Question

I try to find a library function in ML that equal to (cdr string) in Scheme (meaning (cdr abcd) = bcd).

Answer 1

(Asuming SML)

Another way is to convert the string to a list of chars (explode), then you have the option to take the head (hd) or tail (tl), and then finally convert it back to a string (implode):

- (implode o tl o explode) "this is a string";
val it = "his is a string" : string

The string conversion functions can be found in the String module, and the head and tail functions can be found in the List module

Obviously you can also use the substring method here, however in SML you have the extract function that are quite convenient in this case:

- String.extract("This is a string", 1, NONE);
val it = "his is a string" : string

Giving it the NONE argument makes it extract until the end of the string.