Matching Structured Data

Pattern Matching is much more than just a classic C-style switch statement. In particular, it can be used to match arbitrarily structured data.

Fig 1:

var employee = {name = "Bob", title = "Intern"};

var permission: boolean;
match (employee) {
  case {name = "Sarah", title = "Manager"} -> permission = true;
  case {name = "Joe",   title = "Manager"} -> permission = true;
  case _                                   -> permission = false;
}

print("Permission granted for {employee.name}?: {permission}");

Output:

[0.002s][warning][perf,memops] Cannot use file /tmp/hsperfdata_runner/6 because it is locked by another process (errno = 11)
Permission granted for Bob?: false

Matching Arbitrarily Nested Structured Types

Claro supports pattern matching over arbitrary (i.e. tuple<...> and struct{...}) structured types as their structures are fully known at compile time.

Fig 2:

var player = {name = "Jason", currLoc = (1, 2)};

match (player) {
  case {name = "Sarah", currLoc = (3, 4)} -> print("Sarah wins!");
  case {name = "Jason", currLoc = (1, 2)} -> print("Jason wins!");
  case _                                  -> print("Keep playing...");
}

Output:

Jason wins!