Haskell：列表理解是高阶函数吗？

Question

我有一个我们不应该使用任何更高阶函数的赋值，列表理解是否可以归类为更高阶函数？

Answer 1

A list comprehension in Haskell is just syntactic sugar. It is defined in the Haskell 2010 Report here like so:

[ e | True ]          = [e]
[ e | q ]             = [ e | q, True ]
[ e | b, Q  ]         = if b then [ e | Q ] else []
[ e | p <- l, Q ]     = let ok p = [ e | Q ]
                            ok _ = []
                        in concatMap ok  l
[ e | let decls, Q ]  = let decls in [ e | Q ]

Note the use of Q , which ranges over qualifiers (which can include functions), in the patterns. So the answer is yes, a list comprehension is higher-order.

Answer 2

”Higher order" has a specific meaning. If a function takes an argument which is a function (or returns a function), the former is said to be higher order. (For example: map.)

List comprehensions are expressions representing list values, not functions. So the answer is: No.