Reading Characters

get0(X)
get(X)

put(X)

• get0(X) reads a single character from the input stream and instantiates it to X
• get1(X) reads a non-white space character from the input stream and instantiates it to X (white character has ASCII value less than or equal to 32)

  Q: get(X)
     P
  A: X = 80

• MacProlog also provides getb/1 and getx/2 - used to get a byte or word from the keyboard

  Q: getb(Byte)
  (user then hits the left mouse button)
  A: Byte=-1

• put(X) writes a single character to the output stream with the ASCII code X
• Multiple options of put also available in MacProlog
• No backtracking allowed - only a single character and then the goal fails

copy_sentence(Input,Output) :-
 see(Input),
 tell(Output),
 copy,
 seen,
 told.

copy :-
 get0(Ch),
 put(Ch),
 treat([Ch]).

treat(".").
treat( _) :-
 copy.

• copy_sentence copies from a file Input to a file Output - until terminated by a period
• Instead of procedures seen and told, also possible to close the input/output stream with close(Filename)
• When reading, if end of file reached, in the read(X) goal, X is instantiated to end_of_file, and the next read(X) fails
• get0(X) fails immediately if end of file is reached