Question

For my assignment I have to do two functions with the type:

 wt: trie -> (char list list -> ’a)-> ’a
 aw: trie list -> (char list list -> ’a)-> ’a

but what I have is this and was wondering if it was the same thing:

 wt: 'a trie -> ('a list list -> ’a list list)-> ’a list list 
 aw: 'a trie list -> ('a list list -> ’a list list)-> ’a list list

This is my function:

datatype ’a trie = Node of ’a * (’a trie) list | Empty

fun words_in_trie Empty cont = cont [[]]
    | words_in_trie (Node (c, lis)) cont = all_words lis (fn j => map (fn y => [c]@y) j)

Answer 1

No, those are not the same. For each of them, look at the second parameter, the function. Your assignment says:

char list list -> 'a

Your version says:

'a list list -> ’a list list

Okay, so let’s assume that in your function, 'a is char. That means that we can rewrite it to

char list list -> char list list

Which is different from what the assignment says. Of course, the 'a in the assignment could in theory be a char list list, but when it’s specified as 'a, that probably means that your teachers want it to be generic.