# TIP 347: Align 'string is ...' to Type-Conversion Functions in 'expr'
	Author:         Jos Decoster <jos.decoster@gmail.com>
	State:          Withdrawn
	Type:           Project
	Vote:           Pending
	Created:        09-Feb-2009
	Post-History:   
	Discussions-To: news:comp.lang.tcl
	Keywords:       Tcl
	Tcl-Version:    8.7
	Obsoleted-By:	395
-----

# Abstract

The **string** command supports tests for a number of Tcl's basic types, for
example, integers, doubles, and booleans. 
The **tcl::mathfunc** mathematical functions provides sevaral functions to
limit the number of bits used in integer numbers. 
This TIP proposes to align both groups of functions for **int**, **long**,
**wide** and **entier**.

# Rationale

The **string** command includes tests for the common Tcl types: **string is
boolean**, **string is double** and **string is integer**. Some of the
integer ranges used in Tcl internals are missing from the list, making it
difficult for an input validation procedure to determine whether, in fact, a
string contains a valid integer number to be used for that specific Tcl
command. 

Ranges already present are:

 * **integer**

 * **wideinteger**

Missing ranges are:

 * **long**

 * **entier**

The **::tcl::mathfunc** mathematical functions provides sevaral functions to
limit the number of bits used in integer numbers. Some of the integer ranges
used in Tcl internals are missing from the list, and other check an unexpected
range. 

Functions already present are:

 * **wide**

 * **entier**

Functions already present but with unexpected behavior are:

 * **int** actually does a **long** conversion

Missing functions are:

 * **long**

Providing a **string is** function for every integer range used in Tcl
internals will make it possible to check every argument in input validation
procedures before calling a Tcl command. Providing **::tcl::mathfunc** for
every integer range used in Tcl internals will make it possible to create values
in a valid range before calling a Tcl command.

Having the same integer range names in the **string is** functions and in the
**::tcl::mathfunc** when they act on the same integer ranges would make the
commands easier to recognise.

# Specification

This document proposes:

 * augmenting the **string is** command with a **string is long** that
functions the same as **string is integer** in every respect except for the
fact that it accepts any string containing a substring that is valid as a long
integer \(that is, acceptable to _Tcl\_GetLongFromObj_\) possibly surrounded by
whitespace.

 * augmenting the **string is** command with a **string is entier** that
functions the same as **string is integer** in every respect except for the
fact that it accepts any string containing a substring that is valid as a bignum
integer \(that is, acceptable to _Tcl\_GetBignumFromObj_\) possibly surrounded by
whitespace.

 * modifying the **::tcl::mathfunc::int** to convert to an integer \(that is,
acceptable to _Tcl\_GetIntFromObj_\).

 * adding the **::tcl::mathfunc::long** to convert to a long integer \(that is,
acceptable to _Tcl\_GetLongFromObj_\).

 * keeping the **string is integer** command as it can be abbreviated to
   **string is int** to align with **::tcl::mathfunc::int**.

 * keeping the **string is wideinteger** command as it can be abbreviated to
   **string is wide** to align with **::tcl::mathfunc::wide**.

# Compatibility

On platforms where a **long_ variable has a different range than an **int**
variable, renaming the **::tcl::mathfunc::int** to **::tcl::mathfunc::long**
will let code like:

 \| set a [expr {int($b)}]

behave differently for **long** values outside the **int** range.

# Alternatives

The **bignum** was rejected in favor of **entier** because **entier** is
already used in **::tcl::mathfunc::entier**.

# Reference Implementation

Patches that implement the above, provide test cases for it, and update
documentation to include it are available at SourceForge as Tcl Patch
\#2581150<http://sourceforge.net/tracker2/?func=detail&aid=2581150&group_id=10894&atid=310894> .

# Copyright

This document has been placed in the public domain.

