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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package regexp implements a simple regular expression library.
//
// The syntax of the regular expressions accepted is:
//
// regexp:
// concatenation { '|' concatenation }
// concatenation:
// { closure }
// closure:
// term [ '*' | '+' | '?' ]
// term:
// '^'
// '$'
// '.'
// character
// '[' [ '^' ] character-ranges ']'
// '(' regexp ')'
//
"bytes"
"container/vector"
"io"
"os"
"strings"
"utf8"
ErrInternal = os.NewError("internal error")
ErrUnmatchedLpar = os.NewError("unmatched '('")
ErrUnmatchedRpar = os.NewError("unmatched ')'")
ErrUnmatchedLbkt = os.NewError("unmatched '['")
ErrUnmatchedRbkt = os.NewError("unmatched ']'")
ErrBadRange = os.NewError("bad range in character class")
ErrExtraneousBackslash = os.NewError("extraneous backslash")
ErrBadClosure = os.NewError("repeated closure (**, ++, etc.)")
ErrBareClosure = os.NewError("closure applies to nothing")
ErrBadBackslash = os.NewError("illegal backslash escape")
// An instruction executed by the NFA
kind() int // the type of this instruction: _CHAR, _ANY, etc.
next() instr // the instruction to execute after this one
setNext(i instr)
index() int
setIndex(i int)
print()
// Fields and methods common to all instructions
_next instr
_index int
func (c *common) next() instr { return c._next }
func (c *common) setNext(i instr) { c._next = i }
func (c *common) index() int { return c._index }
func (c *common) setIndex(i int) { c._index = i }
// Regexp is the representation of a compiled regular expression.
// The public interface is entirely through methods.
type Regexp struct {
expr string // the original expression
prefix string // initial plain text string
prefixBytes []byte // initial plain text bytes
inst *vector.Vector
start instr // first instruction of machine
prefixStart instr // where to start if there is a prefix
nbra int // number of brackets in expression, for subexpressions
_START = iota // beginning of program
_END // end of program: success
_BOT // '^' beginning of text
_EOT // '$' end of text
_CHAR // 'a' regular character
_CHARCLASS // [a-z] character class
_ANY // '.' any character including newline
_NOTNL // [^\n] special case: any character but newline
_BRA // '(' parenthesized expression
_EBRA // ')'; end of '(' parenthesized expression
_ALT // '|' alternation
_NOP // do nothing; makes it easy to link without patching
)
// --- START start of program
type _Start struct {
func (start *_Start) kind() int { return _START }
func (start *_Start) print() { print("start") }
type _End struct {
func (end *_End) kind() int { return _END }
func (end *_End) print() { print("end") }
type _Bot struct {
func (bot *_Bot) kind() int { return _BOT }
func (bot *_Bot) print() { print("bot") }
type _Eot struct {
func (eot *_Eot) kind() int { return _EOT }
func (eot *_Eot) print() { print("eot") }
// --- CHAR a regular character
type _Char struct {
func (char *_Char) kind() int { return _CHAR }
func (char *_Char) print() { print("char ", string(char.char)) }
func newChar(char int) *_Char {
c := new(_Char)
c.char = char
return c
type _CharClass struct {
common
char int
negate bool // is character class negated? ([^a-z])
// vector of int, stored pairwise: [a-z] is (a,z); x is (x,x):
ranges *vector.IntVector
func (cclass *_CharClass) kind() int { return _CHARCLASS }
print(" (negated)")
l := cclass.ranges.At(i)
r := cclass.ranges.At(i + 1)
print(" [", string(l), "]")
print(" [", string(l), "-", string(r), "]")
func (cclass *_CharClass) addRange(a, b int) {
cclass.ranges.Push(a)
cclass.ranges.Push(b)
func (cclass *_CharClass) matches(c int) bool {
for i := 0; i < cclass.ranges.Len(); i = i + 2 {
