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I'm writing a prolog program with an input loop. A good deal of the input is pre-scripted in a response file. I execute this as prolog < response.txt. When the response file has finished, I would like the program to continue through keyboard user input. However, when the response file finishes, it does not read/1 from the keyboard, but continues to read in an endless loop end_of_file as its input.

I want the program to revert to user typed input once the pipe has reached the end of the file. How do I do this?

Thanks in advance.

lildigiman
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  • You may have to show the bit of code that you are using to detect that the file has gotten to the end. – Vincent Ramdhanie Dec 09 '12 at 14:37
  • It is not clear why you want this - do you want to emulate user input? `cat response.txt - prolog` might be good enough. Otherwise indicate the file explicitly with a command line argument. – false Dec 09 '12 at 16:15
  • My program has a cli where, yes, I want to emulate user input, which I've been doing with prolog < response.txt. @VincentRamdhanie, my code shouldn't have anything to do with this; when I reach the end of the response file it should just stop and wait for a user to give user input, instead it just keeps going saying that "end_of_file" is what the user is typing in. – lildigiman Dec 09 '12 at 19:24
  • @false, I tried `cat response.txt - prolog` but that just displays the response.txt to the screen and prolog doesn't do anything with it. – lildigiman Dec 09 '12 at 19:29
  • I meant that there is a bar like | ('|') between `-` and `prolog` – false Dec 09 '12 at 19:32
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    `cat response.txt - | prolog` – false Dec 09 '12 at 19:33
  • Ahhh, a shame I didn't even think to catch that... let me see if that works... – lildigiman Dec 09 '12 at 19:34

1 Answers1

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It is possible to interrogate and redirect your input stream.

Not sure which version of Prolog you're using, but SWI-Prolog has plenty of methods for redirecting your input stream.

If the input is from a keyboard, TTY will equal true:

current_input(Stream), stream_property(Stream, tty(TTY)).

If the input is from a file, Filename will each the name of the file input is currently read from:

current_input(Stream), stream_property(Stream, file_name(Filename)).

You can set the Stream to use as an input with the set_input/1 predicate:

{obtain a Stream handle}, set_input(Stream).

I hope you can build upon this, as I haven't yet figured out how you're supposed to ask for the keyboard input Stream.

You might have to determine which OS you're running on and set up different methods for each OS to set your input to the keyboard stream.

Raceimaztion
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