode> cases,
+    Source source
+) implements UntypedExpressionNode {
+}
diff --git a/src/main/java/org/shedlang/compiler/parser/Parser.java b/src/main/java/org/shedlang/compiler/parser/Parser.java
index 84900688..71490933 100644
--- a/src/main/java/org/shedlang/compiler/parser/Parser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Parser.java
@@ -540,6 +540,8 @@ public class Parser {
             case KEYWORD_IF -> parseIf(tokens);
 
             case KEYWORD_FALSE, KEYWORD_TRUE -> parseBoolLiteral(tokens);
+            
+            case KEYWORD_WHEN -> parseWhen(tokens);
 
             case STRING -> parseStringLiteral(tokens);
 
@@ -812,7 +814,6 @@ public class Parser {
         return new UntypedTupleTypeNode(elements, source);
     }
 
-
     private static UntypedTypeLevelReferenceNode parseTypeLevelReference(TokenIterator<TokenType> tokens) {
         var start = tokens.position();
 
@@ -824,6 +825,44 @@ public class Parser {
         return new UntypedTypeLevelReferenceNode(name, source);
     }
 
+    private static UntypedExpressionNode parseWhen(TokenIterator<TokenType> tokens) {
+        var start = tokens.position();
+
+        tokens.skip(TokenType.KEYWORD_WHEN);
+
+        tokens.skip(TokenType.SYMBOL_PAREN_OPEN);
+        var expression = parseTopLevelExpression(tokens);
+        tokens.skip(TokenType.SYMBOL_PAREN_CLOSE);
+
+        tokens.skip(TokenType.SYMBOL_BRACE_OPEN);
+        var cases = parseMany(
+            () -> tokens.isNext(TokenType.SYMBOL_BRACE_CLOSE),
+            () -> parseWhenCase(tokens),
+            () -> true
+        );
+        tokens.skip(TokenType.SYMBOL_BRACE_CLOSE);
+
+        var end = tokens.position();
+        var source = start.to(end);
+
+        return new UntypedWhenNode(expression, cases, source);
+    }
+
+    private static UntypedWhenCaseNode parseWhenCase(TokenIterator<TokenType> tokens) {
+        var start = tokens.position();
+
+        tokens.skip(TokenType.KEYWORD_IS);
+
+        var caseType = parseTopLevelTypeLevelExpression(tokens);
+
+        var body = parseBlock(tokens);
+
+        var end = tokens.position();
+        var source = start.to(end);
+
+        return new UntypedWhenCaseNode(caseType, body, source);
+    }
+
     private static UntypedFunctionStatementNode parseWhile(
         TokenIterator<TokenType> tokens
     ) {
diff --git a/src/main/java/org/shedlang/compiler/parser/TokenType.java b/src/main/java/org/shedlang/compiler/parser/TokenType.java
index 9c8183dc..e2350ae2 100644
--- a/src/main/java/org/shedlang/compiler/parser/TokenType.java
+++ b/src/main/java/org/shedlang/compiler/parser/TokenType.java
@@ -14,12 +14,14 @@ public enum TokenType {
     KEYWORD_FALSE,
     KEYWORD_FUN,
     KEYWORD_IF,
+    KEYWORD_IS,
     KEYWORD_RETURN,
     KEYWORD_STRUCT,
     KEYWORD_SUMTYPE,
     KEYWORD_TRUE,
     KEYWORD_VAL,
     KEYWORD_VAR,
+    KEYWORD_WHEN,
     KEYWORD_WHILE,
 
     SYMBOL_BANG,
diff --git a/src/main/java/org/shedlang/compiler/parser/Tokeniser.java b/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
index 7659d717..e7f04189 100644
--- a/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
@@ -18,12 +18,14 @@ public class Tokeniser {
         Map.entry("false", TokenType.KEYWORD_FALSE),
         Map.entry("fun", TokenType.KEYWORD_FUN),
         Map.entry("if", TokenType.KEYWORD_IF),
+        Map.entry("is", TokenType.KEYWORD_IS),
         Map.entry("return", TokenType.KEYWORD_RETURN),
         Map.entry("struct", TokenType.KEYWORD_STRUCT),
         Map.entry("sumtype", TokenType.KEYWORD_SUMTYPE),
         Map.entry("true", TokenType.KEYWORD_TRUE),
         Map.entry("val", TokenType.KEYWORD_VAL),
         Map.entry("var", TokenType.KEYWORD_VAR),
+        Map.entry("when", TokenType.KEYWORD_WHEN),
         Map.entry("while", TokenType.KEYWORD_WHILE)
     );
 
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 7c3741e2..c630b9dc 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -406,6 +406,9 @@ public class TypeChecker {
 
             case UntypedTupleNode untypedTuple ->
                 typeCheckTuple(untypedTuple, context);
+
+            case UntypedWhenNode untypedWhen ->
+                throw new UnsupportedOperationException();
         };
     }