forked from hashicorp/terraform
/
expr_lex.go
134 lines (114 loc) · 2.2 KB
/
expr_lex.go
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package config
import (
"bytes"
"fmt"
"log"
"unicode"
"unicode/utf8"
)
// The parser expects the lexer to return 0 on EOF.
const lexEOF = 0
// The parser uses the type <prefix>Lex as a lexer. It must provide
// the methods Lex(*<prefix>SymType) int and Error(string).
type exprLex struct {
Err error
Input string
pos int
width int
}
// The parser calls this method to get each new token.
func (x *exprLex) Lex(yylval *exprSymType) int {
for {
c := x.next()
if c == lexEOF {
return lexEOF
}
// Ignore all whitespace
if unicode.IsSpace(c) {
continue
}
switch c {
case '"':
return x.lexString(yylval)
case ',':
return COMMA
case '(':
return LEFTPAREN
case ')':
return RIGHTPAREN
default:
x.backup()
return x.lexId(yylval)
}
}
}
func (x *exprLex) lexId(yylval *exprSymType) int {
var b bytes.Buffer
for {
c := x.next()
if c == lexEOF {
break
}
// If this isn't a character we want in an ID, return out.
// One day we should make this a regexp.
if c != '_' &&
c != '-' &&
c != '.' &&
c != '*' &&
!unicode.IsLetter(c) &&
!unicode.IsNumber(c) {
x.backup()
break
}
if _, err := b.WriteRune(c); err != nil {
log.Printf("ERR: %s", err)
return lexEOF
}
}
yylval.str = b.String()
return IDENTIFIER
}
func (x *exprLex) lexString(yylval *exprSymType) int {
var b bytes.Buffer
for {
c := x.next()
if c == lexEOF {
break
}
// String end
if c == '"' {
break
}
if _, err := b.WriteRune(c); err != nil {
log.Printf("ERR: %s", err)
return lexEOF
}
}
yylval.str = b.String()
return STRING
}
// Return the next rune for the lexer.
func (x *exprLex) next() rune {
if int(x.pos) >= len(x.Input) {
x.width = 0
return lexEOF
}
r, w := utf8.DecodeRuneInString(x.Input[x.pos:])
x.width = w
x.pos += x.width
return r
}
// peek returns but does not consume the next rune in the input
func (x *exprLex) peek() rune {
r := x.next()
x.backup()
return r
}
// backup steps back one rune. Can only be called once per next.
func (x *exprLex) backup() {
x.pos -= x.width
}
// The parser calls this method on a parse error.
func (x *exprLex) Error(s string) {
x.Err = fmt.Errorf("parse error: %s", s)
}