TIP #292: Allow Unquoted Strings in Expressions
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TIP:	292
Title:	Allow Unquoted Strings in Expressions
Version:	$Revision: 1.3 $
Authors:	Brian Griffin <bgriffin@model.com>
State:	Draft
Type:	Project
Tcl-Version:	8.7
Vote:	Pending
Created:	Wed Nov 01 00:00:00 UTC 2006
Keywords:	Tcl, expr
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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