Using a stack allocated tuple as an enviroment

[aditya siram]

Hi,
I'm trying to pass and mutate a stack allocated tuple in a string processing function:

fn length_last
  {l:nat | l > 1 }
  (
    s: string l
  ): (int, char) =
  let
    var env = (0,s.head())
    implement stream_vt_foreach$fwork<charNZ><(int,charNZ)>(c,env) =
      env := (env.0 + 1, c)
    val _ = stream_vt_foreach_env(
              streamize_string_char(s.tail()),
              env
            )
  in
   env
  end

 The stack allocated 'env' should finally have the length of the string and the last character after 'stream_vt_foreach_env' is run. Instead I get compile errors like:

length_last.dats:15:13: the dynamic expression should be a left-value but it is not.

length_last.dats:11:3: the linear dynamic variable [env$view$5548(-1)] is preserved but with an incompatible type.

length_last.dats:11:3: mismatch of static terms (tyleq):

The actual term is: S2Etop(knd=0; [1])
[1]: S2EVar(5260)
The needed term is: S2Etyrec(flt0; npf=-1; 0=S2Etop(knd=0; S2Etop(knd=0; [1])), 1=S2Etop(knd=0; S2Etop(knd=0; [2])))
[1]: g1int_int_t0ype(int_kind, 0)
[2]: charNZ

length_last.dats:11:3: mismatch of static terms (tyleq):

The actual term is: S2Eat(S2Etop(knd=0; [1]); [2])
[1]: S2EVar(5260)
[2]: env
The needed term is: S2Eat(S2Etyrec(flt0; npf=-1; 0=S2Etop(knd=0; S2Etop(knd=0; [1])), 1=S2Etop(knd=0; S2Etop(knd=0; [2]))); [3])
[1]: g1int_int_t0ype(int_kind, 0)
[2]: charNZ
[3]: env
patsopt(TRANS3): there are [2] errors in total.
exit(ATS): uncaught exception: _2home_2deech_2Downloads_2ATS_2ATS2_2src_2pats_error_2esats__FatalErrorExn(1025)

Is the problem that I'm passing a stack allocated tuple as the environment?

Thanks!

[Hongwei Xi]

This is the best I could come up with.

Mixing templates with dependent types almost always

causes problems.

(* ****** ****** *)

//
#include
"share/atspre_staload.hats"
//

fn
length_last
{l:nat | l > 1 }
(
 s: string l
) : (int, char) = let

  typedef tenv = (int, char)
  var env: tenv = (0,s.head())
  implement
  stream_vt_foreach$fwork<char><tenv>(c,env) = env := (env.0 + 1, c)
  val-~stream_vt_nil() =
    stream_vt_foreach_env<char><tenv>(streamize_string_char(s.tail()), env)
in
  env
end

implement
main0() = let
val
tup =
length_last("abcde")
in
println! ("(", tup.0, ", ", tup.1, ")")
end // end of [main0]

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[aditya siram]

Oh, thanks!

So if I wanted to return '(int, charNZ)' instead I'd need some kind of 'praxi' asserting that it's not null?

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[Hongwei Xi]

I changed char to charNZ, and it actually worked!

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[aditya siram]

Ah, very nice. So the moral seems to be to fully annotate all template functions.

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