.TH "Fun" 3 2024-05-31 OCamldoc "OCaml library"
.SH NAME
Fun \- Function manipulation.
.SH Module
Module   Fun
.SH Documentation
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Module
.BI "Fun"
 : 
.B sig end

.sp
Function manipulation\&.

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.B "Since"
4.08

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.PP
.SS Combinators

.PP

.I val id 
: 
.B 'a -> 'a
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.ft B
id
.ft R
is the identity function\&. For any argument 
.ft B
x
.ft R
, 
.ft B
id x
.ft R
is 
.ft B
x
.ft R
\&.

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.I val const 
: 
.B 'a -> 'b -> 'a
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.ft B
const c
.ft R
is a function that always returns the value 
.ft B
c
.ft R
\&. For any
argument 
.ft B
x
.ft R
, 
.ft B
(const c) x
.ft R
is 
.ft B
c
.ft R
\&.

.sp

.I val compose 
: 
.B ('b -> 'c) -> ('a -> 'b) -> 'a -> 'c
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.ft B
compose f g
.ft R
is a function composition of applying 
.ft B
g
.ft R
then 
.ft B
f
.ft R
\&.
For any arguments 
.ft B
f
.ft R
, 
.ft B
g
.ft R
, and 
.ft B
x
.ft R
, 
.ft B
compose f g x
.ft R
is 
.ft B
f (g x)
.ft R
\&.

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.B "Since"
5.2

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.I val flip 
: 
.B ('a -> 'b -> 'c) -> 'b -> 'a -> 'c
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.ft B
flip f
.ft R
reverses the argument order of the binary function
.ft B
f
.ft R
\&. For any arguments 
.ft B
x
.ft R
and 
.ft B
y
.ft R
, 
.ft B
(flip f) x y
.ft R
is 
.ft B
f y x
.ft R
\&.

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.I val negate 
: 
.B ('a -> bool) -> 'a -> bool
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.ft B
negate p
.ft R
is the negation of the predicate function 
.ft B
p
.ft R
\&. For any
argument 
.ft B
x
.ft R
, 
.ft B
(negate p) x
.ft R
is 
.ft B
not (p x)
.ft R
\&.

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.PP
.SS Exception handling

.PP

.I val protect 
: 
.B finally:(unit -> unit) -> (unit -> 'a) -> 'a
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.ft B
protect ~finally work
.ft R
invokes 
.ft B
work ()
.ft R
and then 
.ft B
finally ()
.ft R
before 
.ft B
work ()
.ft R
returns with its value or an exception\&. In the
latter case the exception is re\-raised after 
.ft B
finally ()
.ft R
\&. If
.ft B
finally ()
.ft R
raises an exception, then the exception
.ft B
Fun\&.Finally_raised
.ft R
is raised instead\&.
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.ft B
protect
.ft R
can be used to enforce local invariants whether 
.ft B
work ()
.ft R
returns normally or raises an exception\&. However, it does not
protect against unexpected exceptions raised inside 
.ft B
finally ()
.ft R
such as 
.ft B
Out_of_memory
.ft R
, 
.ft B
Stack_overflow
.ft R
, or
asynchronous exceptions raised by signal handlers
(e\&.g\&. 
.ft B
Sys\&.Break
.ft R
)\&.
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Note: It is a programming error if other kinds of exceptions
are raised by 
.ft B
finally
.ft R
, as any exception raised in 
.ft B
work ()
.ft R
will
be lost in the event of a 
.ft B
Fun\&.Finally_raised
.ft R
exception\&. Therefore,
one should make sure to handle those inside the finally\&.

.sp

.I exception Finally_raised 
.B of 
.B exn

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.ft B
Finally_raised exn
.ft R
is raised by 
.ft B
protect ~finally work
.ft R
when
.ft B
finally
.ft R
raises an exception 
.ft B
exn
.ft R
\&. This exception denotes either
an unexpected exception or a programming error\&. As a general rule,
one should not catch a 
.ft B
Finally_raised
.ft R
exception except as part of
a catch\-all handler\&.

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