**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.

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