Re: how to invoke SML/NJ's built-in pretty printer from a program?

I don't think that what you want is possible in SML/NJ, since it  =

requires
runtime type information.  In the REPL, we are able to pretty-print  =

results
because we know their type, but that is not true in general.  Sorry.

	- John

On Feb 26, 2009, at 7:10 AM, Joe Wells wrote:

> SML/NJ has a built-in pretty printer for printing values of various
> types used by the top-level REPL.
>
> How do I invoke it from a program?
>
> There is a function PrettyPrint.pp_to_string of type int -> (stream ->
> 'a -> unit) -> 'a -> string, but to use it I would have to give it a
> value of type (stream -> 'a -> unit).  How do I construct this
> argument?
>
> To make my question concrete, in the following SML program, by what do
> I replace =93magic_pretty_printer=94 to make the program print =93Happy,
> happy, joy, joy!=94?
>
>  datatype Xyzzy =3D C of Xyzzy * Xyzzy | D of string
>
>  val plugh =3D C (D "hello",D "sailor")
>  val plugh_string =3D "C (D \"hello\",D \"sailor\")"
>
>  if ((magic_pretty_printer plugh) =3D plugh_string)
>     then (print "Happy, happy, joy, joy!\n")
>     else (raise (Fail "magic pretty printer gave wrong result"))
>
> I've browsed around the source for a while and failed to find what I
> need.  Any hints would be helpful.
>
> I'd rather not use Backend.Interact.evalStream and capture the output
> somehow, but if that is my only option I would be grateful for an
> example of how to do it.
>
> Thanks for your time in considering this question.
>
> -- =

> Joe
>
>
> -- =

> Heriot-Watt University is a Scottish charity
> registered under charity number SC000278.
>
>
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-OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise
-Strategies to boost innovation and cut costs with open source participation
-Receive a $600 discount off the registration fee with the source code: SFAD
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