// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-// Regular expression library.
-
+// 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 ')'
+//
package regexp
import (
var debug = false;
-
+// Error codes returned by faliures to parse an expression.
var ErrInternal = os.NewError("internal error");
var ErrUnmatchedLpar = os.NewError("unmatched '('");
var ErrUnmatchedRpar = os.NewError("unmatched ')'");
// An instruction executed by the NFA
type instr interface {
- Type() 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();
+ 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
type common struct {
- next instr;
- index int;
+ _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 }
+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 }
-type _RE struct {
+// The representation of a compiled regular expression.
+// The public interface is entirely through methods.
+type Regexp struct {
expr string; // the original expression
- ch chan<- *_RE; // reply channel when we're done
+ ch chan<- *Regexp; // reply channel when we're done
error *os.Error; // compile- or run-time error; nil if OK
inst *array.Array;
start instr;
common
}
-func (start *_Start) Type() int { return _START }
-func (start *_Start) Print() { print("start") }
+func (start *_Start) kind() int { return _START }
+func (start *_Start) print() { print("start") }
// --- END end of program
type _End struct {
common
}
-func (end *_End) Type() int { return _END }
-func (end *_End) Print() { print("end") }
+func (end *_End) kind() int { return _END }
+func (end *_End) print() { print("end") }
// --- BOT beginning of text
type _Bot struct {
common
}
-func (bot *_Bot) Type() int { return _BOT }
-func (bot *_Bot) Print() { print("bot") }
+func (bot *_Bot) kind() int { return _BOT }
+func (bot *_Bot) print() { print("bot") }
// --- EOT end of text
type _Eot struct {
common
}
-func (eot *_Eot) Type() int { return _EOT }
-func (eot *_Eot) Print() { print("eot") }
+func (eot *_Eot) kind() int { return _EOT }
+func (eot *_Eot) print() { print("eot") }
// --- CHAR a regular character
type _Char struct {
char int;
}
-func (char *_Char) Type() int { return _CHAR }
-func (char *_Char) Print() { print("char ", string(char.char)) }
+func (char *_Char) kind() int { return _CHAR }
+func (char *_Char) print() { print("char ", string(char.char)) }
func newChar(char int) *_Char {
c := new(_Char);
ranges *array.IntArray;
}
-func (cclass *_CharClass) Type() int { return _CHARCLASS }
+func (cclass *_CharClass) kind() int { return _CHARCLASS }
-func (cclass *_CharClass) Print() {
+func (cclass *_CharClass) print() {
print("charclass");
if cclass.negate {
print(" (negated)");
}
}
-func (cclass *_CharClass) AddRange(a, b int) {
+func (cclass *_CharClass) addRange(a, b int) {
// range is a through b inclusive
cclass.ranges.Push(a);
cclass.ranges.Push(b);
}
-func (cclass *_CharClass) Matches(c int) bool {
+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);
common
}
-func (any *_Any) Type() int { return _ANY }
-func (any *_Any) Print() { print("any") }
+func (any *_Any) kind() int { return _ANY }
+func (any *_Any) print() { print("any") }