min := cclass.ranges.At(i)
max := cclass.ranges.At(i + 1)
return !cclass.negate
func newCharClass() *_CharClass {
c := new(_CharClass)
c.ranges = new(vector.IntVector)
return c
type _Any struct {
func (any *_Any) kind() int { return _ANY }
func (any *_Any) print() { print("any") }
// --- NOTNL any character but newline
type _NotNl struct {
func (notnl *_NotNl) kind() int { return _NOTNL }
func (notnl *_NotNl) print() { print("notnl") }
// --- BRA parenthesized expression
type _Bra struct {
common
n int // subexpression number
func (bra *_Bra) kind() int { return _BRA }
func (bra *_Bra) print() { print("bra", bra.n) }
// --- EBRA end of parenthesized expression
type _Ebra struct {
common
n int // subexpression number
func (ebra *_Ebra) kind() int { return _EBRA }
func (ebra *_Ebra) print() { print("ebra ", ebra.n) }
type _Alt struct {
common
left instr // other branch
func (alt *_Alt) kind() int { return _ALT }
func (alt *_Alt) print() { print("alt(", alt.left.index(), ")") }
type _Nop struct {
func (nop *_Nop) kind() int { return _NOP }
func (nop *_Nop) print() { print("nop") }
func (re *Regexp) add(i instr) instr {
i.setIndex(re.inst.Len())
re.inst.Push(i)
return i
re *Regexp
error os.Error
nlpar int // number of unclosed lpars
pos int
ch int
func (p *parser) c() int { return p.ch }
p.ch = endOfFile
c, w := utf8.DecodeRuneInString(p.re.expr[p.pos:])
p.ch = c
p.pos += w
p := new(parser)
p.re = re
p.nextc() // load p.ch
return p
}
func special(c int) bool {
return true
return true
cc.negate = true
p.nextc()
p.error = ErrBadRange
return nil
// Is it [^\n]?
if cc.negate && cc.ranges.Len() == 2 &&
cc.ranges.At(0) == '\n' && cc.ranges.At(1) == '\n' {
nl := new(_NotNl)
p.re.add(nl)
return nl
// Special common case: "[a]" -> "a"
if !cc.negate && cc.ranges.Len() == 2 && cc.ranges.At(0) == cc.ranges.At(1) {
c := newChar(cc.ranges.At(0))
p.re.add(c)
return c
p.re.add(cc)
return cc
case '-': // do this before backslash processing
p.error = ErrBadRange
return nil
p.error = ErrExtraneousBackslash
return nil
c = '\n'
case specialcclass(c):
// c is as delivered
default:
p.error = ErrBadBackslash
return nil
case left < 0: // first of pair
if p.c() == '-' { // range
p.nextc()
left = c
} else { // single char
cc.addRange(c, c)
case left <= c: // second of pair
cc.addRange(left, c)
left = -1
p.error = ErrBadRange
return nil
func (p *parser) term() (start, end instr) {
// term() is the leaf of the recursion, so it's sufficient to pick off the
// error state here for early exit.
// The other functions (closure(), concatenation() etc.) assume
// it's safe to recur to here.
if p.error != nil {
return
return nil, nil
p.error = ErrBareClosure
return
p.error = ErrUnmatchedRpar
return
p.error = ErrUnmatchedRbkt
return
p.nextc()
start = p.re.add(new(_Bot))
return start, start
p.nextc()
start = p.re.add(new(_Eot))
return start, start
p.nextc()
start = p.re.add(new(_Any))
return start, start
p.nextc()
start = p.charClass()
return
p.error = ErrUnmatchedLbkt
return
p.nextc()
return start, start
p.nextc()
p.nlpar++
p.re.nbra++ // increment first so first subexpr is \1
nbra := p.re.nbra
start, end = p.regexp()
p.error = ErrUnmatchedLpar
return
p.nlpar--
p.nextc()
bra := new(_Bra)
p.re.add(bra)
ebra := new(_Ebra)
p.re.add(ebra)
bra.n = nbra
ebra.n = nbra
if start == nil {
if end == nil {
p.error = ErrInternal
return
end.setNext(ebra)
bra.setNext(start)
return bra, ebra
p.error = ErrExtraneousBackslash
return
c = '\n'
case special(c):
// c is as delivered
default:
p.error = ErrBadBackslash
return
p.nextc()
start = newChar(c)
p.re.add(start)
return start, start
func (p *parser) closure() (start, end instr) {
if start == nil || p.error != nil {
return
}
switch p.c() {
case '*':
// (start,end)*:
