Re: is there a switch or cond-statement? + type-problem

[Chris Conway <cconway@cs.nyu.edu>]

circ ular <circularfunc <at> gmail.com> writes:

> 
> how can I do like this or use cond or case?
> def power(nbr, po):
>     if po > 0:
>         return nbr * power(nbr, po-1)
>     if po < 0:
>         return 1 / power(nbr, -1 * po)
>     if po == 0:
>         return 1
> 
> and ofc make it tailrecursive but that I know how.

The closest thing to "cond" or "case" in OCaml is "match", but "if-then-else" is
probably clearer. In any case, here's how you could do it with "match":

let rec powerx(n, pow, acc) =
    match pow with
      | 0.0 -> acc
      | x when x < 0.0 -> 1.0 /. powerx(n, pow *. (-1.0), acc)
      | _ ->  powerx(n, pow -. 1.0, acc *. n);;

The "x" in the second case matches any floating point number, but the "when"
clause restricts it to negatives. The "_" in the last case therefore matches
only positive numbers.

> 
> also, how do I get it to be a float-function?
> 
> let rec powerx(n, pow, acc) =
>     if pow > 0.0
> 	then powerx(n, pow -. 1, acc *. n)
> 	else if pow < 0.0
> 	    then 1.0 /. powerx(n, pow *. (-1), acc)
> 	    else acc ;;
> 
> Characters 70-71:
>   	then powerx(n, pow -. 1, acc *. n)
>                          ^
> This expression has type int but is here used with type float
> #
> 
> but it is used with float evrywhere no?


"1" is a int constant. Use "1." or "1.0" for floats.

Regards,
Chris

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