ref: da7d6df6faf18e289fe0f3f61524dcc7fddeef18
dir: /appl/lib/regex.b/
implement Regex;
include "regex.m";
# syntax
# RE ALT regular expression
# NUL
# ALT CAT alternation
# CAT | ALT
#
# CAT DUP catenation
# DUP CAT
#
# DUP PRIM possibly duplicated primary
# PCLO
# CLO
# OPT
#
# PCLO PRIM + 1 or more
# CLO PRIM * 0 or more
# OPT PRIM ? 0 or 1
#
# PRIM ( RE )
# ()
# DOT any character
# CHAR a single character
# ESC escape sequence
# [ SET ] character set
# NUL null string
# HAT beginning of string
# DOL end of string
#
NIL : con -1; # a refRex constant
NONE: con -2; # ditto, for an un-set value
BAD: con 1<<16; # a non-character
HUGE: con (1<<31) - 1;
# the data structures of re.m would like to be ref-linked, but are
# circular (see fn walk), thus instead of pointers we use indexes
# into an array (arena) of nodes of the syntax tree of a regular expression.
# from a storage-allocation standpoint, this replaces many small
# allocations of one size with one big one of variable size.
ReStr: adt {
s : string;
i : int; # cursor postion
n : int; # number of chars left; -1 on error
peek : fn(s: self ref ReStr): int;
next : fn(s: self ref ReStr): int;
};
ReStr.peek(s: self ref ReStr): int
{
if(s.n <= 0)
return BAD;
return s.s[s.i];
}
ReStr.next(s: self ref ReStr): int
{
if(s.n <= 0)
return BAD;
s.n--;
return s.s[s.i++];
}
newRe(kind: int, left, right: refRex, set: ref Set, ar: ref Arena, pno: int): refRex
{
ar.rex[ar.ptr] = Rex(kind, left, right, set, pno);
return ar.ptr++;
}
# parse a regex by recursive descent to get a syntax tree
re(s: ref ReStr, ar: ref Arena): refRex
{
left := cat(s, ar);
if(left==NIL || s.peek()!='|')
return left;
s.next();
right := re(s, ar);
if(right == NIL)
return NIL;
return newRe(ALT, left, right, nil, ar, 0);
}
cat(s: ref ReStr, ar: ref Arena): refRex
{
left := dup(s, ar);
if(left == NIL)
return left;
right := cat(s, ar);
if(right == NIL)
return left;
return newRe(CAT, left, right, nil, ar, 0);
}
dup(s: ref ReStr, ar: ref Arena): refRex
{
case s.peek() {
BAD or ')' or ']' or '|' or '?' or '*' or '+' =>
return NIL;
}
prim: refRex;
case kind:=s.next() {
'(' => if(ar.pno < 0) {
if(s.peek() == ')') {
s.next();
prim = newRe(NUL, NONE, NONE, nil, ar, 0);
} else {
prim = re(s, ar);
if(prim==NIL || s.next()!=')')
s.n = -1;
}
} else {
pno := ++ar.pno;
lp := newRe(LPN, NONE, NONE, nil, ar, pno);
rp := newRe(RPN, NONE, NONE, nil, ar, pno);
if(s.peek() == ')') {
s.next();
prim = newRe(CAT, lp, rp, nil, ar, 0);
} else {
prim = re(s, ar);
if(prim==NIL || s.next()!=')')
s.n = -1;
else {
prim = newRe(CAT, prim, rp, nil, ar, 0);
prim = newRe(CAT, lp, prim, nil, ar, 0);
}
}
}
'[' => prim = newRe(SET, NONE, NONE, newSet(s), ar, 0);
* => case kind {
'.' => kind = DOT;
'^' => kind = HAT;
'$' => kind = DOL;
}
prim = newRe(esc(s, kind), NONE, NONE, nil, ar, 0);
}
case s.peek() {
'*' => kind = CLO;
'+' => kind = PCLO;
'?' => kind = OPT;
* => return prim;
}
s.next();
return newRe(kind, prim, NONE, nil, ar, 0);
}
esc(s: ref ReStr, char: int): int
{
if(char == '\\') {
char = s.next();
case char {
BAD => s.n = -1;
'n' => char = '\n';
}
}
return char;
}
# walk the tree adjusting pointers to refer to
# next state of the finite state machine
walk(r: refRex, succ: refRex, ar: ref Arena)
{
if(r==NONE)
return;
rex := ar.rex[r];
case rex.kind {
ALT => walk(rex.left, succ, ar);
walk(rex.right, succ, ar);
return;
CAT => walk(rex.left, rex.right, ar);
walk(rex.right, succ, ar);
ar.rex[r] = ar.rex[rex.left]; # optimization
return;
CLO or PCLO =>
end := newRe(OPT, r, succ, nil, ar, 0); # here's the circularity
walk(rex.left, end, ar);
OPT => walk(rex.left, succ, ar);
}
ar.rex[r].right = succ;
}
compile(e: string, flag: int): (Re, string)
{
if(e == nil)
return (nil, "missing expression");
