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\DOC possibly
\TYPE {possibly : ('a -> 'b * 'a) -> 'a -> 'b list * 'a}
\SYNOPSIS
Attempts to parse, returning empty list of items in case of failure.
\DESCRIBE
If {p} is a parser, then {possibly p} is another parser that attempts to parse
with {p} and if successful returns the result as a singleton list, but will
return the empty list instead if the core parser {p} raises {Noparse}.
\FAILURE
Never fails.
\COMMENTS
This is one of a suite of combinators for manipulating ``parsers''. A parser is
simply a function whose OCaml type is some instance of
{:('a)list -> 'b * ('a)list}. The function should take a list of objects of
type {:'a} (e.g. characters or tokens), parse as much of it as possible from
left to right, and return a pair consisting of the object derived from parsing
(e.g. a term or a special syntax tree) and the list of elements that were not
processed.
\SEEALSO
++, ||, >>, a, atleast, elistof, finished, fix, leftbin, listof, many, nothing,
rightbin, some.
\ENDDOC
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