TIP #429: A 'STRING' SUBCOMMAND FOR CONCATENATION 
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 Version:      $Revision: 1.6 $
 Author:       Andreas Leitgeb <avl_at_logic.at>
               Alexandre Ferrieux <alexandre.ferrieux_at_gmail.com>
 State:        Final
 Type:         Project
 Tcl-Version:  8.6.2
 Vote:         Done
 Created:      Sunday, 27 July 2014
 URL:          https://tip.tcl-lang.org429.html
 Post-History: 

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 ABSTRACT 
==========

 This TIP describes a new (sub)command *string cat* to concatenate an 
 arbitrary number of strings. 

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

 Tcl has string concatenation built-in. But that is lacking in two 
 specific cases: 

     * one cannot directly concat a braced string with anything else 

     * scriptlets such as used for *lmap* are expected to contain 
       commands, the last one of which returns a value. To have the 
       scriptlet return a concatenated string or even just a single 
       string literal, one currently needs to misuse some corner-case of 
       a non-trivial command, like *return -level 0 $x$y* or *string map 
       {} "$x$y"* just to have the scriptlet produce the string as its 
       result. 

 PROPOSAL 
==========

 I propose a new subcommand *string cat*, that will take an arbitrary 
 number of arguments (i.e., 0 or more), and concatenate them into a 
 single string that becomes the result of the command. 

 It would be equivalent to creating a *list* of the separate arguments 
 and use *join* on that list with an empty string as second argument. 

 Compiling that new command to bytecode should be trivial, as 
 concatenation of strings is already compileable. The added value would 
 be allowing braced string literals to be involved, and promoting the 
 resulting stack-item to the result of the command/scriptlet. (This 
 simple compileability is also meant to be a main advantage over *join 
 [list ...] ""*, where the contents of the intermediate list are either 
 a single word or many words, or *lindex [list ...] 0* where the 
 contents of the intermediate list are a single word.) 

 The following equality will hold for any arbitrary contents of the 
 variables *a* and *b*: 

    string equals $a$b [string cat $a $b]

 REJECTED ALTERNATIVES 
=======================

 Lars has mailed on tclcore that TclX has a command *cconcat* that does 
 essentially what my proposed *string cat* is supposed to do (not sure 
 though whether that is compiled). This proposal sticks to the *cat* 
 subcommand, as that is generally the preferred way over new toplevel 
 commands. 

 Also, *string concat* is added to this section, for it is a bit longer 
 than *string cat*, and (as Lars put it) *string cat* is less likely to 
 be misinterpreted as "concat, just moved into the string ensemble." 

 REFERENCE IMPLEMENTATION 
==========================

 Available as branch tip-429 on core.tcl.tk. 

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

 This document has been placed in the public domain. 

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