in which the haskell community totally does my homework for me

joeyh at 2014-09-25T06:25:41Z

http://stackoverflow.com/questions/26027765/using-types-to-prevent-conflicting-port-numbers-in-a-list

type-level prevention of port conflicts, here propellor comes!

I'm looking forward to that day when successfully compiling a Propellor config will be sufficent to guarantee the server will work, and one will never actually have to deploy it at all.

Oh, wait...

Olivier Mehani at 2014-09-25T06:30:11Z

I'm just astounded that a) this can be done, type level unique list checking and all and b) someone did it in response to a 5 minute question and c) at the beautiful beautiful type error message

Couldn't match type 'False with 'True
    Expected type: 'True
      Actual type: ServiceTypes.UniquePorts '[443, 80, 443]

Aka

Hey dude, you can't run a tor bridge and a web server on the same host
(given their default configurations)

We're truely living in the future of programming... well, some of us are, some of the time. Rest of us are patching bash. :)

joeyh at 2014-09-25T06:32:49Z

Raúl Benencia likes this.

I think I'll be able to improve the type error message some too, along the lines of "Couldn't match type PortConflicts with SanePorts"

joeyh at 2014-09-25T06:37:04Z

Indeed, without reading the code the error message is pretty cryptic. It was an interesting reading. I didn't know that GHC could do that at all.

Raúl Benencia at 2014-09-25T14:48:01Z