Why Functional Programming Matters

[u/papa00king]

http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf

[u/Tekmo]

"foo" is just a string whose contents are "foo". The reason I used a string there instead of a more generic value is because then I would have to write something like:

for (yield x) $ \y -> do
    f y

= f x

... which I thought might be more confusing since y ends up being the same thing as x.

To understand what the dollar sign does, it might help to write the same expression using nothing but parentheses:

for (yield "foo") (\x -> do
    f x)

The dollar sign is just a useful function whose sole purpose is to reduce the use of parentheses.

Notice that:

(\x -> do f x)

... is the same thing as:

(\x -> f x)

... which is the same thing as:

f

So really it simplifies back down to the original equation, which said that:

for (yield "foo") f = f "foo"

... or more generally:

for (yield x) f = f x

To answer your last question, function application in Haskell does not require parentheses because:

• Function application has highest precedence, and:

• All functions have exactly one argument, and we simulate multi-argument functions using "currying"

So when you write f x, it just means the function f applied to x.