Error if trying to assign to variable not in scope

1 files changed, 29 insertions, 0 deletions

diff --git a/src/main/java/org/zwobble/couscous/interpreter/StackFrameBuilder.java b/src/main/java/org/zwobble/couscous/interpreter/StackFrameBuilder.java
new file mode 100644
index 0000000..ac425cd
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/StackFrameBuilder.java
@@ -0,0 +1,29 @@
+package org.zwobble.couscous.interpreter;
+
+import java.util.Map;
+
+import org.zwobble.couscous.ast.VariableNode;
+import org.zwobble.couscous.values.InterpreterValue;
+
+import com.google.common.collect.ImmutableMap;
+
+import java.util.Optional;
+
+public class StackFrameBuilder {
+    private final ImmutableMap.Builder<Integer, Optional<InterpreterValue>> variables
+        = ImmutableMap.builder();
+    
+    public StackFrameBuilder declare(VariableNode variable, InterpreterValue value) {
+        variables.put(variable.getId(), Optional.of(value));
+        return this;
+    }
+    
+    public StackFrameBuilder declare(VariableNode variable) {
+        variables.put(variable.getId(), Optional.empty());
+        return this;
+    }
+    
+    public Map<Integer, Optional<InterpreterValue>> build() {
+        return variables.build();
+    }
+}