bind expression (:=) instead of let

ast/ast.go

@@ -47,31 +47,6 @@ func (p *Program) String() string {
 	return out.String()
 }
 
-// Statements
-type LetStatement struct {
-	Token token.Token // the token.LET token
-	Name  *Identifier
-	Value Expression
-}
-
-func (ls *LetStatement) statementNode()       {}
-func (ls *LetStatement) TokenLiteral() string { return ls.Token.Literal }
-func (ls *LetStatement) String() string {
-	var out bytes.Buffer
-
-	out.WriteString(ls.TokenLiteral() + " ")
-	out.WriteString(ls.Name.String())
-	out.WriteString(" = ")
-
-	if ls.Value != nil {
-		out.WriteString(ls.Value.String())
-	}
-
-	out.WriteString(";")
-
-	return out.String()
-}
-
 type ReturnStatement struct {
 	Token       token.Token // the 'return' token
 	ReturnValue Expression
@@ -284,23 +259,23 @@ type StringLiteral struct {
 	Value string
 }
 
-func (sl StringLiteral) TokenLiteral() string {
+func (sl *StringLiteral) TokenLiteral() string {
 	return sl.Token.Literal
 }
-func (sl StringLiteral) String() string {
+func (sl *StringLiteral) String() string {
 	return sl.Token.Literal
 }
-func (sl StringLiteral) expressionNode() {}
+func (sl *StringLiteral) expressionNode() {}
 
 type ArrayLiteral struct {
 	Token    token.Token // the '[' token
 	Elements []Expression
 }
 
-func (al ArrayLiteral) TokenLiteral() string {
+func (al *ArrayLiteral) TokenLiteral() string {
 	return al.Token.Literal
 }
-func (al ArrayLiteral) String() string {
+func (al *ArrayLiteral) String() string {
 	var out bytes.Buffer
 
 	elements := []string{}
@@ -314,7 +289,7 @@ func (al ArrayLiteral) String() string {
 
 	return out.String()
 }
-func (al ArrayLiteral) expressionNode() {}
+func (al *ArrayLiteral) expressionNode() {}
 
 type IndexExpression struct {
 	Token token.Token // The [ token
@@ -322,11 +297,11 @@ type IndexExpression struct {
 	Index Expression
 }
 
-func (ie IndexExpression) TokenLiteral() string {
+func (ie *IndexExpression) TokenLiteral() string {
 	return ie.Token.Literal
 }
 
-func (ie IndexExpression) String() string {
+func (ie *IndexExpression) String() string {
 	var out bytes.Buffer
 
 	out.WriteString("(")
@@ -338,18 +313,18 @@ func (ie IndexExpression) String() string {
 	return out.String()
 }
 
-func (ie IndexExpression) expressionNode() {}
+func (ie *IndexExpression) expressionNode() {}
 
 type HashLiteral struct {
 	Token token.Token // the '{' token
 	Pairs map[Expression]Expression
 }
 
-func (hl HashLiteral) TokenLiteral() string {
+func (hl *HashLiteral) TokenLiteral() string {
 	return hl.Token.Literal
 }
 
-func (hl HashLiteral) String() string {
+func (hl *HashLiteral) String() string {
 	var out bytes.Buffer
 
 	pairs := []string{}
@@ -364,7 +339,7 @@ func (hl HashLiteral) String() string {
 	return out.String()
 }
 
-func (hl HashLiteral) expressionNode() {}
+func (hl *HashLiteral) expressionNode() {}
 
 type WhileExpression struct {
 	Token       token.Token // The 'while' token
@@ -389,6 +364,28 @@ func (we *WhileExpression) String() string {
 	return out.String()
 }
 
+// BindExpression represents an assignment expression of the form:
+// x := 1
+type BindExpression struct {
+	Token token.Token // the := token
+	Left  Expression
+	Value Expression
+}
+
+func (be *BindExpression) TokenLiteral() string {
+	return be.Token.Literal
+}
+func (be *BindExpression) String() string {
+	var out bytes.Buffer
+
+	out.WriteString(be.Left.String())
+	out.WriteString(be.TokenLiteral())
+	out.WriteString(be.Value.String())
+
+	return out.String()
+}
+func (be *BindExpression) expressionNode() {}
+
 // AssignmentExpression represents an assignment expression of the form:
 // x = 1 or xs[1] = 2
 type AssignmentExpression struct {
@@ -397,10 +394,10 @@ type AssignmentExpression struct {
 	Value Expression
 }
 
-func (as AssignmentExpression) TokenLiteral() string {
+func (as *AssignmentExpression) TokenLiteral() string {
 	return as.Token.Literal
 }
-func (as AssignmentExpression) String() string {
+func (as *AssignmentExpression) String() string {
 	var out bytes.Buffer
 
 	out.WriteString(as.Left.String())
@@ -409,7 +406,7 @@ func (as AssignmentExpression) String() string {
 
 	return out.String()
 }
-func (as AssignmentExpression) expressionNode() {}
+func (as *AssignmentExpression) expressionNode() {}
 
 // Comment a comment
 type Comment struct {

ast/ast_test.go

@@ -1,6 +1,7 @@
 package ast
 
 import (
+	"github.com/stretchr/testify/assert"
 	"monkey/token"
 	"testing"
 )
@@ -8,21 +9,22 @@ import (
 func TestString(t *testing.T) {
 	program := &Program{
 		Statements: []Statement{
-			&LetStatement{
-				Token: token.Token{Type: token.LET, Literal: "let"},
-				Name: &Identifier{
-					Token: token.Token{Type: token.IDENT, Literal: "myVar"},
-					Value: "myVar",
-				},
-				Value: &Identifier{
-					Token: token.Token{Type: token.IDENT, Literal: "anotherVar"},
-					Value: "anotherVar",
+			&ExpressionStatement{
+				Token: token.Token{Type: token.IDENT, Literal: "myVar"},
+				Expression: &BindExpression{
+					Token: token.Token{Type: token.BIND, Literal: ":="},
+					Left: &Identifier{
+						Token: token.Token{Type: token.IDENT, Literal: "myVar"},
+						Value: "myVar",
+					},
+					Value: &Identifier{
+						Token: token.Token{Type: token.IDENT, Literal: "anotherVar"},
+						Value: "anotherVar",
+					},
 				},
 			},
 		},
 	}
 
-	if program.String() != "let myVar = anotherVar;" {
-		t.Errorf("program.String wrong. got=%q", program.String())
-	}
+	assert.Equal(t, "myVar:=anotherVar", program.String())
 }