On Wed, Jul 24, 2013 at 1:11 AM, Andreas Abel
On 23.07.13 4:34 AM, Richard A. O'Keefe wrote:
On 22/07/2013, at 8:14 PM, Andreas Abel wrote:
Just today, my student asked me why the following program does nothing:
Did you ask your student why their code should not be torn into pieces, burned to ashes, and incorporated into a pot for radioactive waste?
All those occurrences of unsafePerformIO!
No, here they are intended, to simulate something like uniqueness types in Clean, which incidentially has been mentioned on this thread before.
The loop has nothing to do with unsafePerformIO, but stems from Haskell's idiosyncratic recursive let, which is a trap for all that come from another functional language.
Have your students turn on -fwarn-name-shadowing -Werror: [1 of 1] Compiling Main ( foo.hs, interpreted ) foo.hs:53:16: Warning: This binding for `arr' shadows the existing binding bound at foo.hs:50:28 foo.hs:62:18: Warning: This binding for `arr' shadows the existing binding bound at foo.hs:56:24