PATTERNS(2)           Icon Program Library            PATTERNS(2)



NNNNAAAAMMMMEEEE
     patterns - SNOBOL4-style pattern matching

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     These procedures are adapted from TR 80-25 and TR 81-6. They
     provide procedural equivalents for most SNOBOL4 patterns and
     some extensions.

SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
     AAAAnnnncccchhhhoooorrrr(((())))       &&&&AAAANNNNCCCCHHHHOOOORRRR ==== 1111  if MMMMooooddddeeee ::::==== AAAAnnnncccchhhhoooorrrr
     AAAAnnnnyyyy((((ssss))))         AAAANNNNYYYY((((SSSS))))
     AAAAppppppppllllyyyy((((ssss,,,,pppp))))     SSSS ???? PPPP
     AAAArrrrbbbb(((())))          AAAARRRRBBBB
     AAAArrrrbbbbnnnnoooo((((pppp))))       AAAARRRRBBBBNNNNOOOO((((PPPP))))
     AAAArrrrbbbbxxxx((((iiii))))        AAAARRRRBBBB((((IIII))))
     BBBBaaaallll(((())))          BBBBAAAALLLL
     BBBBrrrreeeeaaaakkkk((((ssss))))       BBBBRRRREEEEAAAAKKKK((((SSSS))))
     BBBBrrrreeeeaaaakkkkxxxx((((ssss))))      BBBBRRRREEEEAAAAKKKKXXXX((((SSSS))))
     CCCCaaaatttt((((pppp1111,,,,pppp2222))))     PPPP1111 PPPP2222
     DDDDiiiissssccccaaaarrrrdddd((((pppp))))     ////PPPP
     EEEExxxxoooogggg((((ssss))))        \\\\SSSS
     FFFFiiiinnnndddd((((ssss))))        FFFFIIIINNNNDDDD((((SSSS))))
     FFFFllllooooaaaatttt(((())))        &&&&AAAANNNNCCCCHHHHOOOORRRR ==== 0000  if MMMMooooddddeeee ::::==== FFFFllllooooaaaatttt
     LLLLeeeennnn((((iiii))))         LLLLEEEENNNN((((IIII))))
     LLLLiiiimmmmiiiitttt((((pppp,,,,iiii))))     PPPP \\\\ iiii
     LLLLooooccccaaaatttteeee((((pppp))))      LLLLOOOOCCCCAAAATTTTEEEE((((PPPP))))
     MMMMaaaarrrrbbbb(((())))         longest-first AAAARRRRBBBB
     MMMMooooddddeeee(((())))         Anchored or unanchored matching (see AAAAnnnncccchhhhoooorrrr and FFFFllllooooaaaatttt)
     NNNNoooottttaaaannnnyyyy((((ssss))))      NNNNOOOOTTTTAAAANNNNYYYY((((SSSS))))
     PPPPoooossss((((iiii))))         PPPPOOOOSSSS((((IIII))))
     RRRReeeeppppllllaaaacccceeee((((pppp,,,,ssss))))   PPPP =_=_=_=_ SSSS
     RRRRppppoooossss((((iiii))))        RRRRPPPPOOOOSSSS((((IIII))))
     RRRRttttaaaabbbb((((iiii))))        RRRRTTTTAAAABBBB((((IIII))))
     SSSSppppaaaannnn((((ssss))))        SSSSPPPPAAAANNNN((((SSSS))))
     SSSSttttrrrriiiinnnngggg((((ssss))))      SSSS
     SSSSuuuucccccccceeeeeeeedddd(((())))      SSSSUUUUCCCCCCCCEEEEEEEEDDDD
     TTTTaaaabbbb((((iiii))))         TTTTAAAABBBB((((IIII))))
     XXXXffffoooorrrrmmmm((((ffff,,,,pppp))))     FFFF((((PPPP))))

     In addition to the procedures above, the following expres-
     sions can be used:

     pppp1111(((()))) |||| pppp2222(((())))    PPPP1111 |||| PPPP2222
     vvvv <<<<---- pppp(((())))       PPPP .... VVVV (approximate)
     vvvv ::::==== pppp(((())))       PPPP $$$$ VVVV (approximate)
     ffffaaaaiiiillll           FFFFAAAAIIIILLLL
     ====ssss             SSSS (in place of SSSSttttrrrriiiinnnngggg((((ssss)))))
     pppp1111(((()))) |||||||| pppp2222(((())))   PPPP1111 PPPP2222 (in place of CCCCaaaatttt((((pppp1111,,,,pppp2222)))))


     Using this system, most SNOBOL4 patterns can be satisfac-
     torily transliterated into Icon procedures and expressions.



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PATTERNS(2)           Icon Program Library            PATTERNS(2)



     For example, the pattern

          SPAN("0123456789") $ N "H" LEN(*N) $ LITERAL

     can be transliterated into

          (n <- Span('0123456789')) || ="H" || (literal <- Len(n))

     Concatenation of components is necessary to preserve the
     pattern-matching properties of SNOBOL4.  See the documents
     listed below for details and limitations.

CCCCAAAAVVVVEEEEAAAATTTTSSSS
     Simulating SNOBOL4 pattern matching using the procedures
     above is inefficient.

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     Ralph E. Griswold. _P_a_t_t_e_r_n _M_a_t_c_h_i_n_g _i_n _I_c_o_n, TR 80-25, The
     University of Arizona, 1980.

     Ralph E. Griswold. _M_o_d_e_l_s _o_f _S_t_r_i_n_g _P_a_t_t_e_r_n _M_a_t_c_h_i_n_g, TR
     81-6, Department of Computer Science, The University of
     Arizona, 1981.

     Ralph E. Griswold. ``Implementing SNOBOL4 Pattern Matching
     in Icon'', _C_o_m_p_u_t_e_r _L_a_n_g_u_a_g_e_s, Vol. 8, No. 8 (1983), pp.
     77-92.

AAAAUUUUTTTTHHHHOOOORRRR
     Ralph E. Griswold

























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