undefined | Better HN

0 pointssomenewacc7y ago0 comments

But comprehensions are also a functional idiom.

0 comments

Yeah, sorry, I didn't mean to say that Python's not functional without a "map" function. More trying to guess where that perception comes from. Python's comprehensions are (I believe) inspired by Haskell, but, if you're not a Haskeller, you're probably more used to other ways of doing things.

lmm7y ago

The version Python has is awkward to work with, to the point that many Haskell programmers don't even realise it exists. The "do notation" style is much clearer than the "comprehension" style; unfortunately Python has no equivalent.

bad_user7y ago

FP means referential transparency. For-comprehensions operate on iterators and iterators are not FP, being a very dirty and mutable protocol.

Do not confuse FP with declarative programming or with laziness. FP often implies declarative APIs and laziness but not vice-versa.

duckerude7y ago

Python's comprehensions were lifted from Haskell, and its map and filter functions also operate on iterables. They can't be purely functional because of the surrounding language, but they do follow a functional style.

(expr for item in iterable if cond) is more or less another way to spell map(lambda item: expr, filter(lambda item: cond, iterable)), except readable.

You could define "functional programming" to absolutely require referential transparency, but that's not what the rest of the thread is doing.

kthielen7y ago

I don't mean to be pedantic but IIRC Python's comprehensions actually came from the SETL language.

Obviously it's ultimately the same thing either way, but that's the lineage (SETL -> ABC -> Python).

https://en.wikipedia.org/wiki/SETL

duckerude7y ago

I didn't know about SETL, that's interesting.

https://docs.python.org/3/howto/functional.html#generator-ex... claims Python borrowed them from Haskell, but the ABC link seems more likely.

1 more reply

j / k navigate · click thread line to collapse

0 comments

bunderbunder7y ago

lmm7y ago

bad_user7y ago

FP means referential transparency. For-comprehensions operate on iterators and iterators are not FP, being a very dirty and mutable protocol.

Do not confuse FP with declarative programming or with laziness. FP often implies declarative APIs and laziness but not vice-versa.

duckerude7y ago

(expr for item in iterable if cond) is more or less another way to spell map(lambda item: expr, filter(lambda item: cond, iterable)), except readable.

You could define "functional programming" to absolutely require referential transparency, but that's not what the rest of the thread is doing.

kthielen7y ago

I don't mean to be pedantic but IIRC Python's comprehensions actually came from the SETL language.

Obviously it's ultimately the same thing either way, but that's the lineage (SETL -> ABC -> Python).

https://en.wikipedia.org/wiki/SETL

duckerude7y ago

I didn't know about SETL, that's interesting.

https://docs.python.org/3/howto/functional.html#generator-ex... claims Python borrowed them from Haskell, but the ABC link seems more likely.

1 more reply

j / k navigate · click thread line to collapse