Check assignment is to var

2 files changed, 24 insertions, 8 deletions

diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 0828e59a..5a3ee7a7 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -52,14 +52,16 @@ public class TypeChecker {
             .orElseThrow(() -> new ReferenceBeforeDefinitionError(name, source));
     }
 
-    private static TypeCheckerResult<Type> runtimeLookup(String name, Source source, TypeCheckerContext context) {
+    private static TypeCheckerResult<Variable> runtimeLookup(String name, Source source, TypeCheckerContext context) {
         return context.runtimeLookup(name, source).map(variable -> {
             if (variable.isEmpty()) {
                 throw new UnknownVariableError(name, source);
             }
 
-            return variable.get().type()
+            variable.get().type()
                 .orElseThrow(() -> new ReferenceBeforeDefinitionError(name, source));
+
+            return variable.get();
         });
     }
 
@@ -738,10 +740,10 @@ public class TypeChecker {
         UntypedReferenceNode untyped,
         TypeCheckerContext context
     ) {
-        return runtimeLookup(untyped.name(), untyped.source(), context).map(type -> {
+        return runtimeLookup(untyped.name(), untyped.source(), context).map(variable -> {
             return new TypedReferenceNode(
                 untyped.name(),
-                type,
+                variable.type().orElseThrow(),
                 untyped.source()
             );
         });
@@ -850,17 +852,21 @@ public class TypeChecker {
         return switch (target) {
             case UntypedTargetNode.Variable variable -> {
                 if (variableType.isEmpty()) {
-                    var targetTypeResult = runtimeLookup(
+                    var targetVariableResult = runtimeLookup(
                         variable.name(),
                         variable.source(),
                         context
                     );
-                    var targetType = targetTypeResult.value();
-                    context = targetTypeResult.context();
+                    var targetVariable = targetVariableResult.value();
+                    context = targetVariableResult.context();
+
+                    if (targetVariable.variableType() != VariableType.VAR) {
+                        throw new CanOnlyAssignToVarError(target.source());
+                    }
 
                     checkIsSubType(
                         expressionType,
-                        targetType,
+                        targetVariable.type().orElseThrow(),
                         target.source(),
                         context
                     );
diff --git a/src/main/java/org/shedlang/compiler/typechecker/errors/CanOnlyAssignToVarError.java b/src/main/java/org/shedlang/compiler/typechecker/errors/CanOnlyAssignToVarError.java
new file mode 100644
index 00000000..ebfbc140
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/errors/CanOnlyAssignToVarError.java
@@ -0,0 +1,10 @@
+package org.shedlang.compiler.typechecker.errors;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+
+public class CanOnlyAssignToVarError extends SourceError {
+    public CanOnlyAssignToVarError(Source source) {
+        super("Can only assign to var", source);
+    }
+}