waiig15/ast/ast.go

package ast

import (
	"bytes"
)

// Node is the interface implemented by every node in the AST. It extends the
// fmt.Stringer interface, allowing simple printing of nodes.
type Node interface {
	// TokenLiteral returns the literal value of the token it's associated to.
	TokenLiteral() string
	String() string
}

// Statement extends Node and is only a way to differentiate between expressions
// and statements.
type Statement interface {
	Node
	statementNode()
}

// Expression extends Node and is only a way to differentiate between
// expressions and statements.
type Expression interface {
	// Expression extends Node.
	Node
	expressionNode()
}

// Program represents the outer structure of the parser program.
type Program struct {
	Statements []Statement
}

// String satisfies the Node and fmt.Stringer interfaces.
func (p *Program) String() string {
	var out bytes.Buffer

	for _, s := range p.Statements {
		out.WriteString(s.String())
	}

	return out.String()
}

// TokenLiteral returns the string contents of the first statement token, which
// can be an empty string if the program is empty.
func (p *Program) TokenLiteral() string {
	if len(p.Statements) > 0 {
		return p.Statements[0].TokenLiteral()
	}

	return ""
}