2 files changed, 128 insertions, 0 deletions
diff --git a/ast/ast.go b/ast/ast.go
index 033005f..619cb9f 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -1,11 +1,14 @@
 package ast
 
 import (
+	"bytes"
+
 	"github.com/mewsen/interpreter/token"
 )
 
 type Node interface {
 	TokenLiteral() string
+	String() string
 }
 
 type Statement interface {
@@ -30,6 +33,16 @@ 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 LetStatement struct {
 	Token token.Token
 	Name  *Identifier
@@ -38,6 +51,19 @@ type LetStatement struct {
 
 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())
+	}
+
+	return out.String()
+}
 
 type Identifier struct {
 	Token token.Token
@@ -46,3 +72,68 @@ type Identifier struct {
 
 func (i *Identifier) expressionNode()      {}
 func (i *Identifier) TokenLiteral() string { return i.Token.Literal }
+func (i *Identifier) String() string       { return i.Value }
+
+type ReturnStatement struct {
+	Token       token.Token
+	ReturnValue Expression
+}
+
+func (rs *ReturnStatement) statementNode()       {}
+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()
+}
+
+type ExpressionStatement struct {
+	Token      token.Token
+	Expression Expression
+}
+
+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 ""
+}
+
+type IntegerLiteral struct {
+	Token token.Token
+	Value int64
+}
+
+func (il *IntegerLiteral) expressionNode()      {}
+func (il *IntegerLiteral) TokenLiteral() string { return il.Token.Literal }
+func (il *IntegerLiteral) String() string       { return il.Token.Literal }
+
+type PrefixExpression struct {
+	Token    token.Token
+	Operator string
+	Right    Expression
+}
+
+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()
+}
diff --git a/ast/ast_test.go b/ast/ast_test.go
new file mode 100644
index 0000000..887827b
--- /dev/null
+++ b/ast/ast_test.go
@@ -0,0 +1,37 @@
+package ast
+
+import (
+	"testing"
+
+	"github.com/mewsen/interpreter/token"
+)
+
+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())
+	}
+}