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help.pl -- Text based manual
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This module provides help/1 and apropos/1 that give help on a topic or searches the manual for relevant topics.

By default the result of help/1 is sent through a pager such as less. This behaviour is controlled by the following:

  • The Prolog flag help_pager, which can be set to one of the following values:
    false
    Never use a pager.
    default
    Use default behaviour. This tries to determine whether Prolog is running interactively in an environment that allows for a pager. If so it examines the environment variable PAGER or otherwise tries to find the less program.
    Callable
    A Callable term is interpreted as program_name(Arg, ...). For example, less('-r') would be the default. Note that the program name can be an absolute path if single quotes are used.
Source help is det
Source help(+What) is det
Show help for What. What is a term that describes the topics(s) to give help for. Notations for What are:
Atom
This ambiguous form is most commonly used and shows all matching documents. For example:
?- help(append).
Name / Arity
Give help on predicates with matching Name/Arity. Arity may be unbound.
Name // Arity
Give help on the matching DCG rule (non-terminal)
f(Name/Arity)
Give help on the matching Prolog arithmetic functions.
c(Name)
Give help on the matching C interface function
section(Label)
Show the section from the manual with matching Label.

If an exact match fails this predicates attempts fuzzy matching and, when successful, display the results headed by a warning that the matches are based on fuzzy matching.

If possible, the results are sent through a pager such as the less program. This behaviour is controlled by the Prolog flag help_pager. See section level documentation.

See also
- apropos/1 for searching the manual names and summaries.
Source show_html_hook(+HTML:string) is semidet[multifile]
Hook called to display the extracted HTML document. If this hook fails the HTML is rendered to the console as plain text using html_text/2.
Source apropos(+Query) is det
Print objects from the manual whose name or summary match with Query. Query takes one of the following forms:
Type:Text
Find objects matching Text and filter the results by Type. Type matching is a case intensitive prefix match. Defined types are section, cfunction, function, iso_predicate, swi_builtin_predicate, library_predicate, dcg and aliases chapter, arithmetic, c_function, predicate, nonterminal and non_terminal. For example:
?- apropos(c:close).
?- apropos(f:min).
Text
Text is broken into tokens. A topic matches if all tokens appear in the name or summary of the topic. Matching is case insensitive. Results are ordered depending on the quality of the match.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

Source help(Arg1)