alt := new(_Alt)
p.re.add(alt)
end.setNext(alt) // after end, do alt
alt.left = start // alternate brach: return to start
start = alt // alt becomes new (start, end)
end = alt
alt := new(_Alt)
p.re.add(alt)
end.setNext(alt) // after end, do alt
alt.left = start // alternate brach: return to start
end = alt // start is unchanged; end is alt
alt := new(_Alt)
p.re.add(alt)
nop := new(_Nop)
p.re.add(nop)
alt.left = start // alternate branch is start
alt.setNext(nop) // follow on to nop
end.setNext(nop) // after end, go to nop
start = alt // start is now alt
end = nop // end is nop pointed to by both branches
return
}
switch p.nextc() {
case '*', '+', '?':
p.error = ErrBadClosure
func (p *parser) concatenation() (start, end instr) {
nstart, nend := p.closure()
return
case nstart == nil: // end of this concatenation
if start == nil { // this is the empty string
nop := p.re.add(new(_Nop))
return nop, nop
return
case start == nil: // this is first element of concatenation
start, end = nstart, nend
end.setNext(nstart)
end = nend
func (p *parser) regexp() (start, end instr) {
start, end = p.concatenation()
return
for {
switch p.c() {
default:
return
p.nextc()
nstart, nend := p.concatenation()
return
alt := new(_Alt)
p.re.add(alt)
alt.left = start
alt.setNext(nstart)
nop := new(_Nop)
p.re.add(nop)
end.setNext(nop)
nend.setNext(nop)
start, end = alt, nop
func unNop(i instr) instr {
i = i.next()
inst := re.inst.At(i).(instr)
continue
inst.setNext(unNop(inst.next()))
alt := inst.(*_Alt)
alt.left = unNop(alt.left)
print("prefix <", re.prefix, ">\n")
inst := re.inst.At(i).(instr)
print(inst.index(), ": ")
inst.print()
print(" -> ", inst.next().index())
func (re *Regexp) doParse() os.Error {
p := newParser(re)
start := new(_Start)
re.add(start)
s, e := p.regexp()
return p.error
start.setNext(s)
re.start = start
e.setNext(re.add(new(_End)))
// Extract regular text from the beginning of the pattern.
// That text can be used by doExecute to speed up matching.
var b []byte
var utf = make([]byte, utf8.UTFMax)
i := re.inst.At(0).(instr).next().index()
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Loop:
inst := re.inst.At(i).(instr)
// stop if this is not a char
if inst.kind() != _CHAR {
break
}
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// stop if this char can be followed by a match for an empty string,
// which includes closures, ^, and $.
switch re.inst.At(inst.next().index()).(instr).kind() {
case _BOT, _EOT, _ALT:
break Loop
n := utf8.EncodeRune(inst.(*_Char).char, utf)
b = bytes.Add(b, utf[0:n])
i = inst.next().index()
// point prefixStart instruction to first non-CHAR after prefix
re.prefixStart = re.inst.At(i).(instr)
re.prefixBytes = b
re.prefix = string(b)
// Compile parses a regular expression and returns, if successful, a Regexp
// object that can be used to match against text.
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func Compile(str string) (regexp *Regexp, error os.Error) {
regexp = new(Regexp)
regexp.expr = str
regexp.inst = new(vector.Vector)
error = regexp.doParse()
return
}
// MustCompile is like Compile but panics if the expression cannot be parsed.
// It simplifies safe initialization of global variables holding compiled regular
// expressions.
func MustCompile(str string) *Regexp {
regexp, error := Compile(str)
panicln(`regexp: compiling "`, str, `": `, error.String())
// NumSubexp returns the number of parenthesized subexpressions in this Regexp.
func (re *Regexp) NumSubexp() int { return re.nbra }
// The match arena allows us to reduce the garbage generated by tossing
// match vectors away as we execute. Matches are ref counted and returned
// to a free list when no longer active. Increases a simple benchmark by 22X.
