patterns.icn

File patterns.icn

Summary

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	File:     patterns.icn

	Subject:  Procedures for SNOBOL4-style pattern matching

	Author:   Ralph E. Griswold

	Date:     June 10, 1988

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   This file is in the public domain.

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  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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Procedures: