Additional thunk for function

[Victor Nazarov]

What is the purpose for GHC to allocate a thunk for some functions?
Why Test.map is not a function, but updatable thunk, which should
become equal to the function just after the first call? Here is the
details:

> % ghc -c test.hs -ddump-stg
>
> ==================== STG syntax: ====================
> Test.map =
>     \u []
> 	let {
> 	  map1_sdR =
> 	      \r [f_sdN ds_sdI]
> 		  case ds_sdI of wild_sdU {
> 		    [] -> [] [];
> 		    : x_sdM xs_sdQ ->
> 			let { sat_sdT = \u [] map1_sdR f_sdN xs_sdQ; } in
> 			let { sat_sdP = \u [] f_sdN x_sdM; } in  : [sat_sdP sat_sdT];
> 		  };
> 	} in  map1_sdR;
> SRT(Test.map): []
>
>
> % cat test.hs
> module Test where
>
> map f [] = []
> map f (x:xs) = f x : Test.map f xs

--
Thanks in advance
Victor