type matchArena struct {
head *matchVec
len int // length of match vector
}
type matchVec struct {
m []int // pairs of bracketing submatches. 0th is start,end
ref int
next *matchVec
}
func (a *matchArena) new() *matchVec {
if a.head == nil {
const N = 10
block := make([]matchVec, N)
for i := 0; i < N; i++ {
b := &block[i]
b.next = a.head
a.head = b
m := a.head
a.head = m.next
m.ref = 0
if m.m == nil {
m.m = make([]int, a.len)
}
}
func (a *matchArena) free(m *matchVec) {
m.next = a.head
a.head = m
}
}
func (a *matchArena) copy(m *matchVec) *matchVec {
m1 := a.new()
copy(m1.m, m.m)
return m1
}
func (a *matchArena) noMatch() *matchVec {
for i := range m.m {
m.m[i] = -1 // no match seen; catches cases like "a(b)?c" on "ac"
inst instr // next instruction to execute
match *matchVec
}
// Append new state to to-do list. Leftmost-longest wins so avoid
// adding a state that's already active. The matchVec will be inc-ref'ed
// if it is assigned to a state.
func (a *matchArena) addState(s []state, inst instr, match *matchVec, pos, end int) []state {
switch inst.kind() {
case _BOT:
if pos == 0 {
s = a.addState(s, inst.next(), match, pos, end)
case _EOT:
if pos == end {
s = a.addState(s, inst.next(), match, pos, end)
case _BRA:
n := inst.(*_Bra).n
match.m[2*n] = pos
s = a.addState(s, inst.next(), match, pos, end)
return s
case _EBRA:
n := inst.(*_Ebra).n
match.m[2*n+1] = pos
s = a.addState(s, inst.next(), match, pos, end)
return s
index := inst.index()
l := len(s)
// States are inserted in order so it's sufficient to see if we have the same
// instruction; no need to see if existing match is earlier (it is).
if s[i].inst.index() == index {
return s
s1 := make([]state, 2*l)[0:l]
copy(s1, s)
s = s1
s = s[0 : l+1]
s[l].inst = inst
s[l].match = match
match.ref++
if inst.kind() == _ALT {
s = a.addState(s, inst.(*_Alt).left, a.copy(match), pos, end)
// give other branch a copy of this match vector
s = a.addState(s, inst.next(), a.copy(match), pos, end)
// Accepts either string or bytes - the logic is identical either way.
// If bytes == nil, scan str.
func (re *Regexp) doExecute(str string, bytestr []byte, pos int) []int {
var s [2][]state
s[0] = make([]state, 10)[0:0]
s[1] = make([]state, 10)[0:0]
in, out := 0, 1
var final state
found := false
end := len(str)
if bytestr != nil {
end = len(bytestr)
}
// fast check for initial plain substring
prefixed := false // has this iteration begun by skipping a prefix?
advance = strings.Index(str[pos:], re.prefix)
advance = bytes.Index(bytestr[pos:], re.prefixBytes)
}
if advance == -1 {
return []int{}
}
pos += advance + len(re.prefix)
arena := &matchArena{nil, 2 * (re.nbra + 1)}
for pos <= end {
if !found {
// prime the pump if we haven't seen a match yet
match := arena.noMatch()
match.m[0] = pos
if prefixed {
s[out] = arena.addState(s[out], re.prefixStart, match, pos, end)
prefixed = false // next iteration should start at beginning of machine.
} else {
s[out] = arena.addState(s[out], re.start.next(), match, pos, end)
}
arena.free(match) // if addState saved it, ref was incremented
in, out = out, in // old out state is new in state
// clear out old state
for _, state := range old {
arena.free(state.match)
}
s[out] = old[0:0] // truncate state vector
if found && len(s[in]) == 0 {
charwidth := 1
c := endOfFile
if pos < end {
c, charwidth = utf8.DecodeRuneInString(str[pos:end])
} else {
c, charwidth = utf8.DecodeRune(bytestr[pos:end])
for _, st := range s[in] {
switch st.inst.kind() {
case _BOT:
case _EOT:
case _CHAR:
if c == st.inst.(*_Char).char {
s[out] = arena.addState(s[out], st.inst.next(), st.match, pos, end)
case _CHARCLASS:
s[out] = arena.addState(s[out], st.inst.next(), st.match, pos, end)
s[out] = arena.addState(s[out], st.inst.next(), st.match, pos, end)
case _NOTNL:
if c != endOfFile && c != '\n' {
s[out] = arena.addState(s[out], st.inst.next(), st.match, pos, end)
case _BRA:
case _EBRA:
case _ALT:
case _END:
if !found || // first
st.match.m[0] < final.match.m[0] || // leftmost
(st.match.m[0] == final.match.m[0] && pos-charwidth > final.match.m[1]) { // longest
if final.match != nil {
arena.free(final.match)
}
final = st
final.match.ref++
final.match.m[1] = pos - charwidth
st.inst.print()
panic("unknown instruction in execute")
if final.match == nil {
return nil
}
// if match found, back up start of match by width of prefix.
