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Annotation of researchv10dc/cmd/icon/ipl/source/lmap.icn, revision 1.1

1.1     ! root        1: #      LMAP
        !             2: #
        !             3: #      Map list
        !             4: #
        !             5: #      Ralph E. Griswold
        !             6: #
        !             7: #      Last modified 12/15/85
        !             8: #
        !             9: 
        !            10: # This procedure is modeled after the built-in string mapping function.
        !            11: # The main difference is that the first argument is modified, rather
        !            12: # than constructing a new list. This is in the interests of efficiency
        !            13: # and likely uses, but is easily changed.
        !            14: #
        !            15: # Warning:  a2 and a3 are cached so that the table of correspondences
        !            16: # is not rebuilt if lmap is called successively with the same mapping
        !            17: # lists. Just because a2 and a3 are the same does not mean that they
        !            18: # have the same values on successive calls of lmap. Thus, the
        !            19: # equivalence of maps is taken from the value of a2 and a3, not their
        !            20: # respective elements. This is deliberate, but could result in
        !            21: # unexpected results.
        !            22: 
        !            23: procedure lmap(a1,a2,a3)
        !            24:    static lmem2, lmem3, lmaptbl, tdefault
        !            25:    local i
        !            26:    initial tdefault := []
        !            27:    if not(type(a1) == type(a2) == type(a3) == "list")
        !            28:       then stop("illegal type in lmap")
        !            29:    if not(*a2 = *a3)
        !            30:       then stop("Run-time error:\nSecond and third arguments of lmap differ in length")
        !            31:    if not(lmem2 === a2 & lmem3 === a3) then {  # if an argument is new, rebuild
        !            32:       lmem2 := a2                              # save for future reference
        !            33:       lmem3 := a3
        !            34:       lmaptbl := table(tdefault)               # new mapping table
        !            35:       every i := 1 to *a2 do                   # build the map
        !            36:          lmaptbl[a2[i]] := a3[i]
        !            37:       }
        !            38:    every i := 1 to *a1 do                      # map the values
        !            39:       a1[i] := (tdefault ~=== lmaptbl[a1[i]])
        !            40:    return a1
        !            41: end

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