arrays + builtins

ast/ast.go

@@ -277,3 +277,51 @@ func (sl StringLiteral) String() string {
 	return sl.Token.Literal
 }
 func (sl StringLiteral) expressionNode() {}
+
+type ArrayLiteral struct {
+	Token    token.Token // the '[' token
+	Elements []Expression
+}
+
+func (al ArrayLiteral) TokenLiteral() string {
+	return al.Token.Literal
+}
+func (al ArrayLiteral) String() string {
+	var out bytes.Buffer
+
+	elements := []string{}
+	for _, el := range al.Elements {
+		elements = append(elements, el.String())
+	}
+
+	out.WriteString("[")
+	out.WriteString(strings.Join(elements, ", "))
+	out.WriteString("]")
+
+	return out.String()
+}
+func (al ArrayLiteral) expressionNode() {}
+
+type IndexExpression struct {
+	Token token.Token // The [ token
+	Left  Expression
+	Index Expression
+}
+
+func (ie IndexExpression) TokenLiteral() string {
+	return ie.Token.Literal
+}
+
+func (ie IndexExpression) String() string {
+	var out bytes.Buffer
+
+	out.WriteString("(")
+	out.WriteString(ie.Left.String())
+	out.WriteString("[")
+	out.WriteString(ie.Index.String())
+	out.WriteString("])")
+
+	return out.String()
+}
+
+func (ie IndexExpression) expressionNode() {}

evaluator/builtins.go

@@ -10,6 +10,8 @@ var builtins = map[string]*object.Builtin{
 			}
 
 			switch arg := args[0].(type) {
+			case *object.Array:
+				return &object.Integer{Value: int64(len(arg.Elements))}
 			case *object.String:
 				return &object.Integer{Value: int64(len(arg.Value))}
 			default:
@@ -18,4 +20,82 @@ var builtins = map[string]*object.Builtin{
 			}
 		},
 	},
+
+	"first": &object.Builtin{
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `first` must be Array, got %s", args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			if len(arr.Elements) > 0 {
+				return arr.Elements[0]
+			}
+
+			return NULL
+		},
+	},
+
+	"last": &object.Builtin{
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `last` must be Array, got %s", args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			length := len(arr.Elements)
+			if length > 0 {
+				return arr.Elements[length-1]
+			}
+
+			return NULL
+		},
+	},
+
+	"rest": &object.Builtin{
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `rest` must be Array, got %s", args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			length := len(arr.Elements)
+
+			newElements := make([]object.Object, length+1)
+			copy(newElements, arr.Elements)
+			newElements[length] = args[1]
+
+			return &object.Array{Elements: newElements}
+		},
+	},
+
+	"push": &object.Builtin{
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", len(args))
+			}
+			if args[0].Type() != object.ARRAY_OBJ {
+				return newError("argument to `push` must be Array, got %s", args[0].Type())
+			}
+
+			arr := args[0].(*object.Array)
+			length := len(arr.Elements)
+			if length > 0 {
+				newElements := make([]object.Object, length-1)
+				copy(newElements, arr.Elements[1:length])
+				return &object.Array{Elements: newElements}
+			}
+
+			return NULL
+		},
+	},
 }

evaluator/evaluator.go

@@ -97,6 +97,23 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 	case *ast.StringLiteral:
 		return &object.String{Value: node.Value}
 
+	case *ast.ArrayLiteral:
+		elements := evalExpressions(node.Elements, env)
+		if len(elements) == 1 && isError(elements[0]) {
+			return elements[0]
+		}
+		return &object.Array{Elements: elements}
+
+	case *ast.IndexExpression:
+		left := Eval(node.Left, env)
+		if isError(left) {
+			return left
+		}
+		index := Eval(node.Index, env)
+		if isError(index) {
+			return index
+		}
+		return evalIndexExpression(left, index)
 	}
 
 	return nil
@@ -323,3 +340,24 @@ func unwrapReturnValue(obj object.Object) object.Object {
 
 	return obj
 }
+
+func evalIndexExpression(left, index object.Object) object.Object {
+	switch {
+	case left.Type() == object.ARRAY_OBJ && index.Type() == object.INTEGER_OBJ:
+		return evalArrayIndexExpression(left, index)
+	default:
+		return newError("index operator not supported: %s", left.Type())
+	}
+}
+
+func evalArrayIndexExpression(array, index object.Object) object.Object {
+	arrayObject := array.(*object.Array)
+	idx := index.(*object.Integer).Value
+	maxInx := int64(len(arrayObject.Elements) - 1)
+
+	if idx < 0 || idx > maxInx {
+		return NULL
+	}
+
+	return arrayObject.Elements[idx]
+}