// --- BRA parenthesized expression
type _Bra struct {
n int; // subexpression number
}
-func (bra *_Bra) Type() int { return _BRA }
-func (bra *_Bra) Print() { print("bra", bra.n); }
+func (bra *_Bra) kind() int { return _BRA }
+func (bra *_Bra) print() { print("bra", bra.n); }
// --- EBRA end of parenthesized expression
type _Ebra struct {
n int; // subexpression number
}
-func (ebra *_Ebra) Type() int { return _EBRA }
-func (ebra *_Ebra) Print() { print("ebra ", ebra.n); }
+func (ebra *_Ebra) kind() int { return _EBRA }
+func (ebra *_Ebra) print() { print("ebra ", ebra.n); }
// --- ALT alternation
type _Alt struct {
left instr; // other branch
}
-func (alt *_Alt) Type() int { return _ALT }
-func (alt *_Alt) Print() { print("alt(", alt.left.Index(), ")"); }
+func (alt *_Alt) kind() int { return _ALT }
+func (alt *_Alt) print() { print("alt(", alt.left.index(), ")"); }
// --- NOP no operation
type _Nop struct {
common
}
-func (nop *_Nop) Type() int { return _NOP }
-func (nop *_Nop) Print() { print("nop") }
+func (nop *_Nop) kind() int { return _NOP }
+func (nop *_Nop) print() { print("nop") }
// report error and exit compiling/executing goroutine
-func (re *_RE) Error(err *os.Error) {
+func (re *Regexp) setError(err *os.Error) {
re.error = err;
re.ch <- re;
sys.Goexit();
}
-func (re *_RE) Add(i instr) instr {
- i.SetIndex(re.inst.Len());
+func (re *Regexp) add(i instr) instr {
+ i.setIndex(re.inst.Len());
re.inst.Push(i);
return i;
}
type parser struct {
- re *_RE;
+ re *Regexp;
nlpar int; // number of unclosed lpars
pos int;
ch int;
return p.ch;
}
-func newParser(re *_RE) *parser {
+func newParser(re *Regexp) *parser {
p := new(parser);
p.re = re;
p.nextc(); // load p.ch
return p;
}
-/*
-
-Grammar:
- regexp:
- concatenation { '|' concatenation }
- concatenation:
- { closure }
- closure:
- term [ '*' | '+' | '?' ]
- term:
- '^'
- '$'
- '.'
- character
- '[' [ '^' ] character-ranges ']'
- '(' regexp ')'
-
-*/
-
-func (p *parser) Regexp() (start, end instr)
+func (p *parser) regexp() (start, end instr)
var iNULL instr
return false
}
-func (p *parser) CharClass() instr {
+func (p *parser) charClass() instr {
cc := newCharClass();
- p.re.Add(cc);
+ p.re.add(cc);
if p.c() == '^' {
cc.negate = true;
p.nextc();
switch c := p.c(); c {
case ']', endOfFile:
if left >= 0 {
- p.re.Error(ErrBadRange);
+ p.re.setError(ErrBadRange);
}
return cc;
case '-': // do this before backslash processing
- p.re.Error(ErrBadRange);
+ p.re.setError(ErrBadRange);
case '\\':
c = p.nextc();
switch {
case c == endOfFile:
- p.re.Error(ErrExtraneousBackslash);
+ p.re.setError(ErrExtraneousBackslash);
case c == 'n':
c = '\n';
case specialcclass(c):
// c is as delivered
default:
- p.re.Error(ErrBadBackslash);
+ p.re.setError(ErrBadBackslash);
}
fallthrough;
default:
p.nextc();
left = c;
} else { // single char
- cc.AddRange(c, c);
+ cc.addRange(c, c);
}
case left <= c: // second of pair
- cc.AddRange(left, c);
+ cc.addRange(left, c);
left = -1;
default:
- p.re.Error(ErrBadRange);
+ p.re.setError(ErrBadRange);
}
}
}
return iNULL
}
-func (p *parser) Term() (start, end instr) {
+func (p *parser) term() (start, end instr) {
