func list1() (*ast.ListCell, *ast.ListCell) {
l0 := ast.NewList()
l0.Add(ast.NewSym("+"))
l0.Add(ast.NewSym("x"))
l1 := l0.Add(ast.NewList()).(*ast.ListCell)
l1.Add(ast.NewSym("*"))
l1.Add(ast.NewNum(4))
l1.Add(ast.NewNum(7))
l0.Add(ast.NewNum(1))
return l0, l1
}
func list2() (*ast.ListCell,
*ast.ListCell,
*ast.ListCell,
*ast.ListCell,
*ast.ListCell) {
// l0 is the top list, l1 and l2 are elements of l0
// l3 and l4 are elements of l2
l0 := ast.NewList()
l0.Add(ast.NewNum(3))
l1 := l0.Add(ast.NewList()).(*ast.ListCell)
l2 := l0.Add(ast.NewList()).(*ast.ListCell)
l3 := l2.Add(ast.NewList()).(*ast.ListCell)
l2.Add(ast.NewSym("g"))
l4 := l2.Add(ast.NewList()).(*ast.ListCell)
return l0, l1, l2, l3, l4
}
func (p *Parser) parseQuote(t token.Item) (ast.Cell, error) {
qList := ast.NewList()
qCell, err1 := ast.NewSym("quote")
val, err2 := p.parseAST(<-p.tokens)
if err1 != nil {
return nil, err1
}
if err2 != nil {
return nil, err2
}
qList.Add(qCell)
qList.Add(val)
return qList, nil
}
func (p *Parser) parseAST(t token.Item) (ast.Cell, error) {
var val ast.Cell
var err error
switch t.Type {
// use following tokens to recursivly build the tree
case token.LParen:
val, err = p.parseTree(ast.NewList())
// this "tree" is a single sym
case token.Sym:
val, err = ast.NewSym(t.Value)
// this "tree" is a single constant
case token.Const:
val, err = p.parseConst(t)
// the next token is quoted
case token.Quote:
val, err = p.parseQuote(t)
// close paren found without open paren, error
case token.RParen:
val, err = nil, errors.New("syntax error: close parenthese ')' without s-expression")
case token.EOF:
val, err = ast.NewEOF(), nil
}
return val, err
}