[Caml-list] stack

[Caml-list] stack

[maulin shah]

hi all,
I am a student and learning ocaml. need help for one
problem of Unbound value stack
here is my code.

type ins =PUSH of float| IADD|ISUB;;
type stack = ins list;;
type opn = Add|Sub;;
type exp = Num of float | Opn of exp* opn *exp;;

let rec compile exp=
match exp with 
Num x-> (PUSH x)::stack
|Opn e1,Add,e2 -> compile e2,
                  compile e1,
                  (IADD)::stack;;

gives error : unbound value stack????
 could any one clrify this???

thanks
maulin




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Re: [Caml-list] stack

[Gauthier Nadji]

you define stack as a type and use it in "compile" as a variable.
in the function "compile", the variable "stack" was not declared.
you probably meant this:
#let rec compile e =
 match e with
  Num  x -> [PUSH x]
  |Opn  (e1, o, e2) -> (compile e1) @ (compile e2) 
                    @ [match o with Add -> IADD | Sub -> ISUB];;
-: val compile : exp -> ins list = <fun>
# compile (Opn (Num 5., Add, Num 2.));;
- : ins list = [PUSH 5.000000; PUSH 2.000000; IADD]

the problem is that this function is O(n^3).
this could be done in O(n), which is left as an exercise to 
the student :)

hope this helps despite my obvious lack of pedagogy


On Tue, 13 Feb 2001, maulin shah wrote:

> hi all,
> I am a student and learning ocaml. need help for one
> problem of Unbound value stack
> here is my code.
> 
> type ins =PUSH of float| IADD|ISUB;;
> type stack = ins list;;
> type opn = Add|Sub;;
> type exp = Num of float | Opn of exp* opn *exp;;
> 
> let rec compile exp=
> match exp with 
> Num x-> (PUSH x)::stack
> |Opn e1,Add,e2 -> compile e2,
>                   compile e1,
>                   (IADD)::stack;;
> 
> gives error : unbound value stack????
>  could any one clrify this???
> 
> thanks
> maulin
> 
> 
> 
> 
> __________________________________________________
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Re: [Caml-list] stack

[Ohad Rodeh]

Maulin,
  You have not defined the "stack" variable in your
code, therefore the error message. 

  May I add that I vote Piere should continue with
his thankless job of moderating this list, 

  Just my two cents, 

	Ohad.

----------------------------------------------------------
orodeh@cs.huji.ac.il
www.cs.huji.ac.il/~orodeh



On Tue, 13 Feb 2001, maulin shah wrote:

> hi all,
> I am a student and learning ocaml. need help for one
> problem of Unbound value stack
> here is my code.
> 
> type ins =PUSH of float| IADD|ISUB;;
> type stack = ins list;;
> type opn = Add|Sub;;
> type exp = Num of float | Opn of exp* opn *exp;;
> 
> let rec compile exp=
> match exp with
> Num x-> (PUSH x)::stack
> |Opn e1,Add,e2 -> compile e2,
>                 compile e1,
>                 (IADD)::stack;;
> 
> gives error : unbound value stack????
>  could any one clrify this???
> 
> thanks
> maulin
> 


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Re: [Caml-list] stack

[wester]

> hi all,
> I am a student and learning ocaml. need help for one
> problem of Unbound value stack
> here is my code.
> 
> type ins =PUSH of float| IADD|ISUB;;
> type stack = ins list;;
> type opn = Add|Sub;;
> type exp = Num of float | Opn of exp* opn *exp;;
> 
> let rec compile exp=
> match exp with 
> Num x-> (PUSH x)::stack
> |Opn e1,Add,e2 -> compile e2,
>                   compile e1,
>                   (IADD)::stack;;
> 
> gives error : unbound value stack????
>  could any one clrify this???
> 

I'm an OCaml beginner too but I hope this is what you wanted.
(Any other solutions?) 

type ins = PUSH of float | IADD | ISUB;;
type stack = ins list;;
type opn = Add|Sub;;
type exp = Num of float | Opn of exp * opn * exp;;

let rec compile exp =
  match exp with 
	  Num x            -> (PUSH x)::[]
	| Opn (e1,Add,e2)  -> List.append (List.append (compile e1) (compile e2)) (IADD::[]);
	| Opn (e1,Sub,e2)  -> List.append (List.append (compile e1) (compile e2)) (ISUB::[]);;

let m = Opn (Opn (Num 2.0, Sub, Num 3.0), Add, Num 2.0);;
let stackn = compile m;;

Rolf Wester


-------------------------------------
Rolf Wester
wester@ilt.fhg.de
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