Class of all Abelian ({i.e.}, commutative) monoids that satisfy the commutativity property:

a <> b == b <> a

Class of Abelian monoids with a partial inverse for the Monoid <> operation. The inverse operation </> must satisfy the following laws:

maybe a (b <>) (a </> b) == a
maybe a (<> b) (a </> b) == a

Subclass of ReductiveMonoid where </> is a complete inverse of the Monoid <> operation. The class instances must satisfy the following additional laws:

(a <> b) </> a == Just b
(a <> b) </> b == Just a

Class of Abelian monoids that allow the greatest common denominator to be found for any two given values. The operations must satisfy the following laws:

gcd a b == commonPrefix a b == commonSuffix a b
Just a' = a </> p && Just b' = b </> p
   where p = gcd a b

If a GCDMonoid happens to also be a CancellativeMonoid, it should additionally satisfy the following laws:

gcd (a <> b) (a <> c) == a <> gcd b c
gcd (a <> c) (b <> c) == gcd a b <> c

Class of monoids with a left inverse of mappend, satisfying the following law:

isPrefixOf a b == isJust (stripPrefix a b)
maybe b (a <>) (stripPrefix a b) == b
a `isPrefixOf` (a <> b)

| Every instance definition has to implement at least the stripPrefix method. Its complexity should be no worse than linear in the length of the prefix argument.

Class of monoids with a right inverse of mappend, satisfying the following law:

isSuffixOf a b == isJust (stripSuffix a b)
maybe b (<> a) (stripSuffix a b) == b
b `isSuffixOf` (a <> b)

| Every instance definition has to implement at least the stripSuffix method. Its complexity should be no worse than linear in the length of the suffix argument.

Subclass of LeftReductiveMonoid where stripPrefix is a complete inverse of <>, satisfying the following additional law:

stripPrefix a (a <> b) == Just b

Subclass of LeftReductiveMonoid where stripPrefix is a complete inverse of <>, satisfying the following additional law:

stripSuffix b (a <> b) == Just a

Class of monoids capable of finding the equivalent of greatest common divisor on the left side of two monoidal values. The methods' complexity should be no worse than linear in the length of the common prefix. The following laws must be respected:

stripCommonPrefix a b == (p, a', b')
   where p = commonPrefix a b
         Just a' = stripPrefix p a
         Just b' = stripPrefix p b
p == commonPrefix a b && p <> a' == a && p <> b' == b
   where (p, a', b') = stripCommonPrefix a b

Class of monoids capable of finding the equivalent of greatest common divisor on the right side of two monoidal values. The methods' complexity must be no worse than linear in the length of the common suffix. The following laws must be respected:

stripCommonSuffix a b == (a', b', s)
   where s = commonSuffix a b
         Just a' = stripSuffix p a
         Just b' = stripSuffix p b
s == commonSuffix a b && a' <> s == a && b' <> s == b
   where (a', b', s) = stripCommonSuffix a b