Custom label level types

[HuseyinSimsek7904]

Custom label level types can be useful to make sure that the xyz.init and xyz.end macros like sb.init and sb.end match. For example:

// '#block' must be ended with a '#endblock', otherwise the compiler will complain.
// This makes sure that 'sb.init' must be ended with a 'sb.end'.

// Create a string builder.
macro sb.init
  #block !!sb.block
  memory _sb.array_ sizeof(ptr) in
  memory _sb.ptr_   sizeof(ptr) in
    _sb.array_ _sb.ptr_ string-builder.init
endmacro

// Dump the contents to a stream and deallocate the string builder.
macro sb.end // file-desc: stream-to-dump
    let stream in
      // Dump the generated string.
      _sb.array_ _sb.ptr_ string-builder.to-array stream fputs

      // Deallocate the string builder object.
      _sb.array_ @64 mfree drop
    end
  end end
  #endblock !!sb.block
endmacro

// This is fine.
sb.init
  "hello, world!\n" sb.add-str
STDOUT sb.end

// This is not fine, `sb.end` ends `if`.
sb.init
  x 2 > if
  STDOUT sb.end
end