Nested stream cloptrs: unable to close over variables in scope

[aditya siram]

Hi,
I'm trying to take the cross product of two finite streams using nested 'cloptr' and I can't get it to typecheck, here's what I have:

fun foo(s:int): stream_vt(stream_vt(@(int,int))) =
  stream_vt_map_cloptr<int><stream_vt(@(int,int))>(
    streamize_intrange_lr(1,10),
    lam(i) =<cloptr1>
      stream_vt_map_cloptr<int><(int,int)>(
        streamize_intrange_lr(1,10),
        lam(j) =<cloptr1> @(i,j)
      )
  )

I want to cross (1..10) with (1..10) and get a stream of (1,1),(1,2),(1,3) ... but I get an error on the 'lam(j) =<cloptr1> @(i,j)' line:

...: dereference cannot be performed: the proof search for view located at [S2Evar(i(14251))] failed to turn up a result.
...: the dynamic expression cannot be assigned the type [S2Etyrec(flt0; npf=-1; 0=S2Ecst(int), 1=S2Ecst(int))].


The same thing works if instead of nesting a 'stream_vt_map_cloptr' I construct an explicit 'fun loop' inside the body of the first 'lam' that takes 'i' as an argument.

Why is there a difference?

[aditya siram]

But this typechecks and I don't understand why:

fun foo(s:int): stream_vt(stream_vt(@(int,int))) =
  stream_vt_map_cloptr<int><stream_vt(@(int,int))>(
    streamize_intrange_lr(1,10),
    lam(i) =<cloptr1>

      let
        val i = i (* added this *)
      in

        stream_vt_map_cloptr<int><(int,int)>(
          streamize_intrange_lr(1,10),
          lam(j) =<cloptr1> @(i,j)
        )

      end
  )

[aditya siram]

It also typechecks if I do '!i' instead of just 'i' so I guess it's passed in as a reference and needs to be dereferenced before passing it along:

fun foo(s:int): stream_vt(stream_vt(@(int,int))) =
  stream_vt_map_cloptr<int><stream_vt(@(int,int))>(
    streamize_intrange_lr(1,10),
    lam(i) =<cloptr1>
      stream_vt_map_cloptr<int><(int,int)>(
        streamize_intrange_lr(1,10),

        lam(j) =<cloptr1> @(!i,j)
      )
  )

But in this example I didn't need to deference 'i' before adding to it:

fun bar(s:int): stream_vt(int) =
  stream_vt_map_cloptr<int><int>(
    streamize_intrange_lr(1,10),
    lam(i) =<cloptr1> i+1
  )

So while I've solved my original problem I still don't know why it works.

[aditya siram]

Actually that last example where I used '!i' doesn't work but the previous one where I did 'let val i = i in ... end' does.

Sorry for the noise.

[gmhwxi]

In the following code, 'i' is passed as a reference, which cannot be

used under another 'lam':

lam(i) =<cloptr1>
      stream_vt_map_cloptr<int><(int,int)>(
        streamize_intrange_lr(1,10),

        lam(j) =<cloptr1> @(!i,j)
      )

You need to do 'let val i = i ...' to take out the value stored in the original 'i'

so that you can have access to it under another 'lam'.