On Tue, Mar 12, 2019 at 12:23 PM Hongwei Xi <[email protected]> wrote:
> Here is a quick fix:
> extern
> praxi
> clear{a:t0ype}(x: INV(a)): void
>
> fun open_close(): void =
> let
> val fptr = fopen("hello.dats", file_mode_r)
> val p = ptrcast(fptr)
> in
> if p = 0
> then
> let
> prval () = FILEptr_free_null(fptr)
> in
> end
> else
> let
> val (pf|rc) = fclose(fptr)
> val () = assertloc(rc = 0) // fclose is expected to succeed
> prval None_v() = pf
> prval () = clear(fptr)
> in
> end
> end
>
> ######
>
> The above shows a C-style of dealing with IO in ATS. What I like to
> recommend
> is to deal with IO via the use of linear streams:
>
> https://github.com/ats-lang/ATS-CodeBook/tree/master/RECIPE/ReadFromSTDIN
>
I'm trying to implement tail in ATS as a practice. It seems the streams
interface may not be a good fit in this case. Is there a better way to do
it than the C-style way? (read the last N bytes into a buffer, count the
number of new lines from the end)
>
>
> On Tue, Mar 12, 2019 at 2:17 PM Shimin Guo <[email protected]> wrote:
>
>> I wrote the following code
>>
>> #include "share/atspre_define.hats"
>> #include "share/atspre_staload.hats"
>>
>> staload "libats/libc/SATS/stdio.sats"
>>
>> fun open_close(): void =
>> let
>> val fptr = fopen("hello.dats", file_mode_r)
>> val p = ptrcast(fptr)
>> in
>> if p = 0
>> then
>> let
>> prval () = FILEptr_free_null(fptr)
>> in
>> end
>> else
>> let
>> val (pf|rc) = fclose(fptr)
>> val () = assertloc(rc = 0) // fclose is expected to succeed
>> prval None_v() = pf
>> in
>> end
>> end
>>
>>
>>
>> and got the following compiler error:
>>
>>
>> /home/sguo/ats/file.dats: 242(line=13, offs=7) -- 307(line=16, offs=10):
>> error(3): the dynamic variable [fptr$4718(-1)] is consumed but it should be
>> retained with the type [S2Eapp(S2Ecst(ptr_addr_type);
>> S2Evar(l$8617$8618(14269)))] instead.
>> patsopt(TRANS3): there are [1] errors in total.
>> exit(ATS): uncaught exception:
>> _2home_2hwxi_2Research_2ATS_2dPostiats_2src_2pats_error_2esats__FatalErrorExn(1025)
>>
>>
>>
>> Why does it say fptr should be retained?
>>
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>> .
>>
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