GET "libhdr"

LET start() BE $(

    // Attempt to open the named files.
    LET source = findinput("input.txt")
    LET destination = findoutput("output.txt")

    TEST source = 0 THEN
        writes("Unable to open input.txt*N")
    ELSE TEST destination = 0 THEN
        writes("Unable to open output.txt*N")
    ELSE $(

        // The current character, initially unknown.
        LET ch = ?

        // Make the open files the current input and output streams.
        selectinput(source)
        selectoutput(destination)

        // Copy the input to the output character by character until
        // endstreamch is returned to indicate input is exhausted.
        ch := rdch()
        UNTIL ch = endstreamch DO $(
            wrch(ch)
            ch := rdch()
        $)

        // Close the currently selected streams.
        endread()
        endwrite()
    $)
$)