"ocaml_beginners"::[] Bigarray.Array1.map_file - can't automatically allocate array

Can't seem to get to grips with Bigarray.Array1.map_file,
and I can't
find any examples online. I'm trying to pass in -1 for the
filesize
(which, according to the docs, is supposed to automatically
allocate
an array equal to the size of the file) but it fails in the
compile
stage with

 $ cat dawgutils.ml
open Bigarray
open Printf

let dawg =
  let fd = Unix.openfile "sowpods.dwg" [
Unix.O_RDONLY ] 0 in
  Array1.map_file fd int32 c_layout false -1;;

$ ocaml unix.cma bigarray.cma dawgutils.ml
File "dawgutils.ml", line 6, characters 2-41:
This expression has type
  int -> (int32, Bigarray.int32_elt, Bigarray.c_layout)
Bigarray.Array1.t
but is here used with type int

martin


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On Sat, 12 Aug 2006, "Martin DeMello"
<martindemellogmail.com> wrote:
> 
> let dawg =
>   let fd = Unix.openfile "sowpods.dwg" [
Unix.O_RDONLY ] 0 in
>   Array1.map_file fd int32 c_layout false -1;;

Try this:

  Array1.map_file fd int32 c_layout false (-1)

(otherise "-" is taken as a binary operator).

ChriS


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On Aug 11, 2006, at 1:04 PM, Martin DeMello wrote:

> let dawg =
>   let fd = Unix.openfile "sowpods.dwg" [
Unix.O_RDONLY ] 0 in
>   Array1.map_file fd int32 c_layout false -1;;
>
> $ ocaml unix.cma bigarray.cma dawgutils.ml
> File "dawgutils.ml", line 6, characters
2-41:
> This expression has type
>   int -> (int32, Bigarray.int32_elt,
Bigarray.c_layout)  
> Bigarray.Array1.t
> but is here used with type int

It looks like the compiler might be parsing that as:
(Array1.map_file fd int32 c_layout false) - 1;;

Changing -1 to ~-1 using the explicit unary negative works
fine.

William D. Neumann

"I eat T-bone steaks, I lift barbell plates, I'm
sweeter than a
German chocolate cake. I'm the reflection of perfection,
the number
one selection. I'm the man of the hour, the man with the
power, too
sweet to be sour. The ladies' pet, the men's regret, where
what you
see is what you get, and what you don't see, is better
yet."

          --Superstar Billy Graham





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On 8/12/06, William Neumann <wneumanncs.unm.edu> wrote:
> On Aug 11, 2006, at 1:04 PM, Martin DeMello wrote:
>
> > let dawg =
> >   let fd = Unix.openfile "sowpods.dwg"
[ Unix.O_RDONLY ] 0 in
> >   Array1.map_file fd int32 c_layout false -1;;
> >
> > $ ocaml unix.cma bigarray.cma dawgutils.ml
> > File "dawgutils.ml", line 6,
characters 2-41:
> > This expression has type
> >   int -> (int32, Bigarray.int32_elt,
Bigarray.c_layout)
> > Bigarray.Array1.t
> > but is here used with type int
>
> It looks like the compiler might be parsing that as:
> (Array1.map_file fd int32 c_layout false) - 1;;
>
> Changing -1 to ~-1 using the explicit unary negative
works fine.

Ohhh!! I spent over an hour trying to figure out the error
message 
Thanks to both of you!

martin


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