waiig15/ast/ast.go

package ast

import (
	"bytes"

	"code.osinet.fr/fgm/waiig15/token"
)

// 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
}

// 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 ""
}

// 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()
}

// LetStatement is the Node type for Let statements.
type LetStatement struct {
	Token token.Token // the token.LET token. Why do we need it ?
	Name  *Identifier
	Value Expression
}

func (ls *LetStatement) statementNode() {}

// TokenLiteral satisfies the Node interface.
func (ls *LetStatement) TokenLiteral() string {
	return ls.Token.Literal
}

// String implements Node and fmt.Stringer.
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()
}

// ReturnStatement fulfills the Node and Statement interfaces.
type ReturnStatement struct {
	Token       token.Token // the token.RETURN token. Why do we need it ?
	Name        *Identifier
	ReturnValue Expression
}

func (rs *ReturnStatement) statementNode() {}

// TokenLiteral satisfies the Node interface.
func (rs *ReturnStatement) TokenLiteral() string {
	return rs.Token.Literal
}

// String satisfies the Node and fmt.Stringer interfaces.
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 fulfills the Node and Statement interfaces.
// It represents a statement made of a bare expression like:
//   x + 10;
type ExpressionStatement struct {
	Token      token.Token // the first token of the expression
	Expression Expression
}

func (es *ExpressionStatement) statementNode() {}

// TokenLiteral satisfies the Node interface.
func (es *ExpressionStatement) TokenLiteral() string {
	return es.Token.Literal
}

// String satisfies the Node and fmt.Stringer interfaces.
func (es *ExpressionStatement) String() string {
	if es.Expression != nil {
		return es.Expression.String()
	}
	return ""
}

// Identifier is the Node type for identifiers.
type Identifier struct {
	Token token.Token // the token.IDENT token. Why do we need it ?
	Value string      // The identifier string.
}

func (i *Identifier) expressionNode() {}

// TokenLiteral satisfies the Node interface.
func (i *Identifier) TokenLiteral() string {
	return i.Token.Literal
}

func (i *Identifier) String() string {
	return i.Value
}

// IntegerLiteral fulfills ast.Expression.
type IntegerLiteral struct {
	Token token.Token
	Value int64
}

func (il *IntegerLiteral) expressionNode() {}

// TokenLiteral satisfies the Node interface.
func (il *IntegerLiteral) TokenLiteral() string {
	return il.Token.Literal
}
func (il *IntegerLiteral) String() string {
	return il.Token.Literal
}

// PrefixExpression fulfills the Node and Statement interfaces.
// It represents a prefixed expression like:
// "-5;"
type PrefixExpression struct {
	Token    token.Token // The prefix token, e.g. !
	Operator string
	Right    Expression
}

func (pe *PrefixExpression) expressionNode() {}

// TokenLiteral satisfies the Node interface.
func (pe *PrefixExpression) TokenLiteral() string {
	return pe.Token.Literal
}

// String satisfies the Node and fmt.Stringer interfaces.
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()
}

// InfixExpression fulfills the Node and Statement interfaces.
// It represents a prefixed expression like:
// "-5;"
type InfixExpression struct {
	Token    token.Token // The operator token, e.g. +
	Left     Expression
	Operator string
	Right    Expression
}

func (ie *InfixExpression) expressionNode() {}

// TokenLiteral satisfies the Node interface.
func (ie *InfixExpression) TokenLiteral() string {
	return ie.Token.Literal
}

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

	out.WriteString("(")
	out.WriteString(ie.Left.String())
	out.WriteString(" " + ie.Operator + " ")
	out.WriteString(ie.Right.String())
	out.WriteString(")")

	return out.String()
}