Module Fmlib_std.List

A thin wrapper around Stdlib.List which avoids throwing exceptions and with some additional monadic functions.

In case you need functions from the module List of the ocaml standard library, just use Stdlib.List

List Monad

type 'a t = 'a list

A list of values of type 'a.

val return : 'a -> 'a t

return a makes a singleton list with the element a.

val (>>=) : 'a t -> ('a -> 'b t) -> 'b t

l >>= f applies the function f to all elements of the list l and concatenates all lists.

val let* : 'a t -> ('a -> 'b t) -> 'b t

let* a = m in f a is equivalent to m >>= f.

val (>=>) : ('a -> 'b t) -> ('b -> 'c t) -> 'a -> 'c t

f >=> g composes the two monadic functions f and g.

val (<*>) : ('a -> 'b) t -> 'a t -> 'b t

flst <*> lst is equivalent to flst >>= fun f -> map f lst i.e. it maps all functions contained in flst over the list lst and then concatenates the results.

val join : 'a list list -> 'a list

join is the same as concat.

Modified list functions

val find : ('a -> bool) -> 'a t -> 'a option

find p l finds an element e in the list l which satisfies p e.

List functions from Stdlib

val append : 'a list -> 'a list -> 'a list

append a b concatenate the lists a and b.

Synonym a @ b.

val concat : 'a list list -> 'a list

concat ll concatenates all lists contained in the list of lists ll.

val split : ('a * 'b) list -> 'a list * 'b list

Transform a list of pairs into a pair of lists.

val rev : 'a list -> 'a list

rev a reverses the list a.

val rev_append : 'a list -> 'a list -> 'a list

rev_append a b prepends the lists rev a in front of the list b.

val length : 'a t -> int

length l The length of the list l.

val filter : ('a -> bool) -> 'a t -> 'a t

filter p l Returns a list with all the elements of l which satisfy the predicate p.

val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a

fold_left f s l

Compute f (f ... (f a b1) ... bn-1) bn where l = [b1; ...; bn-1; bn]

val fold_right : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b

like fold_left, just iterate from right to left.

val map : ('a -> 'b) -> 'a list -> 'b list

map f l returns a list where all elements of l are mapped by the function f.

val mapi : (int -> 'a -> 'b) -> 'a list -> 'b list

mapi f l map all elements of the list l with the mapping function f which receives the index of the element (starting at zero) and the element.

val rev_map : ('a -> 'b) -> 'a list -> 'b list

rev_map f l The same as map (rev l). rev_map is tail recursive.

val for_all : ('a -> bool) -> 'a list -> bool

for_all p l checks, if all elements in the list l satisfy the predicate p.

val exists : ('a -> bool) -> 'a list -> bool

exists p l checks, if some element in the list l satisfies the predicate p.

Additional list functions

val split_head_tail : 'a t -> 'a * 'a t

split_head_tail l split the list in its head and tail part.

Precondition: The list is not empty.

val map_and_filter : ('a -> 'b option) -> 'a list -> 'b list

map_and_filter f list maps the list with f and removes the element for which f e = None.

val split_at : ('a -> bool) -> 'a t -> 'a t * 'a t

split_at p lst scans the list until it finds the first element satisfying p and returns the prefix and the remainder starting at the encountered element. If the second list is empty, then there is no element in the list satisfying p.

val transpose : 'a list list -> 'a list list

transpose list_of_rows returns the list of columns.


  • The list of rows must not be empty.
  • All rows in the list of rows must not be empty and have the same length.


transpose [ [1; 2; 3]; [4; 5; 6] ]
[ [1; 4]; [2; 5]; [3; 6] ]

Monadic list functions

module Monadic : functor (M : Interfaces.MONAD) -> sig ... end

Monadic list functions