Defer statement

Instead of a try finally statement a defer statement can be used.

Any statements following the defer in the current block will be considered to be in an implicit try block:

proc main =
  var f = open("numbers.txt")
  defer: close(f)
  f.write "abc"
  f.write "def"

Is rewritten to:

proc main =
  var f = open("numbers.txt")
  try:
    f.write "abc"
    f.write "def"
  finally:
    close(f)

Top level defer statements are not supported since it’s unclear what such a statement should refer to.