Moved AST generation to its own package

src/build/VariableDefinition.go

@@ -77,6 +77,24 @@ func (f *Function) useVariable(variable *Variable) {
 	}
 }
 
+// identifierExists returns true if the identifier has been defined.
+func (f *Function) identifierExists(name string) bool {
+	_, exists := f.variables[name]
+
+	if exists {
+		return true
+	}
+
+	_, exists = f.definitions[name]
+
+	if exists {
+		return true
+	}
+
+	_, exists = f.functions[name]
+	return exists
+}
+
 func (f *Function) storeVariableInRegister(name string, value *expression.Expression, uses int) error {
 	reg, exists := f.cpu.FindFree(f.cpu.General)