what is the meaning of "let x = x in x" and "data Float#" in GHC.Prim in Haskell

Question

I looked at the module of GHC.Prim and found that it seems that all datas in GHC.Prim are defined as data Float# without something like =A|B, and all functions in GHC.Prim is defined as gtFloat# = let x = x in x.

My question is whether these definations make sense and what they mean.

I checked the header of GHC.Prim like below

{-
This is a generated file (generated by genprimopcode).
It is not code to actually be used. Its only purpose is to be
consumed by haddock.
-}

I guess it may have some relations with the questions and who could please explain that to me.

Answer 1

It's magic :)

These are the "primitive operators and operations". They are hardwired into the compiler, hence there are no data constructors for primitives and all functions are bottom since they are necessarily not expressable in pure haskell.

(Bottom represents a "hole" in a haskell program, an infinite loop or undefined are examples of bottom)

To put it another way

These data declarations/functions are to provide access to the raw compiler internals. GHC.Prim exists to export these primitives, it doesn't actually implement them or anything (eg its code isn't actually useful). All of that is done in the compiler.

It's meant for code that needs to be extremely optimized. If you think you might need it, some useful reading about the primitives in GHC