prefix parsing

ast/ast.go

@@ -1,9 +1,13 @@
 package ast
 
-import "monkey/token"
+import (
+	"bytes"
+	"monkey/token"
+)
 
 type Node interface {
 	TokenLiteral() string
+	String() string
 }
 
 type Statement interface {
@@ -28,6 +32,16 @@ func (p *Program) TokenLiteral() string {
 	}
 }
 
+func (p *Program) String() string {
+	var out bytes.Buffer
+
+	for _, s := range p.Statements {
+		out.WriteString(s.String())
+	}
+
+	return out.String()
+}
+
 type Identifier struct {
 	Token token.Token // the token.Ident token
 	Value string
@@ -44,20 +58,102 @@ type ReturnStatement struct {
 	ReturnValue Expression
 }
 
+type ExpressionStatement struct {
+	Token      token.Token // the first token of the expression
+	Expression Expression
+}
+
+type IntegerLiteral struct {
+	Token token.Token
+	Value int64
+}
+
+type PrefixExpression struct {
+	Token    token.Token
+	Operator string
+	Right    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()
+}
 
 func (i *Identifier) expressionNode() {
 }
 func (i *Identifier) TokenLiteral() string {
 	return i.Token.Literal
 }
+func (i *Identifier) String() string { return i.Value }
 
-func (i *ReturnStatement) statementNode() {
+func (rs *ReturnStatement) statementNode() {
 }
-func (i *ReturnStatement) TokenLiteral() string {
-	return i.Token.Literal
+func (rs *ReturnStatement) TokenLiteral() string {
+	return rs.Token.Literal
+}
+func (rs *ReturnStatement) String() string {
+	var out bytes.Buffer
+
+	out.WriteString(rs.TokenLiteral() + " ")
+
+	if rs.ReturnValue != nil {
+		out.WriteString(rs.ReturnValue.String())
+	}
+
+	out.WriteString(";")
+
+	return out.String()
+}
+
+func (es *ExpressionStatement) statementNode() {
+}
+func (es *ExpressionStatement) TokenLiteral() string {
+	return es.Token.Literal
+}
+func (es *ExpressionStatement) String() string {
+	if es.Expression != nil {
+		return es.Expression.String()
+	}
+
+	return ""
+}
+
+func (il *IntegerLiteral) expressionNode() {
+}
+func (il *IntegerLiteral) TokenLiteral() string {
+	return il.Token.Literal
+}
+func (il *IntegerLiteral) String() string {
+	return il.Token.Literal
+}
+
+func (pe *PrefixExpression) expressionNode() {}
+func (pe *PrefixExpression) TokenLiteral() string {
+	return pe.Token.Literal
+}
+func (pe *PrefixExpression) String() string {
+	var out bytes.Buffer
+
+	out.WriteString("(")
+	out.WriteString(pe.Operator)
+	out.WriteString(pe.Right.String())
+	out.WriteString(")")
+
+	return out.String()
 }

ast/ast_test.go

@@ -0,0 +1,28 @@
+package ast
+
+import (
+	"monkey/token"
+	"testing"
+)
+
+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",
+				},
+			},
+		},
+	}
+
+	if program.String() != "let myVar = anotherVar;" {
+		t.Errorf("program.String wrong. got=%q", program.String())
+	}
+}