Common module types like ANY, SORTABLE, ...
module type ANY = sig ... endCan be any type.
module type SORTABLE = sig ... endA sortable type is a type with a comparison function.
module type FUNCTOR = sig ... endA functor is an abstract container which is mappable
module type APPLICATIVE = sig ... endAn applicative functor is an abstract container which is mapable and if it has functions in it the functios can be applied.
module type MONAD0 = sig ... endA minimal monad signature.
module type MONAD = sig ... endA monad is an applicative functor with a bind >>= operator.
module type READABLE = sig ... endReadable structure
module type WRITABLE = sig ... endWritable structure