evaluator/evaluator_test.go

@@ -357,6 +357,83 @@ func TestBuiltinFunction(t *testing.T) {
 	}
 }
 
+func TestArrayLiterals(t *testing.T) {
+	input := "[1, 2 * 2, 3 + 3]"
+
+	evaluated := testEval(input)
+	result, ok := evaluated.(*object.Array)
+	if !ok {
+		t.Fatalf("object is not Array. got=%T (+%v)", evaluated, evaluated)
+	}
+
+	if len(result.Elements) != 3 {
+		t.Fatalf("array has wrong num of elements. got=%d", evaluated)
+	}
+
+	testIntegerObject(t, result.Elements[0], 1)
+	testIntegerObject(t, result.Elements[1], 4)
+	testIntegerObject(t, result.Elements[2], 6)
+}
+
+func TestArrayIndexExpressions(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected interface{}
+	}{
+		{
+			"[1, 2, 3][0]",
+			1,
+		},
+		{
+			"[1, 2, 3][1]",
+			2,
+		},
+		{
+			"[1, 2, 3][2]",
+			3,
+		},
+		{
+			"let i = 0; [1][i];",
+			1,
+		},
+		{
+			"[1, 2, 3][1 + 1];",
+			3,
+		},
+		{
+			"let myArray = [1, 2, 3]; myArray[2];",
+			3,
+		},
+		{
+			"let myArray = [1, 2, 3]; myArray[0] + myArray[1] + myArray[2];",
+			6,
+		},
+		{
+			"let myArray = [1, 2, 3]; let i = myArray[0]; myArray[i]",
+			2,
+		},
+		{
+			"[1, 2, 3][3]",
+			nil,
+		},
+		{
+			"[1, 2, 3][-1]",
+			nil,
+		},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+
+		integer, ok := tt.expected.(int)
+		if ok {
+			testIntegerObject(t, evaluated, int64(integer))
+		} else {
+			testNullObject(t, evaluated)
+		}
+	}
+}
+
 func testEval(input string) object.Object {
 	l := lexer.New(input)
 	p := parser.New(l)

lexer/lexer.go

@@ -94,6 +94,10 @@ func (l *Lexer) NextToken() token.Token {
 	case '"':
 		tok.Type = token.STRING
 		tok.Literal = l.readString()
+	case '[':
+		tok = newToken(token.LBRACKET, l.ch)
+	case ']':
+		tok = newToken(token.RBRACKET, l.ch)
 	default:
 		if isLetter(l.ch) {
 			tok.Literal = l.readIdentifier()

lexer/lexer_test.go

@@ -27,6 +27,7 @@ func TestNextToken(t *testing.T) {
 				10 != 9;
 				"foobar"
 				"foo bar"
+				[1, 2];
 			`
 
 	tests := []struct {
@@ -117,6 +118,14 @@ func TestNextToken(t *testing.T) {
 
 		{token.STRING, "foobar"},
 		{token.STRING, "foo bar"},
+
+		{token.LBRACKET, "["},
+		{token.INT, "1"},
+		{token.COMMA, ","},
+		{token.INT, "2"},
+		{token.RBRACKET, "]"},
+		{token.SEMICOLON, ";"},
+
 		{token.EOF, ""},
 	}
 

object/object.go

@@ -18,6 +18,7 @@ const (
 	FUNCTION_OBJ     = "FUNCTION"
 	STRING_OBJ       = "STRING"
 	BUILTIN_OBJ      = "BUILTIN"
+	ARRAY_OBJ        = "ARRAY"
 )
 
 type Object interface {
@@ -133,3 +134,26 @@ func (b Builtin) Type() ObjectType {
 func (b Builtin) Inspect() string {
 	return "builtin function"
 }
+
+type Array struct {
+	Elements []Object
+}
+
+func (ao Array) Type() ObjectType {
+	return ARRAY_OBJ
+}
+
+func (ao Array) Inspect() string {
+	var out bytes.Buffer
+
+	elements := []string{}
+	for _, e := range ao.Elements {
+		elements = append(elements, e.Inspect())
+	}
+
+	out.WriteString("[")
+	out.WriteString(strings.Join(elements, ", "))
+	out.WriteString("]")
+
+	return out.String()
+}

parser/parser.go

@@ -30,6 +30,7 @@ var precedences = map[token.TokenType]int{
 	token.SLASH:    PRODUCT,
 	token.ASTERISK: PRODUCT,
 	token.LPAREN:   CALL,
+	token.LBRACKET: INDEX,
 }
 
