CODEWITHSUNDEEP
ocaml
Ojmeny
Ojmeny

Reputation: 1426

Error: Unbound value take

I'm learning ocaml and I'm trying to write easy function which prints out firsts given as argument int's.

What I have wrote:

let rec take(number, lista)=
    let rec take_acc(number, lista, acc)=
        match number with
          | 0 -> []
          | number < 0 -> []
          | number > lista.length -> lista
          | number < lista.length -> take_acc(number-1, lista.tl, [email protected]);;
   take_acc(number, lista, [])

let listas = 1 :: 2 :: 3 :: 4 :: 5 :: 6 :: [];;
take(2,listas);;

The point is, that given code above gives me error:

Error: Unbound value take

What I'm doing wrong?

The point is that this code works: 

let xxl = 11 :: 33 :: 54 :: 74 :: [];; 
let rec take2 (ile,xxx) = 
if ile=0 || ile<0 then []
else 
if ile>(List.length xxl) then take2(ile-1,xxx)
else 
List.hd xxx :: take2(ile-1,List.tl xxx);;

Where is difference beetwen these two programs?

EDIT: Due to Jeffrey Scofield's suggestion I have written something like this:

let rec take2(ilosc, lista) =
   let rec take_acc(ilosc, lista, acc) =
       if ilosc = 0 || ilosc < 0 then []
       else
         if ilosc > List.length lista
            then lista
         else
            take_acc(ilosc-1, lista.tl, [email protected]);;

let listas = 1 :: 2 :: 3 :: 4 :: 5 :: 6 :: [];;
take2(2,listas);;

Still the same.

Upvotes: 0

Views: 2067

Answers (1)

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66818

Your code is not syntactically well formed. So it couldn't ever reach the point of saying that take isn't defined.

The first thing to fix is your use of patterns. The construct number < 0 isn't a pattern, it's a boolean expression. You can have a boolean as part of a pattern using when:

| _ when number < 0

However, this isn't particulary good style for what you want to test. It might be better just to use if for your tests.

The next thing to fix might be your use of lista.length. The way to get the length of a list in OCaml is List.length lista.

Upvotes: 2

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