switch c := p.c(); c {
case '|', endOfFile:
return iNULL, iNULL;
case '*', '+':
- p.re.Error(ErrBareClosure);
+ p.re.setError(ErrBareClosure);
case ')':
if p.nlpar == 0 {
- p.re.Error(ErrUnmatchedRpar);
+ p.re.setError(ErrUnmatchedRpar);
}
return iNULL, iNULL;
case ']':
- p.re.Error(ErrUnmatchedRbkt);
+ p.re.setError(ErrUnmatchedRbkt);
case '^':
p.nextc();
- start = p.re.Add(new(_Bot));
+ start = p.re.add(new(_Bot));
return start, start;
case '$':
p.nextc();
- start = p.re.Add(new(_Eot));
+ start = p.re.add(new(_Eot));
return start, start;
case '.':
p.nextc();
- start = p.re.Add(new(_Any));
+ start = p.re.add(new(_Any));
return start, start;
case '[':
p.nextc();
- start = p.CharClass();
+ start = p.charClass();
if p.c() != ']' {
- p.re.Error(ErrUnmatchedLbkt);
+ p.re.setError(ErrUnmatchedLbkt);
}
p.nextc();
return start, start;
p.nlpar++;
p.re.nbra++; // increment first so first subexpr is \1
nbra := p.re.nbra;
- start, end = p.Regexp();
+ start, end = p.regexp();
if p.c() != ')' {
- p.re.Error(ErrUnmatchedLpar);
+ p.re.setError(ErrUnmatchedLpar);
}
p.nlpar--;
p.nextc();
bra := new(_Bra);
- p.re.Add(bra);
+ p.re.add(bra);
ebra := new(_Ebra);
- p.re.Add(ebra);
+ p.re.add(ebra);
bra.n = nbra;
ebra.n = nbra;
if start == iNULL {
- if end == iNULL { p.re.Error(ErrInternal) }
+ if end == iNULL {
+ p.re.setError(ErrInternal)
+ }
start = ebra
} else {
- end.SetNext(ebra);
+ end.setNext(ebra);
}
- bra.SetNext(start);
+ bra.setNext(start);
return bra, ebra;
case '\\':
c = p.nextc();
switch {
case c == endOfFile:
- p.re.Error(ErrExtraneousBackslash);
+ p.re.setError(ErrExtraneousBackslash);
case c == 'n':
c = '\n';
case special(c):
// c is as delivered
default:
- p.re.Error(ErrBadBackslash);
+ p.re.setError(ErrBadBackslash);
}
fallthrough;
default:
p.nextc();
start = newChar(c);
- p.re.Add(start);
+ p.re.add(start);
return start, start
}
panic("unreachable");
}
-func (p *parser) Closure() (start, end instr) {
- start, end = p.Term();
+func (p *parser) closure() (start, end instr) {
+ start, end = p.term();
if start == iNULL {
return
}
case '*':
// (start,end)*:
alt := new(_Alt);
- p.re.Add(alt);
- end.SetNext(alt); // after end, do 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;
case '+':
// (start,end)+:
alt := new(_Alt);
- p.re.Add(alt);
- end.SetNext(alt); // after end, do 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
case '?':
// (start,end)?:
alt := new(_Alt);
- p.re.Add(alt);
+ p.re.add(alt);
nop := new(_Nop);
- p.re.Add(nop);
+ p.re.add(nop);
alt.left = start; // alternate branch is start
- alt.next = nop; // follow on to nop
- end.SetNext(nop); // after end, go to nop
+ 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
default:
}
switch p.nextc() {
case '*', '+', '?':
- p.re.Error(ErrBadClosure);
+ p.re.setError(ErrBadClosure);
}
return
}
-func (p *parser) Concatenation() (start, end instr) {
+func (p *parser) concatenation() (start, end instr) {
start, end = iNULL, iNULL;
for {
- nstart, nend := p.Closure();
+ nstart, nend := p.closure();
switch {
case nstart == iNULL: // end of this concatenation
if start == iNULL { // this is the empty string
