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114 lines
2.2 KiB
Go

package main
import (
"fmt"
"io"
)
const ()
func parse(r io.Reader) (node, error) {
p := &parser{
root: newRootNode(),
input: lex(r),
backup: make([]token, 0, 8),
}
if err := p.parse(); err != nil {
return nil, err
}
return p.root, nil
}
type parser struct {
root node
input chan token
backup []token
}
func (p *parser) parse() error {
if p.root == nil {
p.root = newRootNode()
}
return p.root.parse(p)
}
// returns the next token and advances the input stream
func (p *parser) next() token {
if len(p.backup) > 0 {
t := p.backup[len(p.backup)-1]
p.backup = p.backup[:len(p.backup)-1]
return t
}
SKIP_COMMENTS:
t, ok := <-p.input
if !ok {
return token{t_eof, "eof"}
}
if t.t == t_comment {
goto SKIP_COMMENTS
}
return t
}
func (p *parser) peek() token {
t := p.next()
p.unread(t)
return t
}
func (p *parser) unread(t token) {
if p.backup == nil {
p.backup = make([]token, 0, 8)
}
p.backup = append(p.backup, t)
}
func (p *parser) ensureNext(tt tokenType, context string) error {
if p.peek().t != tt {
return fmt.Errorf("unexpected %v in %s: expected %v", p.peek().t, context, tt)
}
return nil
}
// parse the next value. This is to be executed in a context where we know we
// want something that is a value to come next, such as after an equals sign.
func (p *parser) parseValue() (node, error) {
for {
t := p.peek()
switch t.t {
case t_error:
return nil, fmt.Errorf("parse error: saw lex error when looking for value: %v", t.s)
case t_eof:
return nil, fmt.Errorf("parse error: unexpected eof when looking for value")
case t_string:
n := new(stringNode)
if err := n.parse(p); err != nil {
return nil, err
}
return n, nil
case t_real_number:
n := new(numberNode)
if err := n.parse(p); err != nil {
return nil, err
}
return n, nil
case t_list_start:
p.next()
n := new(listNode)
if err := n.parse(p); err != nil {
return nil, err
}
return n, nil
case t_object_start:
p.next()
n := &objectNode{}
if err := n.parse(p); err != nil {
return nil, err
}
return n, nil
default:
return nil, fmt.Errorf("parse error: unexpected %v token while looking for value", t.t)
}
}
}