Nested lambdas can't auto-capture free references from the outer scope.

[jemc]

As of #1648, the following works:

actor Main
  new create(env: Env) =>
    {() =>
      env.out.print("Hello, world!")
    }()

Building builtin -> /home/jemc/1/code/gitx/ponyc/packages/builtin
Building . -> /home/jemc/1/code/gitx/ponyc/test.jemc
Generating
 Reachability
 Selector painting
 Data prototypes
 Data types
 Function prototypes
 Functions
 Descriptors
Optimising
Writing ./test.jemc.o
Linking ./test.jemc
Hello, world!

But the following doesn't:

actor Main
  new create(env: Env) =>
    {() =>
      {() =>
        env.out.print("Hello, world!")
      }()
    }()

Building builtin -> /home/jemc/1/code/gitx/ponyc/packages/builtin
Building . -> /home/jemc/1/code/gitx/ponyc/test.jemc
Error:
/home/jemc/1/code/gitx/ponyc/test.jemc/test.pony:6:9: cannot capture "env", variable not defined
        env.out.print("hello world")
        ^
Error:
/home/jemc/1/code/gitx/ponyc/test.jemc/test.pony:6:9: can't find declaration of 'env'
        env.out.print("hello world")

If lambdas can automatically capture free references from the immediately surrounding scope, I'd expect (principle of least surprise) that they can also do so with free references from an outer scope surrounding that scope, with the surrounding scope being made to capture the reference intermediately.

That is, I'd expect this to happen implicitly:

actor Main
  new create(env: Env) =>
    {()(env) =>
      {()(env) =>
        env.out.print("Hello, world!")
      }()
    }()

[jemc]

Discussed on sync call - @sylvanc agrees it should work, and it's an implementation bug.

[jemc]

Adding the needs discussion tag here so we can check the status of this during the next sync call.

[SeanTAllen]

I wasn't aware this issue existed.

[SeanTAllen]

@sylvanc any progress on this?