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tyi(+Stream, -Code)

Succeeds if the code of the next character read in raw mode from the input stream Stream is successfully unified with Code.
Stream handle or alias (atom)
Variable or integer.


Takes the next character from the unbuffered input stream Stream and unifies its integer character code (in the range 0 to 255) with Code. The input is in raw mode so that no newline character must be typed, and the character is not echoed on the screen.

Character codes for the non-printable characters (i.e. control characters) are also acceptable.

Note tyi/2 reads from the stream in raw mode. If it is combined with the buffered predicates, it might happen that some characters typed ahead may be lost if the input device is a terminal.

Modes and Determinism


(4) instantiation fault
Stream is not instantiated.
(5) type error
Stream is neither a stream handle nor an atom.
(5) type error
Code is instantiated, but not to an integer.
(190) end of file reached
End of file has been reached.
(192) illegal stream mode
Stream is not an input stream.
(193) illegal stream specification
Stream is an illegal stream specification.
(198) reading past the file end
Trying to read even after the error 190 was raised.


      ?- tyi(input,Code).
      Code = 97         % press 'a'

      ?- tyi(input,97).
                            % press 'a'

      ?- tyi(input,Code).
      Code = 4          % press ^D

      ?- tyi(input, 0'b).
                            % press 'a'

      tyi(Stream,98).             (Error 4).
      tyi(input, '98').           (Error 5).
      tyi(input, 98.0).           (Error 5).
      tyi("string", A).           (Error 5).

      ?- open(file1,update,s), write(s,p),
         seek(s,0), tyi(s,Code),
      tyi(s,Code).              (Error 190).
      tyi(9,A).                  (Error 192).
      tyi(atom,A).               (Error 193).

See Also

tyi / 1, tyo / 1, tyo / 2