s := ref ReStr(e, 0, len e);
ar := ref Arena(array[2*s.n] of Rex, 0, 0, (flag&1)-1);
start := ar.start = re(s, ar);
if(start==NIL || s.n!=0)
return (nil, "invalid regular expression");
walk(start, NIL, ar);
if(ar.pno < 0)
ar.pno = 0;
return (ar, nil);
}
# todo1, todo2: queues for epsilon and advancing transitions
Gaz: adt {
pno: int;
beg: int;
end: int;
};
Trace: adt {
cre: refRex; # cursor in Re
beg: int; # where this trace began;
gaz: list of Gaz;
};
Queue: adt {
ptr: int;
q: array of Trace;
};
execute(re: Re, s: string): array of (int, int)
{
return executese(re, s, (-1,-1), 1, 1);
}
executese(re: Re, s: string, range: (int, int), bol: int, eol: int): array of (int,int)
{
if(re==nil)
return nil;
(s0, s1) := range;
if(s0 < 0)
s0 = 0;
if(s1 < 0)
s1 = len s;
gaz : list of Gaz;
(beg, end) := (-1, -1);
todo1 := ref Queue(0, array[re.ptr] of Trace);
todo2 := ref Queue(0, array[re.ptr] of Trace);
for(i:=s0; i<=s1; i++) {
small2 := HUGE; # earliest possible match if advance
if(beg == -1) # no leftmost match yet
todo1.q[todo1.ptr++] = Trace(re.start, i, nil);
for(k:=0; k<todo1.ptr; k++) {
q := todo1.q[k];
rex := re.rex[q.cre];
next1 := next2 := NONE;
case rex.kind {
NUL =>
next1 = rex.right;
DOT =>
if(i<len s && s[i]!='\n')
next2 = rex.right;
HAT =>
if(i == s0 && bol)
next1 = rex.right;
DOL =>
if(i == s1 && eol)
next1 = rex.right;
SET =>
if(i<len s && member(s[i], rex.set))
next2 = rex.right;
CAT or
PCLO =>
next1 = rex.left;
ALT or
CLO or
OPT =>
next1 = rex.right;
k = insert(rex.left, q.beg, q.gaz, todo1, k);
LPN =>
next1 = rex.right;
q.gaz = Gaz(rex.pno,i,-1)::q.gaz;
RPN =>
next1 = rex.right;
for(r:=q.gaz; ; r=tl r) {
(pno,beg1,end1) := hd r;
if(rex.pno==pno && end1==-1) {
q.gaz = Gaz(pno,beg1,i)::q.gaz;
break;
}
}
* =>
if(i<len s && rex.kind==s[i])
next2 = rex.right;
}
if(next1 != NONE) {
if(next1 != NIL)
k =insert(next1, q.beg, q.gaz, todo1, k);
else if(better(q.beg, i, beg, end))
(gaz, beg, end) = (q.gaz, q.beg, i);
}
if(next2 != NONE) {
if(next2 != NIL) {
if(q.beg < small2)
small2 = q.beg;
insert(next2, q.beg, q.gaz, todo2, 0);
} else if(better(q.beg, i+1, beg, end))
(gaz, beg, end) = (q.gaz, q.beg, i+1);
}
}
if(beg!=-1 && beg<small2) # nothing better possible
break;
(todo1,todo2) = (todo2, todo1);
todo2.ptr = 0;
}
if(beg == -1)
return nil;
result := array[re.pno+1] of { 0 => (beg,end), * => (-1,-1) };
for( ; gaz!=nil; gaz=tl gaz) {
(pno, beg1, end1) := hd gaz;
(rbeg, nil) := result[pno];
if(rbeg==-1 && (beg1|end1)!=-1)
result[pno] = (beg1,end1);
}
return result;
}
better(newbeg, newend, oldbeg, oldend: int): int
{
return oldbeg==-1 || newbeg<oldbeg ||
newbeg==oldbeg && newend>oldend;
}
insert(next: refRex, tbeg: int, tgaz: list of Gaz, todo: ref Queue, k: int): int
{
for(j:=0; j<todo.ptr; j++)
if(todo.q[j].cre == next)
if(todo.q[j].beg <= tbeg)
return k;
else
break;
if(j < k)
k--;
if(j < todo.ptr)
todo.ptr--;
for( ; j<todo.ptr; j++)
todo.q[j] = todo.q[j+1];
todo.q[todo.ptr++] = Trace(next, tbeg, tgaz);
return k;
}
ASCII : con 128;
WORD : con 32;
member(char: int, set: ref Set): int
{
if(char < 128)
return ((set.ascii[char/WORD]>>char%WORD)&1)^set.neg;
for(l:=set.unicode; l!=nil; l=tl l) {
(beg, end) := hd l;
if(char>=beg && char<=end)
return !set.neg;
}
return set.neg;
}
newSet(s: ref ReStr): ref Set
{
set := ref Set(0, array[ASCII/WORD] of {* => 0}, nil);
if(s.peek() == '^') {
set.neg = 1;
s.next();
}
while(s.n > 0) {
char1 := s.next();
if(char1 == ']')
return set;
char1 = esc(s, char1);
char2 := char1;
if(s.peek() == '-') {
s.next();
char2 = s.next();
if(char2 == ']')
break;
char2 = esc(s, char2);
if(char2 < char1)
break;
}
for( ; char1<=char2; char1++)
if(char1 < ASCII)
set.ascii[char1/WORD] |= 1<<char1%WORD;
else {
set.unicode = (char1,char2)::set.unicode;
break;
}
}
s.n = -1;
return nil;
}