-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 19-01-12 14:13, Matthew Flatt wrote: > The `frtime' language exports an `=' that isn't the same as `=' in > `racket', so that's why the pattern doesn't match. (This seems like > a further weakness of the `frtime' docs to specify the exports > precisely.) > > You could avoid bound names like `=' as literals in the macro. > Normally, it works best for a form-exporting macro to also export > bindings for any literals in the form. Otherwise, this kind of > confusion is common.
I think I will change the `=' to `!' for now. What kind of binding should I use for `?' and `!'? There is no sensible meaning to be bound to them... What do you use to bind `else'? > Alternatively, you may want to match literals in your macro > symbolically instead of by binding. You can't do that easily with > `syntax-rules', but you can use `syntax-case*' and supply `(lambda > (a b) (eq? (syntax-e a) (syntax-e b)))' as the literal-comparison > function. > > If it were me and I decided to go in the direction of symbol > equality, I'd use keywords instead --- `#:?' and `#:=' instead of > `?' and `=' --- which makes clear that there's no question of > binding. When cond starts using #:else I might consider this more seriously. The docs seem now less than clear to me about the difference between a keyword and a symbol. The reference claims that "A keyword is like an interned symbol, but ... and a keyword cannot be used as an identifier" implying that symbols can be used as identifiers. I have in my head from unknown source (maybe from other schemes) that a keyword is a value which evaluates to itself, like a constant, whereas symbols are produced by quoting identifiers. The difference manifesting when multiple-evaluation comes into play: what is the value of the value of ... Marijn -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk8ZYe8ACgkQp/VmCx0OL2zGjwCfT3PTlGrlicqHKo4ww0TcCicq Ku8An3dTq+bnD+YYM5hCh61n6zadzo3h =ScwW -----END PGP SIGNATURE----- _________________________ Racket Developers list: http://lists.racket-lang.org/dev
