I'm not following the details of this thread, but if you guys can come to a conclusion and write up a design, I'd be happy to discuss it. If you want validation of literal strings, then TH quasiquotes are the way to go: [url| http://this/that |] will let you specify the parser/validator to use ("url" in this case) and allow any error messages to be delivered in a civilised way at compile time. I don't really want to make "http://this/that" have exactly this semantics; apart from anything else, which parser do you mean. This is what TH quasiquotation is *for*. Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell- | users-bounces@haskell.org] On Behalf Of Yitzchak Gale | Sent: 24 April 2012 07:46 | To: J. Garrett Morris | Cc: GHC users | Subject: Re: default instance for IsString | | J. Garrett Morris wrote: | > By this logic, head is "unsound", since head [] throws an error. | > Haskell types are pointed; Haskell computations can diverge. | | Well, there are those who would actually agree with that and banish 'head' | and friends from the language. | But I'll agree with you here. | | [As an aside - I'm finding that liberal use of Edward's non-empty list type, | found in the semigroups package, solves many of those problems for me.] | | But there are two crucial differences. First, head is just a partial | function, not basic language syntax. | Second, the divergence of head is constant and well-known, and not dependent | on the implementation of a type class at particular types by various library | authors. | | > What happens after the computation diverges is irrelevant to type | > soundness. | | Agreed. I'm not talking about type soundness, in the technical sense. I'm | talking about engineering soundness. | | Thanks, | Yitz | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users