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package travesty
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Function combinator extensions for Core_kernel.

This just re-exports Travesty_base_exts.Alist, but may contain Core_kernel-specific extensions in future.

include module type of Travesty_base_exts.Fn

Constant predicates

These are convenience shorthands for Base.Fn.const.

val always : 'a -> bool

always x is true.

val never : 'a -> bool

never x is false.

Pointwise liftings of operators

These complement Base.Fn.non.

val conj : ('a -> bool) -> ('a -> bool) -> 'a -> bool

conj f g lifts && over predicates f and g. It is short-circuiting: g is never called if f returns false.

Examples:

let is_zero = Int.(conj is_non_negative is_non_positive)
(* Short-circuiting: *)
conj always (fun () -> failwith "oops") (); (* --> exception *)
conj never  (fun () -> failwith "oops") (); (* --> false *)
val disj : ('a -> bool) -> ('a -> bool) -> 'a -> bool

disj f g lifts || over predicates f and g. It is short-circuiting: g is never called if f returns true.

Examples:

let is_not_zero = Int.(disj is_negative is_positive)
(* Short-circuiting: *)
disj never  (fun () -> failwith "oops") (); (* --> exception *)
disj always (fun () -> failwith "oops") (); (* --> false *)
val (&&&) : ('a -> bool) -> ('a -> bool) -> 'a -> bool

f &&& g is conj f g.

val (|||) : ('a -> bool) -> ('a -> bool) -> 'a -> bool

f ||| g is disj f g.

Miscellaneous combinators

val on : ('a -> 'b) -> 'a -> 'a -> f:('b -> 'b -> 'r) -> 'r

on lift x y ~f lifts a binary function f using the lifter lift. It does the same thing as the `on` function from Haskell, but with arguments flipped to make sense without infixing.

Effectively, it's Base.Comparable.lift, but with a slightly different signature.

Example:

let ints = on fst    ~f:Int.equal (42, "banana") (42, "apple") in
let strs = on snd ~f:String.equal (42, "banana") (42, "apple") in
ints, strs (* --> true, false *)