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GNU/Linux |
Debian 7.3.0(Wheezy) |
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Lazy(3o) |
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Lazy − Deferred computations.
Module Lazy
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 suspension, 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(lazy(...(lazy 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 −rectypes 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 lazy_from_fun : (unit -> ’a) -> ’a t
lazy_from_fun f is the same as lazy (f ()) but slightly more efficient.
val lazy_from_val : ’a -> ’a t
lazy_from_val v returns an already−forced suspension of v This is for special purposes only and should not be confused with lazy (v) .
val lazy_is_val : ’a t -> bool
lazy_is_val x returns true if x has already been forced and did not raise an exception.
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Lazy(3o) | |