What is the difference between . (dot) and $ (dollar sign)?

Question

What is the difference between the dot (.) and the dollar sign ($)?

As I understand it, they are both syntactic sugar for not needing to us

Answer 1

($) allows functions to be chained together without adding parentheses to control evaluation order:

Prelude> head (tail "asdf")
's'

Prelude> head $ tail "asdf"
's'

The compose operator (.) creates a new function without specifying the arguments:

Prelude> let second x = head $ tail x
Prelude> second "asdf"
's'

Prelude> let second = head . tail
Prelude> second "asdf"
's'

The example above is arguably illustrative, but doesn't really show the convenience of using composition. Here's another analogy:

Prelude> let third x = head $ tail $ tail x
Prelude> map third ["asdf", "qwer", "1234"]
"de3"

If we only use third once, we can avoid naming it by using a lambda:

Prelude> map (\x -> head $ tail $ tail x) ["asdf", "qwer", "1234"]
"de3"

Finally, composition lets us avoid the lambda:

Prelude> map (head . tail . tail) ["asdf", "qwer", "1234"]
"de3"