module Lazy:sig
..end
'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.
type'a
t ='a lazy_t
include Monad.S
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
except that 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.val t_of_sexp : (Sexplib.Sexp.t -> 'a) -> Sexplib.Sexp.t -> 'a t
val sexp_of_t : ('a -> Sexplib.Sexp.t) -> 'a t -> Sexplib.Sexp.t
val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
val bin_t : 'a Bin_prot.Type_class.t -> 'a t Bin_prot.Type_class.t
val bin_read_t : 'a Bin_prot.Unsafe_read_c.reader -> 'a t Bin_prot.Read_ml.reader
val bin_read_t_ : 'a Bin_prot.Unsafe_read_c.reader ->
'a t Bin_prot.Unsafe_read_c.reader
val bin_read_t__ : 'a Bin_prot.Unsafe_read_c.reader ->
(int -> 'a t) Bin_prot.Unsafe_read_c.reader
val bin_reader_t : 'a Bin_prot.Type_class.reader -> 'a t Bin_prot.Type_class.reader
val bin_size_t : 'a Bin_prot.Size.sizer -> 'a t Bin_prot.Size.sizer
val bin_write_t : 'a Bin_prot.Unsafe_write_c.writer -> 'a t Bin_prot.Write_ml.writer
val bin_write_t_ : 'a Bin_prot.Unsafe_write_c.writer ->
'a t Bin_prot.Unsafe_write_c.writer
val bin_writer_t : 'a Bin_prot.Type_class.writer -> 'a t Bin_prot.Type_class.writer
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.force
except that if the computation of x
raises an exception, it is
unspecified whether force_val x
raises the same exception or Undefined
.lazy_from_fun f
is the same as lazy (f ())
but slightly more
efficient.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)
.lazy_is_val x
returns true
if x
has already been forced and
did not raise an exception.