[Haskell-cafe] Where does ~> come from?

[Steve Lihn]

While I am reading TypeCompose module, I am having trouble finding
where ~> comes from? (And its son ~~> and grandson ~~~>, etc.)  This
is my immediate question. Help is appreciated.

A bigger (higher-order?) issue I encountered and I think other people
could also have is to look up all these special "symbols" during the
learning curve. As things are getting higher and higher order in
Haskell, more inventive symbols are appearing. It becomes harder to
remember the exact definitions are. The difficulties are:

1) I used to see a page on haskell.org that lists many symbols, but I
could not find that page any more.
2) You would hope there is a quick way to search those symbols. But
most search engines do not treate symbols friendly, often just ignore
them. I typed ~> in Hoogle, it also returned nothing.
3) If the module defining the symbol is not in standard library, it is
not possible to look up the symbol in the core library index.

The only way to find the symbol seems to go to the source code, check
every module being imported and if I am lucky I will find it in the
same package. If  I am not lucky, I will have to search that module on
the Internet, and hunt it down recursively.

I wonder if anybody has the same problem. If enough crowd have the
same problem, maybe there could be a better way to handle this kind of
documentation/learning issue!

Thanks,
Steve