Here is an example of a function that prints the numbers from
1 to 100. The function prints 20 numbers at a time waiting
for the user to press Cntrl-D after having printed 20 numbers:

Print20AtATime := function( )
    local  i;
    for i  in [ 1 .. 100 ]  do
        Print( i, "\n" );
        if i mod 20 = 0  then
            Print( "Press Cntrl-D" );
            Read( "*stdin*" );
        fi;
    od;
end;

The trick is to use the statement Read("*stdin*") in order to
read from standard input. However, I cannot see how one can erase
the "Press Cntrl-D" since GAP produces a newline after it has read
Cntrl-D.

Werner Nickel
Mathematics Research Section
Australian National University