id is the identity function. For any argument x, id x is x.

const c is a function that always returns the value c. For any argument x, (const c) x is c.

flip f reverses the argument order of the binary function f. For any arguments x and y, (flip f) x y is f y x.

negate p is the negation of the predicate function p. For any argument x, (negate p) x is not (p x).

protect ~finally work invokes work () and then finally () before work () returns with its value or an exception. In the latter case the exception is re-raised after finally (). If finally () raises an exception, then the exception Finally_raised is raised instead.

protect can be used to enforce local invariants whether work () returns normally or raises an exception. However, it does not protect against unexpected exceptions raised inside finally () such as Stdlib.Out_of_memory, Stdlib.Stack_overflow, or asynchronous exceptions raised by signal handlers (e.g. Sys.Break).

Note: It is a programming error if other kinds of exceptions are raised by finally, as any exception raised in work () will be lost in the event of a Finally_raised exception. Therefore, one should make sure to handle those inside the finally.

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

and_p f g x is (f x) && (g x). Produces a predicate which is a conjunction of the two predicates.

• since 3.13.1

or_p f g x is (f x) || (g x). Produces a predicate which is a disjunction of the two predicates.

• since 3.13.1

compose f g x is g (f x). Composition.

compose_binop f g is fun x y -> g (f x) (f y). Example (partial order): List.sort (compose_binop fst CCInt.compare) [1, true; 2, false; 1, false].

• since 0.6

curry f x y is f (x,y). Convert a function which accepts a pair of arguments into a function which accepts two arguments.

uncurry f (x,y) is f x y. Convert a function which accepts a two arguments into a function which accepts a pair of arguments.

tap f x evaluates f x, discards it, then returns x. Useful in a pipeline, for instance:

CCArray.(1 -- 10)
  |> tap CCArray.shuffle
  |> tap @@ CCArray.sort Stdlib.compare

Lexicographic combination of comparison functions.

finally ~h f calls f () and returns its result. If it raises, the same exception is raised; in any case, h () is called after f () terminates. If h () raises an exception, then this exception will be passed on and any exception that may have been raised by f () is lost.

finally1 ~h f x is the same as f x, but after the computation, h () is called whether f x rose an exception or not. If h () raises an exception, then this exception will be passed on and any exception that may have been raised by f () is lost.

• since 0.16

finally2 ~h f x y is the same as f x y, but after the computation, h () is called whether f x y rose an exception or not. If h () raises an exception, then this exception will be passed on and any exception that may have been raised by f () is lost.

• since 0.16

opaque_identity x is like x, but prevents Flambda from using x's definition for optimizing it. (flambda is an optimization/inlining pass in OCaml >= 4.03).

• since 0.18

iterate n f is f iterated n times. That is to say, iterate 0 f x is x, iterate 1 f x is f x, iterate 2 f x is f (f x), etc.

• since 2.1

with_return f is f return, where return is a function that can be invoked to exit the scope early.

For example:

let find_array arr x =
  let@ return = with_return in
  for i = 0 to Array.length arr-1 do
    if arr.(i) = x then return i;
  done;
  -1

• since 3.15