Hi, Am Freitag, den 06.02.2015, 15:54 -0500 schrieb Gershom B:
I guess the remaining question is then where to add them. I suppose we could stick them with special semantics on Num and IsString or the like and do it by magic?
speaking about magic. This reminds me of https://ghc.haskell.org/trac/ghc/ticket/9180 which would add a function staticError that, if present in the core after RULES had processed, would emit a library author defined error at compile time. So if you can implement your validation in terms of RULES, then you can have RULES insert staticError expressions in the code if validation fails. In order to be useful for your purpose, you probably need the RULES mechanism beefed up a bit, e.g. to allow implications, “magic” predicates like "isLiteral" and some level of evaluation that might be beyond what’s possible now, and eventually lead to something like the static functions discussed in this thread, though. Greetings, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org