Lazy(3) OCaml library Lazy(3)
NAME
Lazy - Deferred computations.
Module
Module Lazy
Documentation
Module Lazy
: sig end
Deferred computations.
type 'a t = 'a lazy_t
A value of type 'a Lazy.t is a deferred computation, called a suspen-
sion, that has a result of type 'a . The special expression syntax
lazy (expr) makes a suspension of the computation of expr , without
computing expr itself yet. "Forcing" the suspension will then compute
expr and return its result.
Note: lazy_t is the built-in type constructor used by the compiler for
the lazy keyword. You should not use it directly. Always use Lazy.t
instead.
Note: Lazy.force is not thread-safe. If you use this module in a
multi-threaded program, you will need to add some locks.
Note: if the program is compiled with the -rectypes option, ill-founded
recursive definitions of the form let rec x = lazy x or let rec x =
Lazy(3) x))) are accepted by the type-checker and lead, when
forced, to ill-formed values that trigger infinite loops in the garbage
collector and other parts of the run-time system. Without the -rec-
types option, such ill-founded recursive definitions are rejected by
the type-checker.
exception Undefined
val force : 'a t -> 'a
force x forces the suspension x and returns its result. If x has
already been forced, Lazy.force x returns the same value again without
recomputing it. If it raised an exception, the same exception is
raised again. Raise Undefined if the forcing of x tries to force x
itself recursively.
val force_val : 'a t -> 'a
force_val x forces the suspension x and returns its result. If x has
already been forced, force_val x returns the same value again without
recomputing it. Raise Undefined if the forcing of x tries to force x
itself recursively. If the computation of x raises an exception, it is
unspecified whether force_val x raises the same exception or Undefined
.
val from_fun : (unit -> 'a) -> 'a t
from_fun f is the same as lazy (f ()) but slightly more efficient.
Since 4.00.0
val from_val : 'a -> 'a t
from_val v returns an already-forced suspension of v . This is for
special purposes only and should not be confused with lazy (v) .
Since 4.00.0
val is_val : 'a t -> bool
is_val x returns true if x has already been forced and did not raise an
exception.
Since 4.00.0
val lazy_from_fun : (unit -> 'a) -> 'a t
Deprecated. synonym for from_fun .
val lazy_from_val : 'a -> 'a t
Deprecated. synonym for from_val .
val lazy_is_val : 'a t -> bool
Deprecated. synonym for is_val .
OCamldoc 2014-10-18 Lazy(3)
ocaml 4.02.1 - Generated Sun Oct 19 12:51:09 CDT 2014