Haskell as a first language... I've seen it work, but the learner was a physicist working on his PhD. "Finally a language that makes sense", he said.
For a 13-year-old who has probably not been exposed to much mathematical rigor at school, I would not recommend Haskell, though. Haskell makes it hard to write a program that, as ugly and unmaintainable as it may be, somehow mostly works (e.g. you have to plan ahead which parts of the program may perform I/O).
Therefore, I'd go with an imperative language and reserve Haskell for the day when he asks "is that all there is?".
Those are good points. However, I don't think Haskell is that much harder than something like SQL once you really understand what's going on. Although it's not much more than an informed hypothesis, I do think that a precocious 13 year old could do well with it... but I would definitely teach an imperative language too.
For a 13-year-old who has probably not been exposed to much mathematical rigor at school, I would not recommend Haskell, though. Haskell makes it hard to write a program that, as ugly and unmaintainable as it may be, somehow mostly works (e.g. you have to plan ahead which parts of the program may perform I/O).
Therefore, I'd go with an imperative language and reserve Haskell for the day when he asks "is that all there is?".