2 files changed, 83 insertions, 1 deletions

diff --git a/ast/ast.go b/ast/ast.go
index c53dfdf..fea8b60 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -1,9 +1,13 @@
 package ast
 
-import "mana/tokens"
+import (
+	"bytes"
+	"mana/tokens"
+)
 
 type Node interface {
 	TokenLiteral() string
+	String() string
 }
 
 type Statement interface {
@@ -30,6 +34,19 @@ func (p *Program) TokenLiteral() string {
 	return ""
 }
 
+// String returns a string representation of the program. This is used only for
+// debugging and testing.
+
+func (p *Program) String() string {
+	var out bytes.Buffer
+
+	for _, s := range p.Statements {
+		out.WriteString(s.String())
+	}
+
+	return out.String()
+}
+
 // LetStatement represents a let statement.
 type LetStatement struct {
 	Token tokens.Token // the token.LET token
@@ -41,6 +58,21 @@ 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()
+}
 
 // Identifier represents an identifier.
 type Identifier struct {
@@ -52,6 +84,9 @@ func (i *Identifier) expressionNode() {}
 func (i *Identifier) TokenLiteral() string {
 	return i.Token.Literal
 }
+func (i *Identifier) String() string {
+	return i.Value
+}
 
 // ReturnStatement represents a return statement.
 type ReturnStatement struct {
@@ -63,6 +98,19 @@ 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()
+}
 
 // ExpressionStatement represents an expression statement.
 type ExpressionStatement struct {
@@ -74,3 +122,9 @@ 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 ""
+}
diff --git a/ast/ast_test.go b/ast/ast_test.go
new file mode 100644
index 0000000..e16cc11
--- /dev/null
+++ b/ast/ast_test.go
@@ -0,0 +1,28 @@
+package ast
+
+import (
+	"mana/tokens"
+	"testing"
+)
+
+func TestString(t *testing.T) {
+	var program = &Program{
+		Statements: []Statement{
+			&LetStatement{
+				Token: tokens.Token{Type: tokens.LET, Literal: "let"},
+				Name: &Identifier{
+					Token: tokens.Token{Type: tokens.IDENT, Literal: "myVar"},
+					Value: "myVar",
+				},
+				Value: &Identifier{
+					Token: tokens.Token{Type: tokens.IDENT, Literal: "anotherVar"},
+					Value: "anotherVar",
+				},
+			},
+		},
+	}
+
+	if program.String() != "let myVar = anotherVar;" {
+		t.Errorf("program.String() wrong. got=%q", program.String())
+	}
+}