Check that condition is a boolean

2 files changed, 19 insertions, 2 deletions

diff --git a/src/main/java/org/zwobble/couscous/interpreter/ConditionMustBeBoolean.java b/src/main/java/org/zwobble/couscous/interpreter/ConditionMustBeBoolean.java
new file mode 100644
index 0000000..c69c290
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/ConditionMustBeBoolean.java
@@ -0,0 +1,14 @@
+package org.zwobble.couscous.interpreter;
+
+import org.zwobble.couscous.values.InterpreterValue;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+
+@Value
+@EqualsAndHashCode(callSuper=false)
+public class ConditionMustBeBoolean extends InterpreterException {
+    private static final long serialVersionUID = 1L;
+
+    InterpreterValue actual;
+}
diff --git a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
index 6586f6a..232441c 100644
--- a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
+++ b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
@@ -45,8 +45,11 @@ public class Evaluator implements ExpressionNodeVisitor<InterpreterValue> {
 
     @Override
     public InterpreterValue visit(TernaryConditionalNode ternaryConditional) {
-        val condition = (BooleanValue)eval(ternaryConditional.getCondition());
-        val branch = condition.getValue()
+        val condition = eval(ternaryConditional.getCondition());
+        if (!(condition instanceof BooleanValue)) {
+            throw new ConditionMustBeBoolean(condition);
+        }
+        val branch = ((BooleanValue)condition).getValue()
             ? ternaryConditional.getIfTrue()
             : ternaryConditional.getIfFalse();
         return eval(branch);