Hashes

ast/ast.go

@@ -325,3 +325,29 @@ func (ie IndexExpression) String() string {
 }
 
 func (ie IndexExpression) expressionNode() {}
+
+type HashLiteral struct {
+	Token token.Token // the '{' token
+	Pairs map[Expression]Expression
+}
+
+func (hl HashLiteral) TokenLiteral() string {
+	return hl.Token.Literal
+}
+
+func (hl HashLiteral) String() string {
+	var out bytes.Buffer
+
+	pairs := []string{}
+	for key, value := range hl.Pairs {
+		pairs = append(pairs, key.String()+":"+value.String())
+	}
+
+	out.WriteString("{")
+	out.WriteString(strings.Join(pairs, ", "))
+	out.WriteString("}")
+
+	return out.String()
+}
+
+func (hl HashLiteral) expressionNode() {}

evaluator/evaluator.go

@@ -114,6 +114,10 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 			return index
 		}
 		return evalIndexExpression(left, index)
+
+	case *ast.HashLiteral:
+		return evalHashLiteral(node, env)
+
 	}
 
 	return nil
@@ -345,11 +349,29 @@ func evalIndexExpression(left, index object.Object) object.Object {
 	switch {
 	case left.Type() == object.ARRAY_OBJ && index.Type() == object.INTEGER_OBJ:
 		return evalArrayIndexExpression(left, index)
+	case left.Type() == object.HASH_OBJ:
+		return evalHashIndexExpression(left, index)
 	default:
 		return newError("index operator not supported: %s", left.Type())
 	}
 }
 
+func evalHashIndexExpression(hash, index object.Object) object.Object {
+	hashObject := hash.(*object.Hash)
+
+	key, ok := index.(object.Hashable)
+	if !ok {
+		return newError("unusable as hash key: %s", index.Type())
+	}
+
+	pair, ok := hashObject.Pairs[key.HashKey()]
+	if !ok {
+		return NULL
+	}
+
+	return pair.Value
+}
+
 func evalArrayIndexExpression(array, index object.Object) object.Object {
 	arrayObject := array.(*object.Array)
 	idx := index.(*object.Integer).Value
@@ -361,3 +383,32 @@ func evalArrayIndexExpression(array, index object.Object) object.Object {
 
 	return arrayObject.Elements[idx]
 }
+
+func evalHashLiteral(node *ast.HashLiteral, env *object.Environment) object.Object {
+	pairs := make(map[object.HashKey]object.HashPair)
+
+	for keyNode, valueNode := range node.Pairs {
+		key := Eval(keyNode, env)
+		if isError(key) {
+			return key
+		}
+
+		hashKey, ok := key.(object.Hashable)
+		if !ok {
+			return newError("unusable as hash key: %s", key.Type())
+		}
+
+		value := Eval(valueNode, env)
+		if isError(value) {
+			return value
+		}
+
+		hashed := hashKey.HashKey()
+		pairs[hashed] = object.HashPair{
+			Key:   key,
+			Value: value,
+		}
+	}
+
+	return &object.Hash{Pairs: pairs}
+}

evaluator/evaluator_test.go

@@ -209,6 +209,10 @@ func TestErrorHandling(t *testing.T) {
 			`"Hello" - "World"`,
 			"unknown operator: STRING - STRING",
 		},
+		{
+			`{"name": "Monkey"}[fn(x) { x }];`,
+			"unusable as hash key: FUNCTION",
+		},
 	}
 
 	for _, tt := range tests {
@@ -434,6 +438,93 @@ func TestArrayIndexExpressions(t *testing.T) {
 	}
 }
 
+func TestHashLiterals(t *testing.T) {
+	input := `let two = "two";
+    {
+        "one": 10 - 9,
+        two: 1 + 1,
+        "thr" + "ee": 6 / 2,
+        4: 4,
+        true: 5,
+        false: 6
+    }`
+
+	evaluated := testEval(input)
+	result, ok := evaluated.(*object.Hash)
+	if !ok {
+		t.Fatalf("Eval didn't return Hash. got=%T (%+v)", evaluated, evaluated)
+	}
+
+	expected := map[object.HashKey]int64{
+		(&object.String{Value: "one"}).HashKey():   1,
+		(&object.String{Value: "two"}).HashKey():   2,
+		(&object.String{Value: "three"}).HashKey(): 3,
+		(&object.Integer{Value: 4}).HashKey():      4,
+		TRUE.HashKey():                             5,
+		FALSE.HashKey():                            6,
+	}
+
+	if len(result.Pairs) != len(expected) {
+		t.Fatalf("Hash has wrong num of pair. got=%d", len(result.Pairs))
+	}
+
+	for expectedKey, expectedValue := range expected {
+		pair, ok := result.Pairs[expectedKey]
+		if !ok {
+			t.Errorf("no pair for given key in Pairs")
+		}
+
+		testIntegerObject(t, pair.Value, expectedValue)
+	}
+}
+
+func TestHashIndexExpressions(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected interface{}
+	}{
+		{
+			`{"foo": 5}["foo"]`,
+			5,
+		},
+		{
+			`{"foo": 5}["bar"]`,
+			nil,
+		},
+		{
+			`let key = "foo"; {"foo": 5}[key]`,
+			5,
+		},
+		{
+			`{}["foo"]`,
+			nil,
+		},
+		{
+			`{5: 5}[5]`,
+			5,
+		},
+		{
+			`{true: 5}[true]`,
+			5,
+		},
+		{
+			`{false: 5}[false]`,
+			5,
+		},
+	}
+
+	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