 type (
@@ -65,6 +66,7 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerPrefix(token.IF, p.parseIfExpression)
 	p.registerPrefix(token.FUNCTION, p.parseFunctionLiteral)
 	p.registerPrefix(token.STRING, p.parseStringLiteral)
+	p.registerPrefix(token.LBRACKET, p.parseArrayLiteral)
 
 	p.infixParseFns = make(map[token.TokenType]infixParseFn)
 	p.registerInfix(token.PLUS, p.parseInfixExpression)
@@ -75,8 +77,8 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerInfix(token.NOT_EQ, p.parseInfixExpression)
 	p.registerInfix(token.LT, p.parseInfixExpression)
 	p.registerInfix(token.GT, p.parseInfixExpression)
-
 	p.registerInfix(token.LPAREN, p.parseCallExpression)
+	p.registerInfix(token.LBRACKET, p.parseIndexExpression)
 
 	// Read two tokens, so curToken and peekToken are both set
 	p.nextToken()
@@ -435,3 +437,24 @@ func (p *Parser) registerInfix(tokenType token.TokenType, fn infixParseFn) {
 func (p *Parser) parseStringLiteral() ast.Expression {
 	return &ast.StringLiteral{Token: p.curToken, Value: p.curToken.Literal}
 }
+
+func (p *Parser) parseArrayLiteral() ast.Expression {
+	array := &ast.ArrayLiteral{Token: p.curToken}
+
+	array.Elements = p.parseExpressionList(token.RBRACKET)
+
+	return array
+}
+
+func (p *Parser) parseIndexExpression(left ast.Expression) ast.Expression {
+	exp := &ast.IndexExpression{Token: p.curToken, Left: left}
+
+	p.nextToken()
+	exp.Index = p.parseExpression(LOWEST)
+
+	if !p.expectPeek(token.RBRACKET) {
+		return nil
+	}
+
+	return exp
+}

parser/parser_test.go

@@ -341,6 +341,14 @@ func TestOperatorPrecedenceParsing(t *testing.T) {
 			"add(a + b + c * d / f + g)",
 			"add((((a + b) + ((c * d) / f)) + g))",
 		},
+		{
+			"a * [1, 2, 3, 4][b * c] * d",
+			"((a * ([1, 2, 3, 4][(b * c)])) * d)",
+		},
+		{
+			"add(a * b[2], b[1], 2 * [1, 2][1])",
+			"add((a * (b[2])), (b[1]), (2 * ([1, 2][1])))",
+		},
 	}
 
 	for _, tt := range tests {
@@ -689,6 +697,52 @@ func TestStringLiteralExpression(t *testing.T) {
 	}
 }
 
+func TestParsingArrayLiterals(t *testing.T) {
+	input := "[1, 2 * 2, 3 + 3]"
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	stmt := program.Statements[0].(*ast.ExpressionStatement)
+	array, ok := stmt.Expression.(*ast.ArrayLiteral)
+	if !ok {
+		t.Fatalf("exp not *ast.ArrayLiteral. got=%T", stmt.Expression)
+	}
+
+	if len(array.Elements) != 3 {
+		t.Fatalf("len(array.Elements) not 3. got=%d", len(array.Elements))
+	}
+
+	testIntegerLiteral(t, array.Elements[0], 1)
+	testInfixExpression(t, array.Elements[1], 2, "*", 2)
+	testInfixExpression(t, array.Elements[2], 3, "+", 3)
+}
+
+func TestParsingIndexExpressions(t *testing.T) {
+	input := "myArray[1 + 1]"
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	stmt := program.Statements[0].(*ast.ExpressionStatement)
+	indexExp, ok := stmt.Expression.(*ast.IndexExpression)
+	if !ok {
+		t.Fatalf("exp not *ast.IndexExpression. got=%T", stmt.Expression)
+	}
+
+	if !testIdentifier(t, indexExp.Left, "myArray") {
+		return
+	}
+
+	if !testInfixExpression(t, indexExp.Index, 1, "+", 1) {
+		return
+	}
+}
+
 func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
 	if s.TokenLiteral() != "let" {
 		t.Errorf("s.TokenLiteral not 'let'. got=%q", s.TokenLiteral())

token/token.go

@@ -38,6 +38,8 @@ const (
 	RPAREN   = ")"
 	LBRACE   = "{"
 	RBRACE   = "}"
+	LBRACKET = "["
+	RBRACKET = "]"
 
 	// Keywords
 	FUNCTION = "FUNCTION"