#

## Issue RANGE-OF-START-AND-END-PARAMETERS Writeup

    Issue:        RANGE-OF-START-AND-END-PARAMETERS
    References:   COUNT (p257), COUNT-IF (p257), COUNT-IF-NOT (p257),
    	      DELETE (p257), DELETE-DUPLICATES (p254), DELETE-IF (p254),
    	      DELETE-IF-NOT (p254), FILL (p252), FIND (p257), FIND-IF (p257),
    	      FIND-IF-NOT (p257), MAKE-STRING-INPUT-STREAM (p330),
    	      MISMATCH (p257), NSTRING-CAPITALIZE (p304),
    	      NSTRING-DOWNCASE (p304), NSTRING-UPCASE (p304), SUBSTITUTE (p255),
    	      NSUBSTITUTE-IF (p256), NSUBSTITUTE-IF-NOT (p256),
    	      PARSE-INTEGER (p381), PARSE-NAMESTRING (p414), POSITION (p257),
    	      POSITION-IF (p257), POSITION-IF-NOT (p257),
    	      READ-FROM-STRING (p381), REDUCE (p251), REMOVE (p253),
    	      REMOVE-DUPLICATES (p254), REMOVE-IF (p253), REMOVE-IF-NOT (p253),
    	      REPLACE (p252), SEARCH (p258), STRING-CAPITALIZE (p303),
    	      STRING-EQUAL (p301), STRING-DOWNCASE (p303), STRING-GREATERP (p302),
    	      STRING-LESSP (p302), STRING-NOT-EQUAL (p302),
    	      STRING-NOT-GREATERP (p302), STRING-NOT-LESSP (p302),
    	      STRING-UPCASE (p303), STRING/= (p301), STRING< (p301),
    	      STRING<= (p301), STRING= (p300), STRING> (p301), STRING>= (p301),
    	      SUBSEQ (p248), SUBSTITUTE (p255), SUBSTITUTE-IF (p255),
    	      SUBSTITUTE-IF-NOT (p255), WRITE-LINE (p384), WRITE-STRING (p384)
    Category:     CLARIFICATION
    Edit history: 14-Sep-88, Version 1 by Pitman

    Problem Description:

      CLtL is not always clear about the possible values which the START and END
      parameters of built-in Common Lisp can take.

    Proposal (RANGE-OF-START-AND-END-PARAMETERS:INTEGER-AND-INTEGER-NIL):

      Clarify that for functions permitting a parameter named START, START1,
      or START2 which delimits the beginning point in a sequence to be
      considered for some operation, that paremeter must be a non-negative
      integer. If the argument is optional or key (as is the case for all
      functions referenced above except SUBSEQ), the value will default to
      0 if not supplied. It is not permissible to pass NIL as this argument.

      Clarify that for functions permitting a parameter named END, END1,
      or END2 which delimits the end point in a sequence to be considered
      for some operation, that paremeter must be a non-negative integer
      indicating a termination point or NIL indicating the last element
      in the sequence. If the argument is optional or key (as is the case
      for all functions referenced above), the value will default to NIL
      if not supplied. Supplying NIL is, therefore, equivalent to not
      supplying this argument.

    Test Case:

      (SEARCH "F" "FOO" :START1 NIL) is an error.

      (SEARCH "F" "FOO" :START2 0) is permissible and is equivalent to
      (SEARCH "F" "FOO")

      (SEARCH "F" "FOO" :END2 NIL) is permissible and is equivalent to
      (SEARCH "F" "FOO")

    Rationale:

      To keep data flow between programs from becoming excessively complicated,
      it's a good idea to specify what the default values are so that they can
      be passed explicitly rather than requiring an alternate calling sequence
      for all possible cases where the value might need to default.

    Current Practice:

      Symbolics Genera implements the proposed behavior.

    Cost to Implementors:

      Hopefully most implementations already do this. Those that do not will
      probably have to make quite a number of small changes to both the code
      for these functions and to any associated compiler optimizers.

    Cost to Users:

      This change is upward compatible with existing user code. Any program
      which did not conform to this proposal was already not portable.

    Cost of Non-Adoption:

      Subtle gratuitous differences in the handling of these arguments would
      continue to be a possibility and a barrier to portability.

    Benefits:

      The language would be more regular and well-defined.

    Aesthetics:

      If it makes things clearer, it's an improvement.

    Discussion:

      Pitman supports RANGE-OF-START-AND-END-PARAMETERS:INTEGER-AND-INTEGER-NIL.

Copyright 1996-2001, Xanalys Inc. All rights reserved.