- nop := p.re.Add(new(_Nop));
+ nop := p.re.add(new(_Nop));
return nop, nop;
}
return;
case start == iNULL: // this is first element of concatenation
start, end = nstart, nend;
default:
- end.SetNext(nstart);
+ end.setNext(nstart);
end = nend;
}
}
panic("unreachable");
}
-func (p *parser) Regexp() (start, end instr) {
- start, end = p.Concatenation();
+func (p *parser) regexp() (start, end instr) {
+ start, end = p.concatenation();
for {
switch p.c() {
default:
return;
case '|':
p.nextc();
- nstart, nend := p.Concatenation();
+ nstart, nend := p.concatenation();
alt := new(_Alt);
- p.re.Add(alt);
+ p.re.add(alt);
alt.left = start;
- alt.next = nstart;
+ alt.setNext(nstart);
nop := new(_Nop);
- p.re.Add(nop);
- end.SetNext(nop);
- nend.SetNext(nop);
+ p.re.add(nop);
+ end.setNext(nop);
+ nend.setNext(nop);
start, end = alt, nop;
}
}
}
func unNop(i instr) instr {
- for i.Type() == _NOP {
- i = i.Next()
+ for i.kind() == _NOP {
+ i = i.next()
}
return i
}
-func (re *_RE) EliminateNops() {
+func (re *Regexp) eliminateNops() {
for i := 0; i < re.inst.Len(); i++ {
inst := re.inst.At(i).(instr);
- if inst.Type() == _END {
+ if inst.kind() == _END {
continue
}
- inst.SetNext(unNop(inst.Next()));
- if inst.Type() == _ALT {
+ inst.setNext(unNop(inst.next()));
+ if inst.kind() == _ALT {
alt := inst.(*_Alt);
alt.left = unNop(alt.left);
}
}
}
-func (re *_RE) Dump() {
+func (re *Regexp) dump() {
for i := 0; i < re.inst.Len(); i++ {
inst := re.inst.At(i).(instr);
- print(inst.Index(), ": ");
- inst.Print();
- if inst.Type() != _END {
- print(" -> ", inst.Next().Index())
+ print(inst.index(), ": ");
+ inst.print();
+ if inst.kind() != _END {
+ print(" -> ", inst.next().index())
}
print("\n");
}
}
-func (re *_RE) DoParse() {
+func (re *Regexp) doParse() {
p := newParser(re);
start := new(_Start);
- re.Add(start);
- s, e := p.Regexp();
- start.next = s;
+ re.add(start);
+ s, e := p.regexp();
+ start.setNext(s);
re.start = start;
- e.SetNext(re.Add(new(_End)));
+ e.setNext(re.add(new(_End)));
if debug {
- re.Dump();
+ re.dump();
println();
}
- re.EliminateNops();
+ re.eliminateNops();
if debug {
- re.Dump();
+ re.dump();
println();
}
}
-func compiler(str string, ch chan *_RE) {
- re := new(_RE);
+func compiler(str string, ch chan *Regexp) {
+ re := new(Regexp);
re.expr = str;
re.inst = array.New(0);
re.ch = ch;
- re.DoParse();
+ re.doParse();
ch <- re;
}
-// Public interface has only execute functionality
-type Regexp interface {
- Execute(s string) []int;
- Match(s string) bool;
- MatchStrings(s string) []string;
-}
-
-// Compile in separate goroutine; wait for result
-func Compile(str string) (regexp Regexp, error *os.Error) {
- ch := make(chan *_RE);
+// Compile parses a regular expression and returns, if successful, a Regexp
+// object that can be used to match against text.
+func Compile(str string) (regexp *Regexp, error *os.Error) {
+ // Compile in a separate goroutine and wait for the result.
+ ch := make(chan *Regexp);
go compiler(str, ch);
re := <-ch;
return re, re.error
// Append new state to to-do list. Leftmost-longest wins so avoid
// adding a state that's already active.
