TIP:		273
Title:		Add Tcl_Expr... Support to Tcl_Get... Functions
Version:	$Revision: 1.5 $
Author:		Carsten Gosvig <tcl@javalite.com>
State:		Rejected
Type:		Project
Vote:		Done
Created:	30-Aug-2006
Post-History:	
Tcl-Version:	8.5
Obsoletes:	176

~Abstract

This TIP proposes adding '''Tcl_Expr'''... calls to '''Tcl_Get'''... functions,
supporting direct use of expressions for arguments to commands that is defined
as int, long, wide-int, double or boolean.

~Rationale

Many of Tcl's commands takes an int, long, wide-int, double or boolean as an
argument. For list and string commands even in the format of '''end-'''''N''.
However, this is limited to a direct string conversion of the argument to one
of the mentioned types, so for even simple expression the '''expr''' command
has to be called explicitly, which is quite cumbersome as can be seen in the
following examples:

|set x [lsearch $list $elem]
|set new [lrange $list [expr $x-1] [expr $x+1]]
|
|set x [string first $string "foo"]
|set new [string range $string $x [expr [$x+5]]
|
|set x [lsearch $list $elem]
|set hex [format "%X" [expr {$x & 0xFF}]]
|
|set file [open $name]
|set buf [read $file [expr {$len * 2 - 10}]]
|
|incr var [expr $step*5+1]
|after [expr $sec*1000]

~Specification

By adding a call to a '''Tcl_Expr'''... function at the point where the
current conversion fails in the '''Tcl_Get'''... functions (at the label named
''bad'' in the current implementation) we will add support for using
expressions directly as arguments without needing to go through the '''expr'''
command:

|set x [lsearch $list $elem]
|set new [lrange $list $x-1 $x+1]
|
|set x [string first $string "foo"]
|set new [string range $string $x $x+5]
|
|set x [lsearch $list $elem]
|set hex [format "%X" {$x & 0xFF}]
|
|set file [open $name]
|set buf [read $file {$len * 2 - 10}]
|
|incr var $step*5+1
|after $sec*1000

This TIP does not propose any alterations to any function or procedure
signatures.

~~Implementation Notes

The '''Tcl_Get'''<''Type''> functions needs to be updated with a call to the
'''Tcl_Expr'''<''Type''> functions, and the
'''Tcl_Get'''<''Type''>'''FromObj''' functions need to be updated with a call
to the '''Tcl_Expr'''<''Type''>'''Obj''' functions.

~~Compatibility

There should be no compability issues, as this TIP only adds functionality to
a current error situation.

This proposal renders [176] obsolete, as that describes a solution that is
effectively a subset of this TIP.

~Copyright

This document has been placed in the public domain.