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\DOC a
\TYPE {a : 'a -> 'a list -> 'a * 'a list}
\SYNOPSIS
Parser that requires a specific item.
\DESCRIBE
The call {a x} gives a parser that parses a single item that is exactly {x},
raising {Noparse} if the first item is something different.
\FAILURE
The call {a x} never fails, though the resulting parser may raise {Noparse}.
\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
++, |||, >>, atleast, elistof, finished, fix, leftbin, listof, many, nothing,
possibly, rightbin, some.
\ENDDOC
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