On 9/17/12 6:47 PM, Kieron Hardy wrote:
Hi all,Can anyone explain why the first function below selects 'x1-case as expected but the second fails to select 'x2-case? Am I expecting something to happen that shouldn't? Thanks, Kieron. **** #lang racket (case 'a ['a 'x1-case] ['b 'x1-case] [(15 2 3) 'y1-case] [(10 11 12) 'z1-case]) (case 'a [('a 'b) 'x2-case] [(15 2 3) 'y2-case] [(10 11 12) 'z2-case])
Be careful with quote in a case clause -- those clauses are already implicitly quoted. The first is really:
(case 'a [(quote a) 'x1-case] [(quote b) 'x1-case] [(15 2 3) 'y1-case] [(10 11 12) 'z1-case]) So you'll notice the following surprising behavior: (case 'quote ['a 'x1-case] ['b 'x1-case] [(15 2 3) 'y1-case] [(10 11 12) 'z1-case]) You want: (case 'quote [(a) 'x1-case] [(b) 'x1-case] [(15 2 3) 'y1-case] [(10 11 12) 'z1-case]) and: (case 'a [(a b) 'x1-case] [(15 2 3) 'y1-case] [(10 11 12) 'z1-case]) David ____________________ Racket Users list: http://lists.racket-lang.org/users
