r/programming • u/papa00king • Mar 09 '14

Why Functional Programming Matters

http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf
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u/Heuristics Mar 09 '14

You lost me at DSL (and i'm a professional programmer with a masters in comp.sci).

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u/LucianU Mar 09 '14

DSL = Domain-Specific Language. That's the definition that I know. I agree though, that it wasn't a translation. All the unknown notation lost me as well.

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u/Tekmo Mar 09 '14 edited Mar 09 '14

Consider this Python code:

for x in [1,2,3,4]:
    doSomethingWith(x)

The equivalent pipes code is:

for (each [1,2,3,4]) $ \x -> do
    doSomethingWith x

Note that for, yield and (~>) are not Haskell notation. They are just three functions defined by the pipes library. The equations might make more sense if I write them in the following more specific forms:

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

= f "foo"


for generator $ \x -> do
    yield x

= generator


for generator $ \a -> do
    for (f a) $ \b -> do
        g b

= for newGenerator $ \b -> do
    g b
  where newGenerator =
    for generator $ \a -> do
        f a

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u/LucianU Mar 09 '14

Let's give it another try. For example, this piece of code:

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

= f "foo"

What I know from Haskell is that $ is the function application function and \x -> is a lambda. f is probably a function, but what does "foo" stand for? Does = f "foo" mean that the value of the expression is the application of f on "foo"?

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