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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: wait does not perform as expected
Date: Thu, 23 Feb 2023 19:49:04 +0200
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On 2023-02-23 19:35, Niklas Holsti wrote:
> On 2023-02-23 16:26, AdaMagica wrote:
>> Niklas Holsti schrieb am Mittwoch, 22. Februar 2023 um 18:36:06 UTC+1:
>>> On my system, Get_Immediate does /not/ use the inputs collected (but not
>>> "consumed") by Look_Ahead, but instead checks if there are _new_ input
>>> keystrokes. If there are none, Get_Immediate returns "not Available"
>>> (Hit is False) and so the loop continues.
>>
>> Are you sure?
> 
> 
> That is what I observe.
> 
> 
>> With GNAT Community 2021 (20210519-103) targeting x86_64-w64-mingw32,
>>
>>    loop
>>      Look_Ahead    (Char, EoL);  Put ("Look_Ahead:    '" & Char & "', 
>> End_of_Line => " & EoL'Image);  New_Line;
>>      Get_Immediate (Char, Avl);  Put ("Get_Immediate: '" & Char & "', 
>> Available   => " & Avl'Image);  New_Line;
>>    end loop;
>>
>> I get:
>>
>> ab x<RETRUN>
>> Look_Ahead:    'a', End_of_Line => FALSE
>> Get_Immediate: 'a', Available   => TRUE
>> Look_Ahead:    'b', End_of_Line => FALSE
>> Get_Immediate: 'b', Available   => TRUE
>> Look_Ahead:    ' ', End_of_Line => FALSE
>> Get_Immediate: ' ', Available   => TRUE
>> Look_Ahead:    'x', End_of_Line => FALSE
>> Get_Immediate: 'x', Available   => TRUE
>> Look_Ahead:    '0', End_of_Line => TRUE
>> Get_Immediate: '                                          <- This is 
>> the EoL
>> ', Available   => TRUE
>>
> 
> 
> On my system:
> 
> ab x<RETURN>
> Look_Ahead:    'a', End_of_Line => FALSE
> Get_Immediate: '', Available   => FALSE
> Look_Ahead:    'a', End_of_Line => FALSE
> Get_Immediate: '', Available   => FALSE
> Look_Ahead:    'a', End_of_Line => FALSE
> Get_Immediate: '', Available   => FALSE
> 
> and so on for ever, with Look_Ahead never waiting for new input.
> 
> The behaviour on my system is certainly different from yours. I can see 
> that both behaviours could be useful, depending on the program's needs. 
> However, I was certainly surprised to see my system's behaviour, and a 
> priori I expected to get the behaviour you see.
> 
> My system is oldish:
> 
> GNAT Community 2019 (20190517-83)
> macOS 10.14.6 Mojave
> 
> This difference appears when mixing Look_Ahead and Get_Immediate, 


Or (on my system) when mixing ordinary Get and Get_Immediate. If I 
replace the Look_Ahead call with just a test for End_Of_Line and then 
Get (Char), I get a similar effect, showing that on my system 
Get_Immediate ignores any previously buffered, unconsumed input line, 
whether it results from Look_Ahead or from Get:

ab x
Get          :    'a', End_of_Line => FALSE
Get_Immediate: '', Available   => FALSE
Get          :    'b', End_of_Line => FALSE
Get_Immediate: '', Available   => FALSE
Get          :    ' ', End_of_Line => FALSE
Get_Immediate: '', Available   => FALSE
Get          :    'x', End_of_Line => FALSE
Get_Immediate: '', Available   => FALSE
Get          :    '', End_of_Line => TRUE
Get_Immediate: '', Available   => FALSE

and then the Get call waits for new input (a new input line).