[Inquiry] Re: Theme One Program -- Commentary

[Jon Awbrey]

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TOP.  Commentary Note 3

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In this first pass over the code I will focus on the more generic
functionalities of the program and tread lightly by the low level
primitives that are peculiar to this particular version of Pascal.
As a general rule I will be transforming most of the basic Pascal
input-output procedures into a roughly equivalent functional form.

Video.

procedure video (what: mode);
 begin
  case what of
   null: textcolor (0);
   moot: textcolor (7);
   firm: textcolor (14)
  end
end;

This procedure sets the screen display to one of three colors:
null = black on black, moot = dim blue, firm = bright yellow.

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Stop.

procedure stop;
var mark: char;
begin
 write ('< press any key > ');  repeat until keypressed;
 mark := readkey
end;

This procedure writes a prompt and waits for a keypress.

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Just.

function just (this: idea): idea;
begin
 just := nil
end;

This is a function from ideas to ideas
that constantly outputs the 'nil' idea.

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Clear.

function clear (this: idea): idea;
begin
 clear := this;  clrscr
end;

This is a function from ideas to ideas,
that acts as the identity on the input,
with a side-effect to clear the screen.

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Clean.

function clean (this: idea): idea;
begin
 clean := just (clear (this))
end;

This is a function from ideas to ideas,
that constantly outputs the 'nil' idea,
with a side-effect to clear the screen.

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