0.16.0 Released

Friday, July 28, 2017 | Posted in Release

Pony 0.16.0 is an awesome step forward but its also going to be a painful step forward. 0.16.0 features the implementation of the “Explicit partial calls” RFC. It is going to break almost every single Pony codebase out there. There are no high priority bug fixes in this release so, you can take your time upgrading.

Explicit partial calls

In Pony 0.16.0, we’ve introduced a breaking syntax change that affects all calls to partial functions (functions that can raise an error).

All partial function calls are now required to be followed by a question mark.

For example, iterator.next() is now iterator.next()?, providing a visual indication at the call site of any places where an error may be raised.

Call sites to partial functions that fail to include the question mark will result in a compiler error that looks like this:

  /tmp/test.pony:5:19: call is not partial but the method is - a question mark
  is required after this call
      /tmp/ponyc/packages/builtin/array.pony:578:24: method is here
        fun ref next(): B->A ? =>

See the RFC for more details: https://github.com/ponylang/rfcs/blob/master/text/0039-explicit-partial-calls.md

As you might imagine, this change will affect nearly every Pony codebase, so we want to provide support for developers who are making this transition.

We’ve created migration scripts for the convenience of developers making the transition. These scripts can ingest Pony compiler errors in the format emitted by ponyc to STDERR and make the necessary modifications to the Pony source code files that caused the errors, adding the question mark wherever it is needed for compliance with the new syntax requirement.

If you need any other assistance with this transition, please reach out to us. We’re here to help!


  • Fix compiler assertion failure on unused reference to _ (PR #2091)
  • Destroy all actors on runtime termination (PR #2058)
  • Fixed compiler segfault on empty triple quote comment. (PR #2053)
  • Fix compiler crash on exhaustive match where last case is a union subset (PR #2049)
  • Make pony_os_std_print() write a newline when given empty input. (PR #2050)
  • Fix boxed tuple identity when type identifiers differ (PR #2009)
  • Fix crash on interface function pointer generation (PR #2025)


  • Alpine Linux compatibility for pony (PR #1844)
  • Add cli package implementing the CLI syntax (RFC #38)
    • Initial (PR #1897) implemented the full RFC and contained:
      • Enhanced Posix / GNU program argument syntax.
      • Commands and sub-commands.
      • Bool, String, I64 and F64 option / arg types.
      • Help command and syntax errors with formatted output.
    • Update (PR #2019) added:
      • String-seq (ReadSeq[String]) types for repeated string options / args.
      • Command fullname() to make it easier to match on unique command names.
      • Checking that commands are leaves so that partial commands return syntax errors.


  • Forbid returning and passing tuples to FFI functions (PR #2012)
  • Deprecate support of Clang 3.3
  • Explicit partial calls - a question mark is now required to be at the call site for every call to a partial function.
    • See RFC 39.
    • Migration scripts for user code, for convenience, are provided here:


Sean T. Allen

Sean is a member of the Pony core team. His turn-ons include programming languages, distributed computing, Hiwatt amplifiers, and Fender Telecasters. His turn-offs include mayonnaise, stirring yogurt, and sloppy code. He is one of the authors of Storm Applied, and VP of Engineering at Wallaroo Labs.