4.1 Row polymorphism

Row polymorphism allows you to write a function that can operate on some fields of a record, without knowing the other fields. Unlike subtyping, the other fields are not lost.

  var x = (a=1, b="Hello", c=42.5, d=99);
  match x with
  | (c=cv, a=1 | r) => 
    println$ "c=" + cv.str +  ", a=1," + " r="+ r._strr;
  endmatch;
  
  fun f[T] (x: (a:int, c:double | T)) =>
    match x with
    | (a=av,c=cv | r) =>  (a=(av+1),c=cv*cv | r)
    endmatch
  ;
  
  var r = f x;
  println$ r._strr;

c=42.5, a=1, r=(b='Hello',d=99)
(a=2,b='Hello',c=1806.25,d=99)