[Template-haskell] RE: Documentation Template Haskell

[Simon Peyton-Jones]

| It would be good if it contains some explanations. Recently
| I have found the following example on the mailing list but I can
| only guess what, e.g., "tupP" means.
| 
| sel' :: Int -> Int -> ExpQ
| sel' i n = lamE [pat] rhs
|     where pat = tupP (map varP as)
|           rhs = varE (as !! (i - 1))
|           as = map mkName [ ("a__" ++ show j) | j <- [1..n] ]

tupP has type [Q Pat] -> Q Pat
http://www.haskell.org/ghc/docs/latest/html/libraries/template-haskell/L
anguage-Haskell-TH-Lib.html#v%3AtupP

It's a "smart constructor" for patterns, just like the other "smart
constructors" described in the original TH paper (section 6.3)
http://research.microsoft.com/%7Esimonpj/Papers/meta-haskell/index.htm
[In the paper, the type Expr is now ExpQ, or equivalently Q Exp.]

Does that help?

Simon