Pragmatic directives
Pragmatic directives cause the language to operate in a specific manner, allowing support for operational variances within the program code (possibly by the loading of specific or alternative modules).
The task is to list any pragmatic directives supported by the language, demostrate how to activate and deactivate the pragmatic directives and to describe or demonstate the scope of effect that the pragmatic directives have within a program.
BASIC
Some versions of basic support the use of system trace directives that allow the program line or line number to be output.
<lang basic>10 TRON: REM activate system trace pragma 20 TROFF: REM deactivate system trace pragma</lang>
Perl
By convention pragmatic modules are named using lowercase letters.
- List of pragmatic modules
- diagnostics
- english
- feature
- integer
- lib
- ops
- sort
- strict
- switch
- warnings
- Utilization
Pragmatic modules have local scope and are utilized using the use directive:
<lang perl>use warnings; # use warnings pragma module use strict; # use strict pragma module</lang>
To disable behaviour of a pragmatic module:
<lang perl>no warnings; # disable warnings pragma module no strict; # disable strict pragma module</lang>
PicoLisp
PicoLisp makes no formal difference between any normal and "specific" operation of the language. Any possible desired effect can be achieved by calling a function or setting a variable. For example, function calls can be traced with the 'trace' function.
Python
Python has the __future__ module which controls certain features:
- Python 3.2
<lang python>Python 3.2 (r32:88445, Feb 20 2011, 21:30:00) [MSC v.1500 64 bit (AMD64)] on win32 Type "copyright", "credits" or "license()" for more information. >>> import __future__ >>> __future__.all_feature_names ['nested_scopes', 'generators', 'division', 'absolute_import', 'with_statement', 'print_function', 'unicode_literals', 'barry_as_FLUFL'] >>> </lang>
('barry_as_FLUFL' is an April fools joke)
- Python 2.7
<lang python>Python 2.7.2 (default, Jun 12 2011, 14:24:46) [MSC v.1500 64 bit (AMD64)] on win32 Type "copyright", "credits" or "license()" for more information. >>> import __future__ >>> __future__.all_feature_names ['nested_scopes', 'generators', 'division', 'absolute_import', 'with_statement', 'print_function', 'unicode_literals'] >>> </lang>
UNIX Shell
- List of pragmatic directives
- -v output the script line before it is executed
- -x output the command line arguments
- Utilization
Pragmatic directives remain effective, until they are deactivated, or the end of the script is reached:
<lang sh>set -vx # Activate both script line output and command line arguments pragma set +vx # Deactivate both pragmatic directives</lang>