Issue IN-SYNTAX Writeup

Status: Passed, Mar 89 X3J13

Issue: IN-SYNTAX

Edit History: 21-Oct-88, Version 1 by Pitman

		Version 2, KMP 3/30/89

		Version 3,  9-Apr-89, Masinter

			(Include discussion from Version 1)


Problem Description:


  There is no way to bind read syntax within a file.


  As a result, applications which require extended syntax of some sort

  tend to globally modify the lisp readtable at compile and load time,

  sometimes interfering with other modules and/or user interaction.


  Conscientious developers often avoid the creation of any stylized

  syntax because of its likely effect on parts of the environment which

  don't really belong to the application developer. This need for

  paranoia is probably contrived and the result of what amounts to

  an oversight in the design of Common Lisp.



Proposal (IN-SYNTAX:MINIMAL):


    Define that COMPILE-FILE and LOAD bind *READTABLE* to its current value.


Rationale:


   This allows portable programs to do


     (IN-PACKAGE "FOO")

     (EVAL-WHEN (EVAL LOAD COMPILE)

       (SETQ *READTABLE* FOO:MY-READTABLE))


   at the top of a file without globally side-effecting the

   environment.


   Currently, there is no portable way to change the syntax only for

   the duration of a file, which in turn makes customized syntax

   difficult to use safely.


   Programs that want to side effect the environment can instead

   continue to modify *READTABLE*.


    This is enough of a foothold to implement a more elaborate facility

    for using readtables in a localized way.



Current Practice:


   mixed


Cost to Implementors:


  Very small.


Cost to Users:


small


Cost of Non-Adoption:


  Readtables would continue to be hard to use in a clean way.


Benefits:


  If people could use readtables safely, we might see more interesting

  experimentation with read syntax.


Aesthetics:


  A slight improvement to aesthetics by controlling what was formerly

  an unbounded side-effect (modification to the global readtable).