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Pack onepointfour_basics -- prolog/doc/README_stringy_justify.md



  • ../stringy_justify.pl (MIT license)
  • [stringy_justify.plt](../stringy_justify.plt) (0BSD license) Justify strings inside a field of given width supposed to contain only SPACE (ASCII 0x20) characters.

Loading the module and running its tests (in SWI-Prolog)

Please refer to the README.md file, but in short:

?- assertz(file_search_path(library,'/foo/bar/prolog_code/unpacked')).
?- use_module(library('onepointfour_basics/stringy_justify.pl')).
?- load_test_files([]).
?- run_tests.



One always wants to justify Text (a "stringy", i.e. an atom or string) inside a field of Width SPACE characters, giving Result. Result can also be passed instantiated in case one wants to "accept" Result instead of generating it. The actual type of the Result is given by ResultType: one of the atoms atom or string.

The resulting text will always be of Width (>= 0) with the SPACE character doing required padding. Text that overflows out of the field of Width SPACE is cut off by default, but that can be configured.

A variation on the above is:


which allows you to specify how to justifiy via a parameter instead of via the functor name: Set How to one of left, right, center.

For finetuning, there are predicates which take an additional SettingDict SWI-Prolog dict:


The following key-value pairs are recognized:

cut_lefttrue, falsetrueCut off overflowing text on the left
cut_righttrue, falsetrueCut off overflowing text on the right
offsetinteger0Additional padding to be added (or subtracted) on the left in case of "left" justification, and to be added (or subtracted) on the right in case of "right" justification
offset_leftinteger0Additional padding to be added (or subtracted) on the left in case of "center" justification
offset_rightinteger0Additional padding to be added (or subtracted) on the right in case of "center" justification
preferrightly, leftlyleftlyIn the case of center justification, there may be amibuity as to whether to shift the text to the left or to the right by a single character. This setting influences the decision. Esoteric.


?- justify_how(right,10,"hello",Result,string).
Result = "     hello".
?- justify_how(left,10,"hello",Result,string).
Result = "hello     ".
?- justify_how(center,10,"hello",Result,string).
Result = "  hello   ".
?- justify_how(right,10,"hello",Result,string,_{offset:3}).
Result = "  hello   ".
?- justify_how(right,15,"hello",Result,string,_{offset:3}).
Result = "       hello   ".
?- justify_how(right,15,"hello world this is a long text",Result,string,_{offset:3}).
Result = " a long text   ".