help.pl -- Text based manual

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.

help is det

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.

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.

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.

Re-exported predicates

The following predicates are exported from this file while their implementation is defined in imported modules or non-module files loaded by this module.