functional programming - How can I convert my data type? -

i define data type multi list: datatype intnest= int of int | list of intnest list; i'm trying write function can convert type main type.

for example: [int 1, int 2, list[int 6, int 8]] => [1,2, [6,8]] how can this? in advance help

with reference your previous question, can't!

as tried explain: not possible have such value in sml!

just try out in interpreter

- val _ = [1,2, [6,8]]; stdin:28.9-28.21 error: operator , operand don't agree [literal]   operator domain: int * int list   operand:         int * int list list   in expression:     2 :: (6 :: 8 :: nil) :: nil 

if construct list basic constructs instead of syntactic sugar, list [1,2,3] becomes 1 :: 2 :: 3 :: nil

now, if @ types of 2 "building blocks" cons , nil

- op::; val = fn : 'a * 'a list -> 'a list - nil; val = [] : 'a list 

then see infix operator cons, takes argument of type 'a on left hand side , list of 'a on right hand side.
can see if build list of ints, must give int on left hand side , list of ints on right hand side (as example above). should clear can't this:

[1, 2] :: 3 :: nil 

which equivalent (1 :: 2 :: nil) :: 3 :: nil