[SLOF] [PATCH v5 1/2] Fix output word

[Thomas Huth]

On 27.03.2018 13:23, Laurent Vivier wrote:
> On 26/03/2018 13:11, Thomas Huth wrote:
>> On 26.03.2018 13:06, Thomas Huth wrote:
>>> On 23.03.2018 12:42, Laurent Vivier wrote:
>>>> We can select the console output, but it does not really work
>>>>
>>>> Implement term-io-emit, as we have term-io-key to really
>>>> send characters to the output selected by stdout.
>>>>
>>>> Signed-off-by: Laurent Vivier <lvivier at redhat.com>
>>>> ---
>>>>  slof/fs/term-io.fs | 33 ++++++++++++++++++++++++++++-----
>>>>  1 file changed, 28 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/slof/fs/term-io.fs b/slof/fs/term-io.fs
>>>> index 52ce12a..97d02a4 100644
>>>> --- a/slof/fs/term-io.fs
>>>> +++ b/slof/fs/term-io.fs
>>>> @@ -10,6 +10,17 @@
>>>>  \ *     IBM Corporation - initial implementation
>>>>  \ ****************************************************************************/
>>>>  
>>>> +0 VALUE write-xt
>>>> +
>>>> +VARIABLE stdout
>>>> +
>>>> +: set-stdout ( ihandle -- )
>>>> +   \ Close old stdout:
>>>> +   stdout @ ?dup IF close-dev THEN
>>>> +   \ Now set the new stdout:
>>>> +   dup stdout !
>>>> +   encode-int s" stdout" set-chosen
>>>> +;
>>>>  
>>>>  : input  ( dev-str dev-len -- )
>>>>     open-dev ?dup IF
>>>> @@ -24,12 +35,15 @@
>>>>  
>>>>  : output  ( dev-str dev-len -- )
>>>>     open-dev ?dup IF
>>>> -      \ Close old stdout:
>>>> -      s" stdout" get-chosen IF
>>>> -         decode-int nip nip ?dup IF close-dev THEN
>>>> +      \ find new ihandle and xt handle
>>>> +      dup s" write" rot ihandle>phandle find-method
>>>> +      0= IF
>>>> +         drop
>>>> +         cr ." Cannot find the write method for the given output console " cr
>>>> +         EXIT
>>>>        THEN
>>>> -      \ Now set the new stdout:
>>>> -      encode-int s" stdout" set-chosen
>>>> +      to write-xt
>>>> +      set-stdout
>>>>     THEN
>>>>  ;
>>>>  
>>>> @@ -40,6 +54,15 @@
>>>>  
>>>>  1 BUFFER: (term-io-char-buf)
>>>>  
>>>> +: term-io-emit ( char -- )
>>>> +    write-xt 0= IF drop EXIT THEN
>>>
>>> Patch looks basically fine to me, but this part is a little bit ugly: As
>>> long as write-xt is 0, there won't be a way to print out any console
>>> output. So between the point in time where term-io.fs is included (i.e.
>>> tree.fs in OF.fs) and the point in time where "output" is called, there
>>> won't be any console output anymore.
>>> To fix this, use the trick that is already used in term-io-key:
>>>
>>>   write-xt 0= IF [ ' emit behavior compile, ] THEN
>>
>> And of course there should also be an "EXIT" before the "THEN" in this
>> case :-)
> 
> I did this in v2 of the patch, but Segher said:
> 
>> That is very problematic.  If the xt of term-io-emit already is the
>> behaviour of emit, this will loop.

I'm afraid to object Segher, but as far as I can see, this can not
happen. The "[ ' emit behavior compile, ]" happens *while* the Forth
word is compiled, and the first "' term-io-emit to emit" happens *after*
the Forth word is compiled. So how should the term-io-emit XT end up in
"emit" before the term-io-emit Forth word is compiled?

Since we're also using that logic in term-io-key and never encountered a
loop here so far, I think it's safe to go ahead and use this for
term-io-emit, too.

 Thomas