So, I'm trying to write code like (simplifying):
let my_output (_: string) = ();; (* the real code is much more
complicated but not relevant *)
let foo b fmt =
if not b then
Printf.ifprintf () fmt
else
Printf.ksprintf my_output fmt
;;
The problem is that the above code doesn't compile- ifprintf wants fmt
to be ('b, unit, unit) format = ('b, unit, unit, unit) format4, while
ksprintf wants it to be ('b, unit, string, 'a) format4. Now, I could do
the above like:
let foo b fmt =
Printf.ksprintf (fun s -> if b then my_output s) fmt
but the point and purpose of using ifprintf is to avoid the cost of
converting the arguments to strings that are just going to be thrown away.
So, my questions are:
1: is there a way to make this work without using Obj.magic or
rewritting isprintf?
2: is there a reason ifprintf has the type 'a -> ('b, 'a, unit) format
-> 'b, instead of ('b, 'a, 'c) format -> 'b, or better yet ('b, 'a, 'c,
'd) format4 -> 'b, or even better yet ('b, 'a, 'c, 'd, 'e, 'f) format6
-> 'b (allowing it to unify with more different formats)?
3: Does ifprintf actually avoid the cost of converting it's arguments to
strings? The code is unclear. If the answer to this is 'no', the other
two questions are moot.
Brian
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