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If anything, functional programming gives you too many ways to achieve the same thing. How many ways can a reasonable programmer write the factorial function i

by verroq 14y ago

If anything, functional programming gives you too many ways to achieve the same thing. How many ways can a reasonable programmer write the factorial function imperatively (without using the closed form formula or any dynamic programming). A maximum of two. A for loop or use recursion. But just look at how many ways you could write factorial in a functional programming language. http://www.willamette.edu/~fruehr/haskell/evolution.html http://www.willamette.edu/~fruehr/haskell/evolution.html It is truly unfortunate when your ability to program functionally is directly proportional to how much of the standard library you have memorised. This makes functional programming much harder to learn. edit: I don't really care if you downvote. I come here discuss programming.

glassx 14y ago
> How many ways can a reasonable programmer write the factorial function imperatively This page is a terrible example. Most of these are not not what a "reasonable programmer" would do. An unreasonable programmer would be able to screw up on any paradigm. You'd probably have even more ways to screw up like this with an OO language, creating classes for recursive functions, trampolines, a pattern matching class, implement an language interpreter inside your factorial implementation, etc.
- verroq 14y ago
  > You'd probably have even more ways to screw up like this with an OO language My example was about imperative languages. You assertion on how many ways one could screw up on OO is irrelevant and besides, you'd really need a good understanding of OO to even try implementing those. I didn't mean to use to imply any of those methods were bad. I have revised my post so people can't miss the point. That is > It is unfortunate when your ability to program functionally is directly proportional to how much of the standard library you have memorised. This makes functional programming much harder to learn. Now, addressing your concerns. > This page is a terrible example. Most of these are not not what a "reasonable programmer" would do. All of the examples except for few particularly egregious ones seems reasonable to me. For example -- one, need n+k patterns but so what fac 0 = 1 fac (n+1) = (n+1) * fac n -- two fac 0 = 1 fac n = n * fac (n-1) -- three fac n = foldl (*) 1 [1..n] -- four facs = scanl (*) 1 [1..] fac n = facs !! n -- five fac = foldr (*) 1 . enumFromTo 1 -- six fac n = product [1..n] Six fairly distinctive ways. I'm sure there's more that's as elegant if not more elegant ways to do the same thing.
  - jwdunne 14y ago
    After the first 2, the rest are based on common and very useful abstractions. You could translate those to an OO language quite easily too, though with a lot more code. For example, what foldl does, from my understanding, is to recursively apply a function to both a starting value and the first element of a list, and then the same thing again, where the result from the last call becomes the starting value and the rest of the list becomes the list we're working on, up until the list is empty. Not sure if I've explained this well but I've not been into this long. If you see the second function, that's what it's doing, except it's working just with numbers and not a list. Since foldl works on lists, you need an enumerator, which in this case is just 1 through to n. The sixth example is great here. Product could easily be an abstraction on something quite similar to three, which itself could very well be an abstraction quite similar to two (using lists, functions to deal with lists and a given function). Please correct me if I'm wrong at any point here. I'm looking to improve these skills quite a lot so it'd be very, very welcome.
    - Dn_Ab 14y ago
      You got the core, I will correct your edges. The [1..3] is just sugar for 1:2:3:[] Product is not actually an abstraction as it's restricted to work on number types. And no foldl is not an abstraction of (2) because foldl is tail recursive while (2) is not. foldr is not tail recursive however and combined with haskell's laziness can make short work of infinite lists. But you are right in that any tail recursive function on a list can be rewritten using foldl. What is particular to haskell vs a strict language like say F# is that foldl can still pop a stack due to haskell's laziness. You want foldl' as it will force the initial argument. Fold is also a fundamental operation on any algebraic data structure such as trees , lists, and natural numbers. You can write filter, map, filtermap etc in terms of it for example. There is so much to say about fold - they are like the cupboard which leads to narnia.. but I will stop now so as not to turn this into an infodump.
      - jwdunne 14y ago
        Oh wow, thanks! I should have also noted I have no experience with the language in the examples so please ignore any ignorance there (probably should have read up on it). Interesting! All well noted and I'll look into this more. I'm vaguely aware of fold's power and can definitely see how filter, map and the likes would be implemented in terms of it but I would be really interested in the infodump! I'm just wondering, ignoring laziness and typing (or any language-specifics), if foldl could be written similar to (2)? Obviously it wouldn't be very good. I've written an example in Racket of what I have in mind: (define (foldl fn initial lst) (if (null? lst) initial (fn (car lst) (foldl fn initial (cdr lst))))) (define (fac n) (if (= n 0) 1 (* n (fac (- n 1))))) (= (fac 3) (foldl * 1 '(1 2 3))) Thanks again for the info, really appreciated. :)
viscanti 14y ago
This list is a joke, based on a similar list for imperative programmers writing a "hello world" program. There are certainly a number of ways to write write something in either paradigm. The number of ways you can write something is a horrible metric to evaluate languages on. Any sufficiently clever programmer can come up with a number of bad solutions. The useful imperative techniques are more obvious to you because you have more experience with that framework. Experienced functional programmers would just as quickly narrow their list of useful solutions. In order to be productive in a functional style, you don't need to know much of the language's standard library. You simply write small functions that can be applied in a number of areas. You'll probably end up re-inventing the wheel though, as most functional languages come with most of the essential functional constructs included in the standard library. If anything, functional programming is more beginner friendly, because you don't end up dealing with mutable state and you can easily work on the level of abstraction that you're most comfortable with (you're just composing ever more advanced functions from simpler ones).
ufo 14y ago
BTW, since we are takling a bout Haskell, an interesting thing I noticed about it is that precisely I don`t need to memorize the whole standard library. Whenever I have a though like "man, I whished that there was a function that gor me a Bar from this list of Foos" I can just pass the "[Foo] -> Bar" type to Hoogle[1] and it will magically find the name of all the functions in the standard libraries that have compatible or similar type signatures. [1] http://www.haskell.org/hoogle/ http://www.haskell.org/hoogle/

by verroq 14y ago

glassx 14y ago

> How many ways can a reasonable programmer write the factorial function imperatively This page is a terrible example. Most of these are not not what a "reasonable programmer" would do. An unreasonable programmer would be able to screw up on any paradigm. You'd probably have even more ways to screw up like this with an OO language, creating classes for recursive functions, trampolines, a pattern matching class, implement an language interpreter inside your factorial implementation, etc.

