[TCLCORE] TIP #292: Allow Unquoted Strings in Expressions

[Brian G. <bgr...@mo...>]

 TIP #292: ALLOW UNQUOTED STRINGS IN EXPRESSIONS 
=================================================
 Version:      $Revision: 1.1 $
 Author:       Brian Griffin <bgriffin_at_model.com>
 State:        Draft
 Type:         Project
 Tcl-Version:  8.5
 Vote:         Pending
 Created:      Wednesday, 01 November 2006
 URL:          http://purl.org/tcl/tip/292.html
 WebEdit:      http://purl.org/tcl/tip/edit/292
 Post-History: 

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 ABSTRACT 
==========

 This TIP proposes allowing unquoted words to be recognized as strings 
 in expressions (*expr*, *if*, *while*). 

 RATIONALE 
===========

 Currently the following fails with a syntax error: 

       set foo bar
       expr {$foo eq bar}

 This seems antithetical to the EIAS Tao of Tcl. The *set* command does 
 not require the quotes, so why should *expr*, especially since the 
 operands of the *eq* and *ne* operators are treated as strings. It also 
 seems reasonable for the *==* and *!=* operators to reject unquoted 
 strings as not a valid operand. This provides some enforcement for 
 numerical vs. string comparison by forcing the use of quotes to convert 
 the numeric *==* to a string equality test. 

 The rationale for making such a change is it will make complex code a 
 bit easier to read. For example, I can: 

           set var ENUM_VALUE_ONE
   
           switch $var {
                   ENUM_VALUE_ZERO { ... }
                   ENUM_VALUE_ONE  { ... }
                   default { ... }
           }
   
           if {[lsearch $supplied_values ENUM_VALUE_ONE] >= 0} { ... }
   
           if {[string equals $var ENUM_VALUE_ONE]} { ... }

 but I must: 

           if {$var eq "ENUM_VALUE_ONE"} { ... }

 which could lead someone reading the code to incorrectly conclude that 
 ENUM_VALUE_ONE is not the same thing as "ENUM_VALUE_ONE" or miss the 
 fact that they are the same, especially when using a syntax 
 highlighting editor. 

 PROPOSED CHANGE 
=================

 Change the expression parser to accept unquoted words that are not 
 function names as strings. Modify /EqualityExpr/ to reject unqoted 
 strings for "*==*", but allow them for "*eq*". 

 DRAFT IMPLEMENTATION 
======================

 None, at the moment. 

 COPYRIGHT 
===========

 This document has been placed in the public domain. 

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