Tips for golfing in OCaml

Question

Inspired from the assortment of other 'Tips for golfing in language xyz'. As usual, please only suggest tips that are specific to OCaml and not programming in general. One tip per answer please.

Answer 1

Use functions instead of match

let rec f=function[]->0|_::t->1+f t

is shorter than

let rec f x=match x with[]->0|_::t->1+f t

Answer 2

Never use begin [...] end

This:

begin [...] end 

is always synonymous with this:

([...])

Answer 3

Define several variables or functions at once

Thanks to tuples, you can define several variables at once. And as functions are first-class citizens...:

let f,g=(fun x->x+1),fun x->2*x

You can’t, however, write:

let f,g=(fun x->x+1),fun x->2*f x

Error: Unbound value f

Unfortunately, you can’t avoid the issue by using rec:

let rec f,g=(fun x->x+1),fun x->2*f x

Error: Only variables are allowed as left-hand side of let rec

Answer 4

Exploit curryied functions

Functions in OCaml are curryied. It might be useful to exploit that fact sometimes.

let n y=f x y

can be written

let n=f x

If you need arithmetic operations, you can surround them with parentheses so they behave like standard, prefix functions. (+), (-), ...

let n=(+)1;;
n 3;;

- : int = 4

Answer 5

downto

If you're not sure how to loop downwards, downto is usually the one to go for. Instead of:

for i=0 to 1000 do
Printf.printf"%d
"(1000-i)
done

You can do:

for i=1000 downto 0 do
Printf.printf"%d
"i
done

• Jo King: you could also do something like for i= -1000 to 0. Also, your syntax for these programs is missing the do done parts

Answer 6

print_string

Instead of the usual Printf.printf"", you can actually use the below (ONLY for strings, no formatting):

print_string"wassup"

Which is 1 byte shorter than:

Printf.printf"wassup"

• naffetS: Is this really worth a tip? It isn't normal to use Printf.printf for raw strings anyway