Can someone explain me how I should understand Semigroup?

fantasy-land/concat :: Semigroup a => a ~> a -> a

Since there are so many as, it’s quite confusing though I’ve read the documentation. Can someone provide me an actual example please?

[CrossEye]

@jujoba: There’s a typo in the second bullet.

• a ~> means: The following function is a method of an a (chain is a method of an instance that has a Semigroup)

should read

• a ~> means: The following function is a method of an a (concat is a method of an instance that has a Semigroup)

[davidchambers]

Here are some examples, using S.concat:

> S.concat ('abc') ('def')
'abcdef'

> S.concat ([1, 2, 3]) ([4, 5, 6])
[1, 2, 3, 4, 5, 6]

> S.concat ({x: 1, y: 2}) ({y: 3, z: 4})
{x: 1, y: 3, z: 4}

> S.concat (S.Just ([1, 2, 3])) (S.Just ([4, 5, 6]))
Just ([1, 2, 3, 4, 5, 6])

> S.concat (Sum (18)) (Sum (24))
Sum (42)

S.concat is easier to understand than the underlying fantasy-land/concat methods for several reasons:

• its type signature does not contain a squiggly arrow (~>);
• it does not reference fantasy-land/concat explicitly; and
• it works for some built-in types such as String, even though String.prototype['fantasy-land/concat'] is undefined.

Here is an example of invoking a fantasy-land/concat method directly:

> S.Just ('abc') ['fantasy-land/concat'] (S.Just ('def'))
Just ('abcdef')