This chapter describes syntactic extensions and convenience features
that are implemented in Objective Caml, but not described in the
Objective Caml reference manual.
||Streams and stream parsers
Streams and stream parsers are no longer part of the Objective Caml
language, but available through a CamlP4 syntax extension. See the
CamlP4 reference manual for more information. Objective Caml programs
that use streams and stream parsers can be compiled with the
-pp camlp4o option to ocamlc and ocamlopt. For interactive use,
run ocaml and issue the
#load "camlp4o.cma";; command.
In patterns, Objective Caml recognizes the form
' c ' .. ' d '
(two character literals separated by ..) as shorthand for the pattern
' c ' | ' c1 ' | ' c2 ' | ...
| ' cn ' | ' d '
where c1, c2, ..., cn are the characters
that occur between c and d in the ASCII character set. For
instance, the pattern '0'..'9' matches all characters that are digits.
Objective Caml supports the assert construct to check debugging assertions.
The expression assert expr evaluates the expression expr and
returns () if expr evaluates to true. Otherwise, the exception
Assert_failure is raised with the source file name and the
location of expr as arguments. Assertion
checking can be turned off with the -noassert compiler option.
As a special case, assert false is reduced to
raise (Assert_failure ...), which is polymorphic (and
is not turned off by the -noassert option).
The expression lazy expr returns a value v of type Lazy.t that
encapsulates the computation of expr. The argument expr is not
evaluated at this point in the program. Instead, its evaluation will
be performed the first time Lazy.force is applied to the value
v, returning the actual value of expr. Subsequent applications
of Lazy.force to v do not evaluate expr again.
For more information, see the description of module Lazy in the
let module module-name = module-expr in expr
locally binds the module expression module-expr to the identifier
module-name during the evaluation of the expression expr.
It then returns the value of expr. For example:
let remove_duplicates comparison_fun string_list =
let module StringSet =
Set.Make(struct type t = string
let compare = comparison_fun end) in
(List.fold_right StringSet.add string_list StringSet.empty)
||Grouping in integer and floating-point literals
In integer and floating-point literals, the character _ (underscore)
can be used to separate groups of digits, as in 1_000_000,
0x45_FF, or 1_234.567_89. The underscore characters are simply
ignored when reading the literal.