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.
- [det]help
- [det]help(+What)
- 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)
- Module
:Name - Give help on predicates with Name in Module and
any arity. Used for loaded code only.
- Module
:Name/Arity - Give help on predicates with Name in Module and Arity.
Used for loaded code only.
- 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.
help/1 shows
documentation from the manual as well as from loaded user code if the
code is documented using PlDoc. To show only the documentatoion of the
loaded predicate we may prefix predicate indicator with the module in
which it is defined.
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.
- [semidet,multifile]show_html_hook(+HTML:string)
- 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.
- [det]apropos(+Query)
- 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.
The library(explain) describes prolog-terms. The most
useful functionality is its cross-referencing function.
?- explain(subset(_,_)).
"subset(_, _)" is a compound term
from 2-th clause of lists:subset/2
Referenced from 46-th clause of prolog_xref:imported/3
Referenced from 68-th clause of prolog_xref:imported/3
lists:subset/2 is a predicate defined in
/staff/jan/lib/pl-5.6.17/library/lists.pl:307
Referenced from 2-th clause of lists:subset/2
Possibly referenced from 2-th clause of lists:subset/2
Note that PceEmacs can jump to definitions and gxref/0
can be used for an overview of dependencies.
- [det]explain(@Term)
- Give an explanation on Term. The argument may be any Prolog
data object. If the argument is an atom, a term of the form
Name/Arity
or a term of the form Module:Name/Arity, explain/1
describes the predicate as well as possible references to it. See also gxref/0.
- [nondet]explain(@Term,
-Explanation)
- True when Explanation is an explanation of Term.
The explaination is a list of elements that is printed using
print_message(information, explain(Explanation)).
