Glad you made it! :)
Haskell is a very extensible programming language, some users even write extensions for the compiler (kind of like Chrome plugins) that do awesome stuff. Tidal leverages these extensions.
What is a pattern in Tidal? Is it something by itself like keywords or special syntax? Not really. Is it a string? Nope. But it looks like a string!
OverloadedStrings we tell the compiler to treat stuff that looks like a string like another thing we’d like (in this case, a pattern) and viceversa.