What's the difference between GHC and the Haskell Platform?

Question

I'm about to get into Haskell, and I'm a bit confused why I'm recommended to install both GHC and the Haskell-platform via brew.

Isn't GHC a Haskell implementation/compiler?
When does one need the platform?

Answer 1

Short answer:
The Haskell Platform is a collection of stuff.
GHC is one specific component of those stuff.

Longer answer:
Usually you want to install the Haskell Platform, because then you get lots of stuff installed all in one go as opposed to having to manually set up all the pieces one at a time.
That's the purpose of the Haskell Platform.

To give some historical perspective: before the Haskell Platform was invented, GHC itself used to come with a random grab-bag of libraries.
The Haskell Platform was invented so that somebody less overworked could decide which libraries should and shouldn't be included out of the box (i.e. so the GHC people could stop thinking about libraries and go back to thinking about GHC).
It's been quite successful in that respect.

Answer 2

The Haskell Platform is a collection of compilers, tools and libraries for Haskell.

It currently specifies that GHC is included in the platform.

Compliant Haskell Platform packages will install GHC without additional work required on the part of the user.