[olliej]

Something that I always found funny is that main clearly has to take something as input (otherwise it would not be able to produce different output between runs). So in GHC the main method (main :: IO()) internally takes a value of type RealWorld (theRealWorld) and returns the new RealWorld produced by running the program. I imagine by the time it's lowered to actual assembly they've dropped that, but I've never dealt with ghc's machine codegen

[shirogane86x]

I am not at all an expert on GHC's codegen, but having glanced at that code before (mostly to get an intuition of what IO is under all that sugar), RealWorld doesn't even... exist. Realworld and its close friend, State# are tokens of sort. they're zero-sized and deeply magical (the GHC.Prim is quite enlightening to read). All the primops are defined as infinite loops... it's quite a sight to behold. As something totally unrelated to the above, a lot of the more internal GHC stuff (so the GHC.* modules, the stdlib/base, etc) are in my opinion readable and most of all, well commented, so it's quite fun to take a look sometimes.

[olliej]

Oh of course - I only ever worked with the GHC Core language which is completely and explicitly typed so it was especially blatant :D

I do understand that in reality it's simply a tag value to ensure that the compiler correctly orders and threads operations correctly, but I still think it's semantically cute :D