func addState(s []state, inst instr, match []int) []state {
- index := inst.Index();
+ index := inst.index();
l := len(s);
pos := match[0];
// TODO: Once the state is a vector and we can do insert, have inputs always
// go in order correctly and this "earlier" test is never necessary,
for i := 0; i < l; i++ {
- if s[i].inst.Index() == index && // same instruction
+ if s[i].inst.index() == index && // same instruction
s[i].match[0] < pos { // earlier match already going; lefmost wins
return s
}
return s;
}
-func (re *_RE) DoExecute(str string, pos int) []int {
+func (re *Regexp) doExecute(str string, pos int) []int {
var s [2][]state; // TODO: use a vector when state values (not ptrs) can be vector elements
s[0] = make([]state, 10)[0:0];
s[1] = make([]state, 10)[0:0];
match[i] = -1; // no match seen; catches cases like "a(b)?c" on "ac"
}
match[0] = pos;
- s[out] = addState(s[out], re.start.Next(), match);
+ s[out] = addState(s[out], re.start.next(), match);
}
in, out = out, in; // old out state is new in state
s[out] = s[out][0:0]; // clear out state
}
for i := 0; i < len(s[in]); i++ {
st := s[in][i];
- switch s[in][i].inst.Type() {
+ switch s[in][i].inst.kind() {
case _BOT:
if pos == 0 {
- s[in] = addState(s[in], st.inst.Next(), st.match)
+ s[in] = addState(s[in], st.inst.next(), st.match)
}
case _EOT:
if pos == len(str) {
- s[in] = addState(s[in], st.inst.Next(), st.match)
+ s[in] = addState(s[in], st.inst.next(), st.match)
}
case _CHAR:
if c == st.inst.(*_Char).char {
- s[out] = addState(s[out], st.inst.Next(), st.match)
+ s[out] = addState(s[out], st.inst.next(), st.match)
}
case _CHARCLASS:
- if st.inst.(*_CharClass).Matches(c) {
- s[out] = addState(s[out], st.inst.Next(), st.match)
+ if st.inst.(*_CharClass).matches(c) {
+ s[out] = addState(s[out], st.inst.next(), st.match)
}
case _ANY:
if c != endOfFile {
- s[out] = addState(s[out], st.inst.Next(), st.match)
+ s[out] = addState(s[out], st.inst.next(), st.match)
}
case _BRA:
n := st.inst.(*_Bra).n;
st.match[2*n] = pos;
- s[in] = addState(s[in], st.inst.Next(), st.match);
+ s[in] = addState(s[in], st.inst.next(), st.match);
case _EBRA:
n := st.inst.(*_Ebra).n;
st.match[2*n+1] = pos;
- s[in] = addState(s[in], st.inst.Next(), st.match);
+ s[in] = addState(s[in], st.inst.next(), st.match);
case _ALT:
s[in] = addState(s[in], st.inst.(*_Alt).left, st.match);
// give other branch a copy of this match vector
for i := 0; i < len(s1); i++ {
s1[i] = st.match[i]
}
- s[in] = addState(s[in], st.inst.Next(), s1);
+ s[in] = addState(s[in], st.inst.next(), s1);
case _END:
// choose leftmost longest
if !found || // first
}
found = true;
default:
- st.inst.Print();
+ st.inst.print();
panic("unknown instruction in execute");
}
}
}
-func (re *_RE) Execute(s string) []int {
- return re.DoExecute(s, 0)
+// Execute 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 value of -1 means the subexpression did not match any element of the string.
+// An empty array means "no match".
+// (Regexp is an internal type that implements the Regexp interface.)
+func (re *Regexp) Execute(s string) (a []int) {
+ return re.doExecute(s, 0)
}
-func (re *_RE) Match(s string) bool {
- return len(re.DoExecute(s, 0)) > 0
+// Match returns whether the Regexp matches the string s.
+// The return value is a boolean: true for match, false for no match.
+// (Regexp is an internal type that implements the Regexp interface.)
+func (re *Regexp) Match(s string) bool {
+ return len(re.doExecute(s, 0)) > 0
}
-func (re *_RE) MatchStrings(s string) []string {
- r := re.DoExecute(s, 0);
+// 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''.
+// (Regexp is an internal type that implements the Regexp interface.)
+func (re *Regexp) MatchStrings(s string) (a []string) {
+ r := re.doExecute(s, 0);
if r == nil {
return nil
}
- a := make([]string, len(r)/2);
+ a = make([]string, len(r)/2);
for i := 0; i < len(r); i += 2 {
- a[i/2] = s[r[i] : r[i+1]]
+ if r[i] != -1 { // -1 means no match for this subexpression
+ a[i/2] = s[r[i] : r[i+1]]
+ }
}
- return a
+ return
}
-// Exported function for simple boolean check. Anything more fancy
-// needs a call to Compile.
+// Match checks whether a textual regular expression
+// matches a substring. More complicated queries need
+// to use Compile and the full Regexp interface.
func Match(pattern string, s string) (matched bool, error *os.Error) {
re, err := Compile(pattern);
if err != nil {