A Confession
This program doesn’t work!
tick :: String -> IO Integer
tick f =
do contents <- readFile f
let n = read contents
writeFile f (show (n+1))
return n
The file is only
opened here, it
is read when
contents is needed.
Not needed yet!
n isn’t needed…
Not needed until
after the file is
opened for writing!
Föregående bild
Nästa bild
Tillbaka till första bilden
Visa grafisk version