[Caml-list] Let-in vs beta-redex

[Caml-list] Let-in vs beta-redex

[Lukasz Stafiniak]

Hi,

Is let-in more efficient than beta-redex or are they computationally
equivalent? Is let-in a syntax-sugar of beta-redex?

E.g.

let x = sin 2. in x *. x *. x;;

(fun x -> x *. x *. x) (sin 2.);;

Thank You in advance,
Kindest Regards,
Lukasz



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RE: [Caml-list] Let-in vs beta-redex

[John Gerard Malecki]

Lukasz Stafiniak wrote (2003-09-01T18:15:54+0200):
 > Hi,
 > 
 > Is let-in more efficient than beta-redex or are they computationally
 > equivalent? Is let-in a syntax-sugar of beta-redex?

They may be conceptually different but they compile to pretty much teh
same thing.  A nice trick to learn about the code that ocamlc
generates is to use 'ocaml -dinstr'.  For example,


:; ocaml -dinstr
        Objective Caml version 3.07+beta 2

# let x = sin 2. in x *. x *. x;;
        const 2.
        ccall sin_float, 1
        push
        acc 0
        push
        acc 1
        push
        acc 2
        ccall mul_float, 2
        ccall mul_float, 2
        return 2

- : float = 0.751826944668992803
# (fun x -> x *. x *. x) (sin 2.);;
        const 2.
        ccall sin_float, 1
        push
        closure L1, 0
        appterm 1, 2
L1:     acc 0
        push
        acc 1
        push
        acc 2
        ccall mul_float, 2
        ccall mul_float, 2
        return 1

- : float = 0.751826944668992803
# 

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Re: [Caml-list] Let-in vs beta-redex

[Michal Moskal]

On Mon, Sep 01, 2003 at 06:15:54PM +0200, Lukasz Stafiniak wrote:
> Hi,
> 
> Is let-in more efficient than beta-redex or are they computationally
> equivalent? Is let-in a syntax-sugar of beta-redex?
> 
> E.g.
> 
> let x = sin 2. in x *. x *. x;;
> 
> (fun x -> x *. x *. x) (sin 2.);;

let in is *not* equivalent to beta-redex because of typing. Type
variables are not generalized in beta-redex, for example consider:

let id x = x in
(id 1, id true)

vs.

(fun id -> (id 1, id true)) (fun x -> x)

-- 
: Michal Moskal :: http://www.kernel.pl/~malekith : GCS {C,UL}++++$ a? !tv
: PLD Linux ::::::::: Wroclaw University, CS Dept : {E-,w}-- {b++,e}>+++ h

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