Thank you very much. That clears everything right up. -Hillary On Wed, Jun 13, 2012 at 4:11 PM, Stephen Bloch <bl...@adelphi.edu> wrote:
> > 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 > >
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