if re.prefix != "" && len(final.match.m) > 0 {
final.match.m[0] -= len(re.prefix)
// ExecuteString matches the Regexp against the string s.
// The return value is an array of integers, in pairs, identifying the positions of
// substrings matched by the expression.
// s[a[0]:a[1]] is the substring matched by the entire expression.
// s[a[2*i]:a[2*i+1]] for i > 0 is the substring matched by the ith parenthesized subexpression.
// A negative value means the subexpression did not match any element of the string.
func (re *Regexp) ExecuteString(s string) (a []int) {
return re.doExecute(s, nil, 0)
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// Execute matches the Regexp against the byte slice b.
// The return value is an array of integers, in pairs, identifying the positions of
// subslices matched by the expression.
// b[a[0]:a[1]] is the subslice matched by the entire expression.
// b[a[2*i]:a[2*i+1]] for i > 0 is the subslice matched by the ith parenthesized subexpression.
// A negative value means the subexpression did not match any element of the slice.
// An empty array means "no match".
func (re *Regexp) Execute(b []byte) (a []int) { return re.doExecute("", b, 0) }
// MatchString returns whether the Regexp matches the string s.
// The return value is a boolean: true for match, false for no match.
func (re *Regexp) MatchString(s string) bool { return len(re.doExecute(s, nil, 0)) > 0 }
// Match returns whether the Regexp matches the byte slice b.
// The return value is a boolean: true for match, false for no match.
func (re *Regexp) Match(b []byte) bool { return len(re.doExecute("", b, 0)) > 0 }
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// MatchStrings matches the Regexp against the string s.
// The return value is an array of strings matched by the expression.
// a[0] is the substring matched by the entire expression.
// a[i] for i > 0 is the substring matched by the ith parenthesized subexpression.
// An empty array means ``no match''.
func (re *Regexp) MatchStrings(s string) (a []string) {
r := re.doExecute(s, nil, 0)
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if r == nil {
return nil
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}
a = make([]string, len(r)/2)
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for i := 0; i < len(r); i += 2 {
if r[i] != -1 { // -1 means no match for this subexpression
a[i/2] = s[r[i]:r[i+1]]
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}
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}
// MatchSlices matches the Regexp against the byte slice b.
// The return value is an array of subslices matched by the expression.
// a[0] is the subslice matched by the entire expression.
// a[i] for i > 0 is the subslice matched by the ith parenthesized subexpression.
// An empty array means ``no match''.
func (re *Regexp) MatchSlices(b []byte) (a [][]byte) {
r := re.doExecute("", b, 0)
if r == nil {
return nil
a = make([][]byte, len(r)/2)
for i := 0; i < len(r); i += 2 {
if r[i] != -1 { // -1 means no match for this subexpression
a[i/2] = b[r[i]:r[i+1]]
}
// MatchString checks whether a textual regular expression
// matches a string. More complicated queries need
// to use Compile and the full Regexp interface.
func MatchString(pattern string, s string) (matched bool, error os.Error) {
re, err := Compile(pattern)
if err != nil {
return false, err
return re.MatchString(s), nil
// Match checks whether a textual regular expression
// matches a byte slice. More complicated queries need
// to use Compile and the full Regexp interface.
func Match(pattern string, b []byte) (matched bool, error os.Error) {
re, err := Compile(pattern)
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if err != nil {
return false, err