@@ -98,6 +98,8 @@ func (l *Lexer) NextToken() token.Token {
 		tok = newToken(token.LBRACKET, l.ch)
 	case ']':
 		tok = newToken(token.RBRACKET, l.ch)
+	case ':':
+		tok = newToken(token.COLON, l.ch)
 	default:
 		if isLetter(l.ch) {
 			tok.Literal = l.readIdentifier()

lexer/lexer_test.go

@@ -28,6 +28,7 @@ func TestNextToken(t *testing.T) {
 				"foobar"
 				"foo bar"
 				[1, 2];
+				{"foo": "bar"}
 			`
 
 	tests := []struct {
@@ -126,6 +127,12 @@ func TestNextToken(t *testing.T) {
 		{token.RBRACKET, "]"},
 		{token.SEMICOLON, ";"},
 
+		{token.LBRACE, "{"},
+		{token.STRING, "foo"},
+		{token.COLON, ":"},
+		{token.STRING, "bar"},
+		{token.RBRACE, "}"},
+
 		{token.EOF, ""},
 	}
 

object/object.go

@@ -3,6 +3,7 @@ package object
 import (
 	"bytes"
 	"fmt"
+	"hash/fnv"
 	"monkey/ast"
 	"strings"
 )
@@ -19,6 +20,7 @@ const (
 	STRING_OBJ       = "STRING"
 	BUILTIN_OBJ      = "BUILTIN"
 	ARRAY_OBJ        = "ARRAY"
+	HASH_OBJ         = "HASH"
 )
 
 type Object interface {
@@ -157,3 +159,63 @@ func (ao Array) Inspect() string {
 
 	return out.String()
 }
+
+type HashKey struct {
+	Type  ObjectType
+	Value uint64
+}
+
+func (b *Boolean) HashKey() HashKey {
+	var value uint64
+
+	if b.Value {
+		value = 1
+	} else {
+		value = 0
+	}
+
+	return HashKey{Type: b.Type(), Value: value}
+}
+
+type Hashable interface {
+	HashKey() HashKey
+}
+
+func (i *Integer) HashKey() HashKey {
+	return HashKey{Type: i.Type(), Value: uint64(i.Value)}
+}
+
+func (s *String) HashKey() HashKey {
+	h := fnv.New64a()
+	h.Write([]byte(s.Value))
+
+	return HashKey{Type: s.Type(), Value: h.Sum64()}
+}
+
+type HashPair struct {
+	Key   Object
+	Value Object
+}
+
+type Hash struct {
+	Pairs map[HashKey]HashPair
+}
+
+func (h *Hash) Type() ObjectType {
+	return HASH_OBJ
+}
+
+func (h *Hash) Inspect() string {
+	var out bytes.Buffer
+
+	pairs := []string{}
+	for _, pair := range h.Pairs {
+		pairs = append(pairs, fmt.Sprintf("%s: %s", pair.Key.Inspect(), pair.Value.Inspect()))
+	}
+
+	out.WriteString("{")
+	out.WriteString(strings.Join(pairs, ", "))
+	out.WriteString("}")
+
+	return out.String()
+}

object/object_test.go

@@ -0,0 +1,22 @@
+package object
+
+import "testing"
+
+func TestStringHashKey(t *testing.T) {
+	hello1 := &String{Value: "Hello World"}
+	hello2 := &String{Value: "Hello World"}
+	diff1 := &String{Value: "My name is johnny"}
+	diff2 := &String{Value: "My name is johnny"}
+
+	if hello1.HashKey() != hello2.HashKey() {
+		t.Errorf("string with same content have different hash keys")
+	}
+
+	if diff1.HashKey() != diff2.HashKey() {
+		t.Errorf("string with same content have different hash keys")
+	}
+
+	if hello1.HashKey() == diff1.HashKey() {
+		t.Errorf("string with different content have same hash keys")
+	}
+}

