link patterns
June 10, 1988; Ralph E. Griswold
This file is in the public domain.
These procedures provide procedural equivalents for most SNOBOL4
patterns and some extensions.
Procedures and their pattern equivalents are:
Any(s) ANY(S)
Arb() ARB
Arbno(p) ARBNO(P)
Arbx(i) ARB(I)
Bal() BAL
Break(s) BREAK(S)
Breakx(s) BREAKX(S)
Cat(p1,p2) P1 P2
Discard(p) /P
Exog(s) \S
Find(s) FIND(S)
Len(i) LEN(I)
Limit(p,i) P \ i
Locate(p) LOCATE(P)
Marb() longest-first ARB
Notany(s) NOTANY(S)
Pos(i) POS(I)
Replace(p,s) P = S
Rpos(i) RPOS(I)
Rtab(i) RTAB(I)
Span(s) SPAN(S)
String(s) S
Succeed() SUCCEED
Tab(i) TAB(I)
Xform(f,p) F(P)
The following procedures relate to the application and control
of pattern matching:
Apply(s,p) S ? P
Mode() anchored or unanchored matching (see Anchor
and Float)
Anchor() &ANCHOR = 1 if Mode := Anchor
Float() &ANCHOR = 0 if Mode := Float
In addition to the procedures above, the following expressions
can be used:
p1() | p2() P1 | P2
v <- p() P . V (approximate)
v := p() P $ V (approximate)
fail FAIL
=s S (in place of String(s))
p1() || p2() P1 P2 (in place of Cat(p1,p2))
Using this system, most SNOBOL4 patterns can be satisfactorily
transliterated into Icon procedures and expressions. For example,
the pattern
SPAN("0123456789") $ N "H" LEN(*N) $ LIT
can be transliterated into
(n <- Span('0123456789')) || ="H" ||
(lit <- Len(n))
Concatenation of components is necessary to preserve the
pattern-matching properties of SNOBOL4.
Caveats: Simulating SNOBOL4 pattern matching using the procedures
above is inefficient.