On Jun 13, 2012, at 3:16 PM, Hillary Ryan wrote: > Why does this work? > (define canvas (new canvas% [parent window] [paint-callback (lambda (canvas > dc) (draw canvas dc))])) > > But this doesn't > (define canvas (new canvas% [parent window] [paint-callback (draw canvas > dc)])) > > It seems that in both cases the paint-callback is being set to a 2-arity > procedure.
No, "(draw canvas dc)" is the RESULT of a 2-arity procedure. "draw" (no parentheses, no arguments) would be a 2-arity procedure, equivalent to "(lambda (canvas dc) (draw canvas dc))". > However, in the second case the window doesn't update unless draw is called > from REPL. Yes, that's because you're only calling draw once, at the time you define canvas. Stephen Bloch sbl...@adelphi.edu ____________________ Racket Users list: http://lists.racket-lang.org/users
