function-composition

问题 This is more a kind of theoretical question. Is it possible in C++11 to combine functions into a new function? For example : auto f = [](int i){return i * 2;}; auto g = [](int i){return i + 10;}; So this works: auto c = f(g(20)); // = 60 But I want an object that stores the combination, like auto c = f(g); std::cout << c(20) << std::endl; //prints 60 Edit: Additionally what i want to create is a function a, which you can give a function b and an int n , and which returns the n'th combination

问题 This code does NOT work: def inc(x): return x + 1 def repeat(f, n): if n == 0: return lambda x: x else: return f( repeat(f, n - 1 ) ) inc_10 = repeat(inc, 10) #TypeError: unsupported operand type(s) for +: 'function' and 'int' ''' # Ideally print(inc_10(0)) # 10 ''' How can I write it in a more Pythonic way or in lambda calculus way ? 回答1: You still need to return a function, not the result of calling f , in the recursive case. # repeat :: (a -> a) -> Integer -> a -> a # repeat _ 0 = id #

问题 This code does NOT work: def inc(x): return x + 1 def repeat(f, n): if n == 0: return lambda x: x else: return f( repeat(f, n - 1 ) ) inc_10 = repeat(inc, 10) #TypeError: unsupported operand type(s) for +: 'function' and 'int' ''' # Ideally print(inc_10(0)) # 10 ''' How can I write it in a more Pythonic way or in lambda calculus way ? 回答1: You still need to return a function, not the result of calling f , in the recursive case. # repeat :: (a -> a) -> Integer -> a -> a # repeat _ 0 = id #

来源： https://stackoverflow.com/questions/34701011/how-to-manually-infer-the-type-of

来源： https://stackoverflow.com/questions/14707720/haskell-why-is-f-g-equal-to-f-g-x

问题 What is wrong with this function? It seems like a scope error (although I thought I had fixed that by placing each callable in the list, instead of using it directly). Error is max recursion depth reached (when calling comp(inv,dbl,inc))... Note: the question is: why is it even recursing, not why it's reaching the max depth... def comp(*funcs): if len(funcs) in (0,1): raise ValueError('need at least two functions to compose') # get most inner function composed = [] print("appending func 1")

问题 What is wrong with this function? It seems like a scope error (although I thought I had fixed that by placing each callable in the list, instead of using it directly). Error is max recursion depth reached (when calling comp(inv,dbl,inc))... Note: the question is: why is it even recursing, not why it's reaching the max depth... def comp(*funcs): if len(funcs) in (0,1): raise ValueError('need at least two functions to compose') # get most inner function composed = [] print("appending func 1")

问题 I'm writing a macro for function / macro composition (mixed combinations are possible). Inside of the macro I have to treat symbols which represent functions and those that name macros differently. It is because result function must work with any number of arguments (if 'lowest' function in composition can), and I cannot apply apply to macros. My question: how to determine what a given symbol represents: function or macro? 回答1: Macro: CL-USER 8 > (macro-function 'bar) NIL CL-USER 9 > (macro

问题 It's fairly straightforward to write a function that composes two other functions. (For simplicity, assume they are one parameter each.) def compose(f, g): fg = lambda x: f(g(x)) return fg def add1(x): return x + 1 def add2(x): return x + 2 print(compose(add1, add2)(5)) # => 8 I would like to do composition using an operator, e.g., (add1 . add2)(5) . Is there a way to do that? I tried various decorator formulations, but I couldn't get any of them to work. def composable(f): """ Nothing I

问题 Live code example I'm trying to learn transducers via egghead and I think I got it until we try to compose object transformation. I have an example below that doesn't work const flip = map(([k,v]) => ({[v]: k})); const double = map(([k,v]) => ({[k]: v + v})); seq(flip, {one: 1, two: 2}); /*?*/ {1: 'one', 2: 'two'} seq(double, {one: 1, two: 2}); /*?*/ {'one': 2, 'two: 4} but if I compose it fails: seq(compose(flip, double), {one: 1, two: 2}); /*?*/ {undefined: NaN} seq(compose(double, flip),