verroq 14y ago
> You'd probably have even more ways to screw up like this with an OO language My example was about imperative languages. You assertion on how many ways one could screw up on OO is irrelevant and besides, you'd really need a good understanding of OO to even try implementing those. I didn't mean to use to imply any of those methods were bad. I have revised my post so people can't miss the point. That is > It is unfortunate when your ability to program functionally is directly proportional to how much of the standard library you have memorised. This makes functional programming much harder to learn. Now, addressing your concerns. > This page is a terrible example. Most of these are not not what a "reasonable programmer" would do. All of the examples except for few particularly egregious ones seems reasonable to me. For example -- one, need n+k patterns but so what fac 0 = 1 fac (n+1) = (n+1) * fac n -- two fac 0 = 1 fac n = n * fac (n-1) -- three fac n = foldl (*) 1 [1..n] -- four facs = scanl (*) 1 [1..] fac n = facs !! n -- five fac = foldr (*) 1 . enumFromTo 1 -- six fac n = product [1..n] Six fairly distinctive ways. I'm sure there's more that's as elegant if not more elegant ways to do the same thing.
- jwdunne 14y ago
  After the first 2, the rest are based on common and very useful abstractions. You could translate those to an OO language quite easily too, though with a lot more code. For example, what foldl does, from my understanding, is to recursively apply a function to both a starting value and the first element of a list, and then the same thing again, where the result from the last call becomes the starting value and the rest of the list becomes the list we're working on, up until the list is empty. Not sure if I've explained this well but I've not been into this long. If you see the second function, that's what it's doing, except it's working just with numbers and not a list. Since foldl works on lists, you need an enumerator, which in this case is just 1 through to n. The sixth example is great here. Product could easily be an abstraction on something quite similar to three, which itself could very well be an abstraction quite similar to two (using lists, functions to deal with lists and a given function). Please correct me if I'm wrong at any point here. I'm looking to improve these skills quite a lot so it'd be very, very welcome.
  - Dn_Ab 14y ago
    You got the core, I will correct your edges. The [1..3] is just sugar for 1:2:3:[] Product is not actually an abstraction as it's restricted to work on number types. And no foldl is not an abstraction of (2) because foldl is tail recursive while (2) is not. foldr is not tail recursive however and combined with haskell's laziness can make short work of infinite lists. But you are right in that any tail recursive function on a list can be rewritten using foldl. What is particular to haskell vs a strict language like say F# is that foldl can still pop a stack due to haskell's laziness. You want foldl' as it will force the initial argument. Fold is also a fundamental operation on any algebraic data structure such as trees , lists, and natural numbers. You can write filter, map, filtermap etc in terms of it for example. There is so much to say about fold - they are like the cupboard which leads to narnia.. but I will stop now so as not to turn this into an infodump.
    - jwdunne 14y ago
      Oh wow, thanks! I should have also noted I have no experience with the language in the examples so please ignore any ignorance there (probably should have read up on it). Interesting! All well noted and I'll look into this more. I'm vaguely aware of fold's power and can definitely see how filter, map and the likes would be implemented in terms of it but I would be really interested in the infodump! I'm just wondering, ignoring laziness and typing (or any language-specifics), if foldl could be written similar to (2)? Obviously it wouldn't be very good. I've written an example in Racket of what I have in mind: (define (foldl fn initial lst) (if (null? lst) initial (fn (car lst) (foldl fn initial (cdr lst))))) (define (fac n) (if (= n 0) 1 (* n (fac (- n 1))))) (= (fac 3) (foldl * 1 '(1 2 3))) Thanks again for the info, really appreciated. :)

viscanti 14y ago

This list is a joke, based on a similar list for imperative programmers writing a "hello world" program. There are certainly a number of ways to write write something in either paradigm. The number of ways you can write something is a horrible metric to evaluate languages on. Any sufficiently clever programmer can come up with a number of bad solutions. The useful imperative techniques are more obvious to you because you have more experience with that framework. Experienced functional programmers would just as quickly narrow their list of useful solutions. In order to be productive in a functional style, you don't need to know much of the language's standard library. You simply write small functions that can be applied in a number of areas. You'll probably end up re-inventing the wheel though, as most functional languages come with most of the essential functional constructs included in the standard library. If anything, functional programming is more beginner friendly, because you don't end up dealing with mutable state and you can easily work on the level of abstraction that you're most comfortable with (you're just composing ever more advanced functions from simpler ones).

ufo 14y ago

BTW, since we are takling a bout Haskell, an interesting thing I noticed about it is that precisely I don`t need to memorize the whole standard library. Whenever I have a though like "man, I whished that there was a function that gor me a Bar from this list of Foos" I can just pass the "[Foo] -> Bar" type to Hoogle[1] and it will magically find the name of all the functions in the standard libraries that have compatible or similar type signatures. [1] http://www.haskell.org/hoogle/ http://www.haskell.org/hoogle/