This plugin defines a command |:TAssert| that takes an expression as 
argument and throws an exception if this expression evaluates to 
|empty()|. You can insert these comments throughout your code whenever 
something could potentially go wrong. The exception is then thrown right 
where the problem occurs. You could think of it as a poor man's 
design-by-contract substitute.

One goal of this plugin is to allow users to quickly switch on or off 
assertions depending on the context. This can be done either by:

    1. Turning assertions off so that they are not evaluated. This can 
       be achieved by setting g:TASSERT to 0 or by calling the command 
       |:TAssertOff|.

    2. Commenting out assertions in the current buffer by calling the 
       commmand |:TAssertComment|.


Example: >

    fun! Test(a, b)
        TAssertType a:a, 'string'
        TAssertType a:b, 'number'
        TAssert !empty(a:a)
        return repeat(a:a, a:b)
    endf

NOTE: The |:TAssertType| command requires the spec.vim plugin.


                                                    *tAssert-logging*
Logging:~

TAssert also includes a few convenience commands for logging -- see 
|:TLog|.

                                                    *g:TLOG*
The variable g:TLOG controls where messages are written to:

    echom ... Print messages in the echo area.
    file  ... Print messages to a file; syntax "file:FILENAME"
    Decho ... Print messages via Decho (vimscript#642)


                                                    *tAssert-install*
Install:~

Edit the vba file and type: >

    :so %

See :help vimball for details. If you have difficulties or use vim 7.0, 
please make sure, you have the current version of vimball (vimscript 
#1502) installed.

See also |tassert-macros|.


                                                    *tAssert-redistribute*
Compatibility:~

If you want to redistribute files containing assertions but don't want 
to have people install this plugin, insert this close to the top of 
your file: >

    if !exists(':TAssert')
        command! -nargs=* -bar -bang TAssert :
        command! -nargs=* -bar -bang TAssertType :
    endif

Alternatively, use the |:TAssertComment| command.


%s


Status:  Works for me (there may be some minor quirks)
Install: See http://github.com/tomtom/vimtlib/blob/master/INSTALL.TXT
See http://github.com/tomtom for related plugins.