Ocaml: error type -

can explain why have error in code ?

it take 2 list a1, a2, a3 ... , b1 b2 b3 ... produce a1, b1, a2, b2, a3, b3 ...

but error appears

error: expression has type int expression expected of type          int list

example of use: append [1; 2; 3] [4; 5; 6];; code:

let rec append b =  if list.length == 0 && list.length b == 0 [] else (list.hd :: list.hd b) :: append (list.tl a) (list.tl b);;

this should work properly, doesn't... how can fix ?? thanks!

this precedence problem. can't write this:

(1 :: 2) :: []

the right hand operand of :: must list.

you have write this:

1 :: (2 :: [])

if remove parentheses around (list.hd :: list.hd b) should past problem.

as side comment, more idiomatic use pattern matching list.length, list.hd, , list.tl.

what code supposed if lists different lengths?

And