parser/parser.go

@@ -67,6 +67,7 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerPrefix(token.FUNCTION, p.parseFunctionLiteral)
 	p.registerPrefix(token.STRING, p.parseStringLiteral)
 	p.registerPrefix(token.LBRACKET, p.parseArrayLiteral)
+	p.registerPrefix(token.LBRACE, p.parseHashLiteral)
 
 	p.infixParseFns = make(map[token.TokenType]infixParseFn)
 	p.registerInfix(token.PLUS, p.parseInfixExpression)
@@ -458,3 +459,32 @@ func (p *Parser) parseIndexExpression(left ast.Expression) ast.Expression {
 
 	return exp
 }
+
+func (p *Parser) parseHashLiteral() ast.Expression {
+	hash := &ast.HashLiteral{Token: p.curToken}
+	hash.Pairs = make(map[ast.Expression]ast.Expression)
+
+	for !p.peekTokenIs(token.RBRACE) {
+		p.nextToken()
+		key := p.parseExpression(LOWEST)
+
+		if !p.expectPeek(token.COLON) {
+			return nil
+		}
+
+		p.nextToken()
+		value := p.parseExpression(LOWEST)
+
+		hash.Pairs[key] = value
+
+		if !p.peekTokenIs(token.RBRACE) && !p.expectPeek(token.COMMA) {
+			return nil
+		}
+	}
+
+	if !p.expectPeek(token.RBRACE) {
+		return nil
+	}
+
+	return hash
+}

parser/parser_test.go

@@ -743,6 +743,108 @@ func TestParsingIndexExpressions(t *testing.T) {
 	}
 }
 
+func TestParsingHashLiteralsStringKeys(t *testing.T) {
+	input := `{"one": 1, "two": 2, "three": 3}`
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	stmt := program.Statements[0].(*ast.ExpressionStatement)
+	hash, ok := stmt.Expression.(*ast.HashLiteral)
+	if !ok {
+		t.Fatalf("exp not *ast.HashLiteral. got=%T", stmt.Expression)
+	}
+
+	if len(hash.Pairs) != 3 {
+		t.Fatalf("hash.Pairs has wrong length. got=%d", len(hash.Pairs))
+	}
+
+	expected := map[string]int64{
+		"one":   1,
+		"two":   2,
+		"three": 3,
+	}
+
+	for key, value := range hash.Pairs {
+		literal, ok := key.(*ast.StringLiteral)
+		if !ok {
+			t.Errorf("key is not ast.StringLiteral. got=%T", key)
+		}
+
+		expectedValue := expected[literal.String()]
+
+		testIntegerLiteral(t, value, expectedValue)
+	}
+}
+
+func TestParsingEmptyHashLiteral(t *testing.T) {
+	input := "{}"
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	stmt := program.Statements[0].(*ast.ExpressionStatement)
+	hash, ok := stmt.Expression.(*ast.HashLiteral)
+	if !ok {
+		t.Fatalf("exp not *ast.HashLiteral. got=%T", stmt.Expression)
+	}
+
+	if len(hash.Pairs) != 0 {
+		t.Errorf("hash.Pairs has wrong length. got=%d", len(hash.Pairs))
+	}
+}
+
+func TestParsingHashLiteralsWithExpressions(t *testing.T) {
+	input := `{"one": 0 + 1, "two": 10 - 8, "three": 15 / 5}`
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	stmt := program.Statements[0].(*ast.ExpressionStatement)
+	hash, ok := stmt.Expression.(*ast.HashLiteral)
+	if !ok {
+		t.Fatalf("exp not *ast.HashLiteral. got=%T", stmt.Expression)
+	}
+
+	if len(hash.Pairs) != 3 {
+		t.Fatalf("hash.Pairs has wrong length. got=%d", len(hash.Pairs))
+	}
+
+	tests := map[string]func(expression ast.Expression){
+		"one": func(e ast.Expression) {
+			testInfixExpression(t, e, 0, "+", 1)
+		},
+		"two": func(e ast.Expression) {
+			testInfixExpression(t, e, 10, "-", 8)
+		},
+		"three": func(e ast.Expression) {
+			testInfixExpression(t, e, 15, "/", 5)
+		},
+	}
+
+	for key, value := range hash.Pairs {
+		literal, ok := key.(*ast.StringLiteral)
+		if !ok {
+			t.Errorf("key is not ast.StringLiteral. got=%T", key)
+			continue
+		}
+
+		testFunc, ok := tests[literal.String()]
+		if !ok {
+			t.Errorf("No test function for key %q found", literal.String())
+			continue
+		}
+
+		testFunc(value)
+	}
+}
+
 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

@@ -33,6 +33,7 @@ const (
 	// Delimiters
 	COMMA     = ","
 	SEMICOLON = ";"
+	COLON     = ":"
 
 	LPAREN   = "("
 	RPAREN   = ")"