On Wed, Aug 01, 2007 at 09:42:54AM +0200, Georg Martius wrote:
Hi,
I am sorry for using the wrong terminology here. Let me ask again: Does it sound reasonable to extend the compiler with a pragma that specifies that a certain function should be compiled to a loop? And if the compiler can not do it, it helps with some error message.
Unfortunately, that's still almost useless in the presence of laziness. Take the following (contrived) example: fib :: Int -> (Int,Int) -> (Int,Int) fib 0 p = p fib k p = fib (k-1) (snd p, fst p + snd p) That compiles to a perfectly reasonable loop: (minor code rearrangement and bounds-checks deleted for clarity) X_zdszdwfib_info: Hp = Hp + 16; _sjD = I32[Sp + 8]; if (_sjD == 0) goto clk; _sjF = _sjD - 1; I32[Hp - 12] = sjC_info; I32[Hp - 4] = I32[Sp + 4]; I32[Hp] = I32[Sp]; I32[Sp + 8] = _sjF; I32[Sp + 4] = I32[Sp]; I32[Sp] = Hp - 12; jump X_zdszdwfib_info (); clk: I32[Hp - 12] = base_DataziTuple_Z2T_con_info; I32[Hp - 8] = I32[Sp + 4]; I32[Hp - 4] = I32[Sp]; R1 = Hp - 12; Sp = Sp + 12; Hp = Hp - 4; jump I32[Sp] (); Yet still: Prelude X> fib 10000000 (1,1) (*** Exception: stack overflow Since while *your function* may be a loop, the thunks it builds are evaluated in a way that isn't. Stefan