Check expression is tuple

5 files changed, 47 insertions, 3 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index eafa9f47..435de6de 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -865,7 +865,14 @@ public class TypeChecker {
             }
 
             case UntypedTargetNode.Tuple targetTuple -> {
-                var tupleType = (TupleType) expressionType;
+                if (!(expressionType instanceof TupleType tupleType)) {
+                    throw new UnexpectedTypeError(
+                        TypeSets.TUPLE,
+                        expressionType,
+                        // TODO: should the source be the target or the expression?
+                        targetTuple.source()
+                    );
+                }
 
                 var typedTargetElements = new ArrayList<TypedTargetNode>();
 
diff --git a/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSet.java b/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSet.java
index 01899978..5a0350f4 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSet.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSet.java
@@ -1,5 +1,5 @@
 package org.shedlang.compiler.typechecker.typesets;
 
-public sealed interface TypeSet permits TypeSetFunction, TypeSetType, TypeSetTypeLevelValue {
+public sealed interface TypeSet permits TypeSetFunction, TypeSetTuple, TypeSetType, TypeSetTypeLevelValue {
     String describe();
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSetTuple.java b/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSetTuple.java
new file mode 100644
index 00000000..dc8773b5
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSetTuple.java
@@ -0,0 +1,13 @@
+package org.shedlang.compiler.typechecker.typesets;
+
+public final class TypeSetTuple implements TypeSet {
+    static final TypeSetTuple INSTANCE = new TypeSetTuple();
+
+    private TypeSetTuple() {
+    }
+
+    @Override
+    public String describe() {
+        return "tuple";
+    }
+}
diff --git a/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSets.java b/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSets.java
index 3dd47cae..6b6d2d69 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSets.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/typesets/TypeSets.java
@@ -9,6 +9,7 @@ public class TypeSets {
     public static final TypeSetEffect EFFECT = TypeSetEffect.INSTANCE;
     public static final TypeSet FUNCTION = TypeSetFunction.INSTANCE;
     public static final TypeSetMetaType META_TYPE = TypeSetMetaType.INSTANCE;
+    public static final TypeSetTuple TUPLE = TypeSetTuple.INSTANCE;
 
     public static TypeSet type(Type type) {
         return new TypeSetType(type);
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java
index 20f3ef5d..b71db8f7 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerAssignTests.java
@@ -85,7 +85,7 @@ public class TypeCheckerAssignTests {
         ));
         var context = TypeCheckerContext.EMPTY
             .enterNamespace(P.map(
-                Map.entry("x", Variable.defined(tupleType, VariableType.VAR))
+                Map.entry("x", Variable.defined(tupleType, VariableType.VAL))
             ));
 
         var typed = typeCheckFunctionStatement(untyped, context);
@@ -100,6 +100,29 @@ public class TypeCheckerAssignTests {
         ));
     }
 
+    @Test
+    public void givenExpressionIsNotTupleWhenTargetIsTupleThenErrorIsThrown() {
+        var untyped = Untyped.assign(
+            Untyped.targetTuple(List.of(
+                Untyped.targetVal("a"),
+                Untyped.targetVal("b")
+            )),
+            Untyped.reference("x")
+        );
+        var context = TypeCheckerContext.EMPTY
+            .enterNamespace(P.map(
+                Map.entry("x", Variable.defined(Types.INT, VariableType.VAL))
+            ));
+
+        var error = assertThrows(
+            UnexpectedTypeError.class,
+            () -> typeCheckFunctionStatement(untyped, context)
+        );
+
+        assertThat(error.actual(), equalTo(Types.INT));
+        assertThat(error.expected(), equalTo(TypeSets.TUPLE));
+    }
+
     private static TypeCheckerResult<? extends TypedFunctionStatementNode> typeCheckFunctionStatement(
         UntypedFunctionStatementNode untyped,
         TypeCheckerContext context