f# - When executed will this be a tail call? -


once compiled , ran behave tail call?

let rec f accu = function    | [] -> accu    | h::t -> (h + accu) |> f <| t

maybe there easy way test behavior i'm not aware of, might question.

i think easier see if not use pipelining operator. in fact, 2 pipelining operators defined inline, compiler simplify code following (and think version more readable , simpler understand, write this):

let rec f accu = function    | [] -> accu    | h::t -> f (h + accu) t

now, can read definition of tail-call on wikipedia, says:

a tail call subroutine call happens inside procedure final action; may produce return value returned calling procedure.

so yes, call f on last line tail-call.

if wanted analyze original expression (h + accu) |> f <| t (without knowing pipelining operators inlined), becomes ((h + accu) |> f) <| t. means expression calls <| operator 2 arguments , returns result - call <| tail call.

the <| operator defined this:

let (<|) f = f

now, call f inside pipelining operator tail-call (and other pipelining operator).

in summary, if compiler did not inlining, have sequence of 3 tail-calls (compiled using .net .tail instruction make sure .net performs tail-call). however, since compiler performs inlining, see have recursive tail-call (f calling f) , can more efficiently compiled loop. (but calls across multiple functions or operators cannot use loops easily.)


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