Where you use like so: const double = x => x * 2 Ĭonst squaredDoubled = compose(square, double) Īnd doing squaredDouble(4) would return 32, I know this is a poor implementation of composition since it only support one argument and I know that Javascript does not return a function when you partially call another function, but I fear that having the notion of this^ implementation is what's tripping me up when trying to understand composition between functions that expect multiple arguments, would you mind ELI5 what happens internally when one composes things like (map. Haskell Language List Comprehensions Basic List Comprehensions Haskell has list comprehensions, which are a lot like set comprehensions in math and similar implementations in imperative languages such as Python and JavaScript. They should be distinct from (nested) for loops and the use of map and filter functions within the syntax of the language. It is similar to the way mathematicians describe sets, with a set comprehension, hence the name. As above, proposals have been made for comprehension. I read this as I need 3 arguments, two functions one initial value and I will produce a function c that needs you can call with any arguments, but what I can't wrap my head around is how does this work internally, I feel like my brain is betraying me since I'm used to implementing composition in Javascript like this: const compose = (.funcs) => arg => (funcs.reduce((composed, func) => func(composed), arg) A list comprehension is a special syntax in some programming languages to describe lists. Another common use-case is comprehensions (list/set/dict, and genexps). So in this case doing deepMap reverse, ] will return, ] and it kind of makes sense since it's a deep List, but my brain resist it because of map expect 2 arguments but returns a single value, I read the (.) operator info and this is it's annotation: (b -> c) -> (a -> b) -> a -> c But what's been throwing me off a little is when both functions expect multiple arguments such as this: deepMap :: (a -> b) -> ] -> ]
#Haskell list comprehension generator#
I you don't mind could you explain a little how composition of functions that expect multiple arguments work? there are things that are dead obvious like say: inspect :: -> Stringīoth unlines and show only expect one argument so the way I read this is xs is passed down to unlines and the returned value get's passed show which also expect a single argument. List comprehension in Haskell is a way to produce the list of new elements from the generator we have passed inside it. So I figured I could use a simple comprehension and recursion like so: buildGrid :: Num a => -> -> ]īuildGrid (r:rs) cs = -> -> ]īuildGrid rs cs = [[(r, c) | c m1 a -> m2 b -> m1 (m2 (a, b))) I was immediately filled with questions, which do you think is the best answer? or can you provide a better one? why? I recently started learning haskell, and there was this exercise where I had to build a grid of coordinates using tuples, something like this: