Empty string pattern syntax error

[Isaac Elliott]

Test program

test.ipso:

main : IO ()
main =
  case "hello" of
    "" -> println "empty"
    _ -> println "not empty"

Actual output

$ ipso test.ipso 
test.ipso:4:6: error: expected one of: string
  |
4 |     "" -> println "empty"
  |      ^

Expected output

$ ipso test.ipso
not empty