So I've got this list of lists of strings:
[["#@","**","#@"],["##","*%","##"]]
What I want to do is transform each inner list into a single string like this:
["#@**#@","##*%##"]
Resulting in a list of strings.
I've tried various combinations of map, foldr, and anonymous functions, but I can't for the life of me figure out how to achieve my desired result.
There is a function concat : string list -> string in the String structure in the Basis Library, which happens to be at the top level. Therefore, you can define your function:
val concatEach = map concat
It is going to have type string list list -> string list, which I guess is what you are looking for.
If you want to define your own concat function, you can do it this way:
val myConcat = foldr (op ^) ""
Or, without using the op keyword:
val myConcat' = foldr (fn (x, y) => x ^ y) ""
- val myConcat = foldr (op ^) ""; val myConcat = fn : string list -> string - - myConcat([["#@","**","#@"],["##","*%","##"]]); stdIn:1816.1-1816.46 Error: operator and operand don't agree [tycon mismatch] operator domain: string list operand: string list list in expression: myConcat (("#@" :: "**" :: <exp> :: <exp>) :: ("##" :: <exp> :: <exp>) :: nil)
myConcat was just a replacement for the concat function in the library. Have you tried the concatEach function I defined in my answer?concatEach and it did work (I was under the impression that they worked the same way. My mistake. Thank you for your help!