Fix trait method lookup for multi-trait classes (#133)

* fix trait method lookup

* allow multiple traits on class

Author: kaidesu

CLAUDE.md

@@ -0,0 +1,46 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build and Development Commands
+
+```bash
+make run        # Build and run Ghost REPL
+make build      # Build for all platforms (mac/linux/windows)
+make test       # Run all tests with colored output
+go test -v ./evaluator/...  # Run tests for a specific package
+```
+
+## Architecture Overview
+
+Ghost is a tree-walking interpreter written in Go. The execution pipeline follows this flow:
+
+**Source Code → Scanner → Parser → AST → Evaluator → Object**
+
+### Core Packages
+
+- **scanner/** - Lexical analysis. Transforms source into tokens. Keywords defined in `scanner/scanner.go:21-48`.
+- **token/** - Token type definitions and the Token struct containing lexeme, literal, position info.
+- **parser/** - Recursive descent parser using Pratt parsing. Each AST node type has its own parsing function (e.g., `parser/function.go`, `parser/if.go`).
+- **ast/** - Abstract syntax tree node definitions. Base interfaces in `ast/ast.go`: `Node`, `StatementNode`, `ExpressionNode`.
+- **evaluator/** - Tree-walking evaluation. Main entry point is `Evaluate()` in `evaluator/evaluator.go:15`. Each AST node type has a corresponding `evaluate*` function.
+- **object/** - Runtime value types (Number, String, Boolean, List, Map, Function, Class, etc.). The `Object` interface (`object/object.go:15-19`) requires `Type()`, `String()`, and `Method()`.
+- **ghost/** - Main Ghost struct that orchestrates the pipeline (`ghost/ghost.go`). Entry point for embedding Ghost in Go applications.
+
+### Key Design Patterns
+
+- **Scope**: Wraps Environment and tracks `Self` for method calls (`object/scope.go`).
+- **Environment**: Variable storage with parent chain for lexical scoping (`object/environment.go`).
+- **Library system**: Native functions and modules registered via `library.RegisterFunction()` and `library.RegisterModule()`. Built-in modules in `library/modules/`.
+
+### Object Method System
+
+All object types implement the `Method(method string, args []Object) (Object, bool)` interface. Methods are defined directly on object types (e.g., string methods in `object/string.go`).
+
+## Language Features
+
+Ghost supports: classes with inheritance (`extends`), traits (`trait`/`use`), first-class functions, closures, lists, maps, for/for-in/while loops, switch statements, imports, and compound operators (`+=`, `++`, etc.).
+
+## Version
+
+Update `version/version.go` when releasing. GoReleaser handles binary distribution.

evaluator/evaluator_test.go

@@ -207,7 +207,7 @@ func TestClassProperties(t *testing.T) {
 		function constructor(area) {
 			this.area = area
 		}
-	
+
 		function area() {
 			return math.pi * this.area * this.area
 		}
@@ -223,6 +223,90 @@ func TestClassProperties(t *testing.T) {
 	isNumberObject(t, result, 314)
 }
 
+func TestTraitMethodLookup(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected int64
+	}{
+		{
+			name: "method from single trait",
+			input: `
+				trait Greet {
+					function greet() {
+						return 1
+					}
+				}
+
+				class Person {
+					use Greet
+				}
+
+				p = Person.new()
+				p.greet()
+			`,
+			expected: 1,
+		},
+		{
+			name: "method from second trait",
+			input: `
+				trait First {
+					function first() {
+						return 1
+					}
+				}
+
+				trait Second {
+					function second() {
+						return 2
+					}
+				}
+
+				class Thing {
+					use First
+					use Second
+				}
+
+				t = Thing.new()
+				t.second()
+			`,
+			expected: 2,
+		},
+		{
+			name: "methods from both traits",
+			input: `
+				trait Add {
+					function add() {
+						return 10
+					}
+				}
+
+				trait Multiply {
+					function multiply() {
+						return 20
+					}
+				}
+
+				class Calculator {
+					use Add
+					use Multiply
+				}
+
+				c = Calculator.new()
+				c.add() + c.multiply()
+			`,
+			expected: 30,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := evaluate(tt.input)
+			isNumberObject(t, result, tt.expected)
+		})
+	}
+}
+
 // =============================================================================
 // Helper functions
 

evaluator/method.go

@@ -79,8 +79,8 @@ func evaluateInstanceMethod(node *ast.Method, receiver *object.Instance, name st
 		for _, trait := range receiver.Class.Traits {
 			method, ok = trait.Environment.Get(name)
 
-			if !ok {
-				return object.NewError("%d:%d:%s: runtime error: undefined method %s for class %s", node.Token.Line, node.Token.Column, node.Token.File, name, receiver.Class.Name.Value)
+			if ok {
+				break
 			}
 		}
 	}

evaluator/use.go

@@ -31,7 +31,7 @@ func evaluateUse(node *ast.Use, scope *object.Scope) object.Object {
 		traits = append(traits, t)
 	}
 
-	class.Traits = traits
+	class.Traits = append(class.Traits, traits...)
 
 	return nil
 }