Hi there, I am trying to write my first serious Haskell program, but have problems understanding 'strange' performance results. It seems to be a ghc specific question, so I am asking here. In a happy parser I have this code 1): %monad { Parsed } { thenP } { returnP } type Parsed = State Env.Env returnP :: a -> Parsed a returnP a = return a thenP :: Parsed a -> (a -> Parsed b) -> Parsed b thenP x k = x >>= k An alternative was this 2) (yes, redundant in happy): returnP :: a -> Parsed a returnP = return thenP :: Parsed a -> (a -> Parsed b) -> Parsed b thenP = (>>=) And strangely enough on my machine 1) is faster by a few percent than 2) using ghc 6.8.2 with -O2. A few percent might seem unimportant, but I am currently developing my Haskell style. And I want to write efficient code by default, if that doesn't lead to obfuscation. Now, first I dislike using option 1) because it seems pointlessly verbose. Second, I have no clue why option 2) should be faster. Using ghc -O2 -C I get two code blocks with 1) (appended at the end of this mail), whereas I get nothing with 2. Unfortunately, that doesn't help me as I have no clue what it means. There are also various strictness annotations throughout the code to make parsing less memory hungry (and getting an intuition about what is appropriate here drives me crazy). Random guess: perhaps somehow strictness analysis of ghc benefits from the code in 1)? Or does ghc create specialized versions of return and >>= for State instantiated to Parsed, i.e. State Env.Env? Anyhow, I am puzzled and grateful for any explanations and recommendations about what is going on and when to avoid style 2). Thanks, Alexander C-- code blocks: ------------------------------------------------------- EI_(DarwinziTptpziParser_a106_info); StgWord DarwinziTptpziParser_a106_closure[] = { (W_)&DarwinziTptpziParser_a106_info }; static StgWord s8Ey_info[] = { 0x42U, 0x22U }; IF_(s8Ey_ret) { W_ _c8EL; FB_ Sp[2] = *((P_)(R1.w+7)); _c8EL = *((P_)(R1.w+3)); R1.w = Sp[1]; Sp[1] = _c8EL; Sp=Sp+1; JMP_((W_)&stg_ap_pp_fast); FE_ } StgWord DarwinziTptpziParser_a106_info[] = { 0x30014U, 0x0, 0xfU }; EI_(DarwinziTptpziParser_a106_closure); II_(s8Ey_info); FN_(DarwinziTptpziParser_a106_entry) { FB_ if ((W_)(((W_)Sp - 0x4U) < (W_)SpLim)) goto _c8EO; R1.w = *Sp; Sp[-1] = Sp[2]; *Sp = (W_)&s8Ey_info; Sp=Sp-1; JMP_((W_)&stg_ap_p_fast); _c8EO: R1.w = (W_)&DarwinziTptpziParser_a106_closure; JMP_(stg_gc_fun); FE_ } ------------------------------------------------------- ------------------------------------------------------- II_(r6AT_info); static StgWord r6AT_closure[] = { (W_)&r6AT_info, 0x0, 0x0, 0x0 }; static char c97W_str[] = "Internal Happy error\012"; static StgWord r6AT_info[] = { 0x0, 0x16U }; EI_(base_GHCziBase_unpackCStringzh_info); IF_(r6AT_entry) { FB_ if ((W_)(((W_)Sp - 0xcU) < (W_)SpLim)) goto _c97Z; Hp=Hp+2; if ((W_)((W_)Hp > (W_)HpLim)) goto _c97Z; Hp[-1] = (W_)&stg_CAF_BLACKHOLE_info; newCAF((void *)R1.w); R1.p[1] = (W_)Hp-4; *R1.p = (W_)&stg_IND_STATIC_info; Sp[-2] = (W_)&stg_upd_frame_info; Sp[-1] = (W_)Hp-4; Sp[-3] = (W_)&c97W_str; Sp=Sp-3; JMP_((W_)&base_GHCziBase_unpackCStringzh_info); _c97Z: HpAlloc = 0x8U; JMP_(stg_gc_enter_1); FE_ } EI_(base_GHCziErr_error_closure); II_(r6AT_closure); StgWord DarwinziTptpziParser_notHappyAtAll_srt[] = { (W_)&base_GHCziErr_error_closure, (W_)&r6AT_closure }; EI_(DarwinziTptpziParser_notHappyAtAll_info); StgWord DarwinziTptpziParser_notHappyAtAll_closure[] = { (W_)&DarwinziTptpziParser_notHappyAtAll_info, 0x0, 0x0, 0x0 }; StgWord DarwinziTptpziParser_notHappyAtAll_info[] = { ((W_)&DarwinziTptpziParser_notHappyAtAll_srt+0), 0x0, 0x30016U }; EI_(base_GHCziErr_error_closure); II_(r6AT_closure); FN_(DarwinziTptpziParser_notHappyAtAll_entry) { FB_ if ((W_)(((W_)Sp - 0xcU) < (W_)SpLim)) goto _c989; Hp=Hp+2; if ((W_)((W_)Hp > (W_)HpLim)) goto _c989; Hp[-1] = (W_)&stg_CAF_BLACKHOLE_info; newCAF((void *)R1.w); R1.p[1] = (W_)Hp-4; *R1.p = (W_)&stg_IND_STATIC_info; Sp[-2] = (W_)&stg_upd_frame_info; Sp[-1] = (W_)Hp-4; R1.w = (W_)&base_GHCziErr_error_closure; Sp[-3] = (W_)&r6AT_closure; Sp=Sp-3; JMP_((W_)&stg_ap_p_fast); _c989: HpAlloc = 0x8U; JMP_(stg_gc_enter_1); FE_ } -------------------------------------------------------