Comment author: administrator

It would be nice to have the ability to create functions akin to
Printf.sprintf
which take multiple arguments, and do something with the resulting string.

This is already done in the current working version of ocaml, although not
exactly with the same type that you are suggesting:

val kprintf : (string -> string) -> ('a, unit, string) format -> 'a
(** [kprintf k format arguments] is the same as [sprintf format arguments],
except that the resulting string is passed as argument to [k]; the
result of [k] is then returned as the result of [kprintf]. *)

Thanks for the suggestion,

-- Damien

Comment author: administrator

Damien Doligez wrote:

This is already done in the current working version of ocaml, although not
exactly with the same type that you are suggesting:

val kprintf : (string -> string) -> ('a, unit, string) format -> 'a
(** [kprintf k format arguments] is the same as [sprintf format arguments],
except that the resulting string is passed as argument to [k]; the
result of [k] is then returned as the result of [kprintf]. *)

Maybe one day I will come up with an original idea!
This does help me in that I no longer need
a separate copy of printf.ml, but it means any function
I create utilising kprintf will return a string, even if
it is side effecting. No choice! Is there any reason why the
continuation cannot be a general consumer of arbitrary
return type?

A slight amendment to the type I proposed (I think the
3rd arg to the format constructor is meant to reflect
the overall return type?)val kprintf : (string -> 'a) -> ('b, unit, 'a) format -> 'b

Cheers,
chris

Comment author: administrator

val kprintf : (string -> 'a) -> ('b, unit, 'a) format -> 'b

This is exactly what I tried at first, but it doesn't work with %a
and %t formats: the typing of these formats is not general enough
to support this version.

Consider this piece of code: kprintf outfun "%a" fmtfun argument
The typing of formats constrains the result of fmtfun to be the same
as 'a (the final result of kprintf). But the result of fmtfun has to be
a string (because kprintf is in fact sprintf in disguise) so 'a has to
be string.

The proper solution would be to add a fourth argument to the "format"
type constructor, but the current solution is good enough and does not
break compatibility with previous versions.

-- Damien