Additional thunk for function

[Victor Nazarov]

Here is some more details:

% ghc -c -ddump-stg T1.hs

==================== STG syntax: ====================
T1.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(T1.map): []


% ghc -c -ddump-stg T1.hs -O

==================== STG syntax: ====================
T1.map =
    \r [f_sel ds_seg]
	case ds_seg of wild_ser {
	  [] -> [] [];
	  : x_sek xs_seo ->
	      let { sat_seq = \u [] T1.map f_sel xs_seo; } in
	      let { sat_sen = \u [] f_sel x_sek; } in  : [sat_sen sat_seq];
	};
SRT(T1.map): []