How do you manipulate a list of tuples in SML?

Question

I'm new to SML, and I was wondering how to get an element in a list of tuples. For example, in the list [("abc", 4), ("def", 6)], how could you extract "abc"? I've tried

x::xs => #1(x)

but I keep getting "unresolved flex record". Any suggestions?

Answer 1

You can just extract it using pattern matching.

let
  val lst = [("abc", 4), ("def", 6)]
in
  case lst of (str,_)::xs => str
              | [] => "The list is empty"
end

Will return "abc".

Answer 2

What you posted works too, in a case expression. I don't know what you were trying to do.

let
  val lst = [("abc", 4), ("def", 6)]
in
  case lst of x::xs => #1 x
              | [] => "The list is empty"
end