小编Kyl*_*ean的帖子

import Control.Monad (liftM2)

infixl 4 :+:, :-: 
infixl 5 :*:, :/:

data Expr a  = Const a 
         | (Expr a) :+: (Expr a) 
         | (Expr a) :-: (Expr a)
         | (Expr a) :*: (Expr a)
         | (Expr a) :/: (Expr a)
         deriving (Show, Eq)

evalExpr (Const a) = a 
evalExpr (a :+: b) = liftM2 (+) (evalExpr a) (evalExpr b)
evalExpr (a :-: b) = liftM2 (-) (evalExpr a) (evalExpr b)
evalExpr (a :*: b) = liftM2 (*) (evalExpr a) …

这是我的第一次尝试:

import java.util.function.*;
import java.util.ArrayList;
public class IO<A> {
    private Function<World,Tuple<World,A>> transform;
    private class World {
        private ArrayList<String> stdin;
        private ArrayList<String> stdout;
        public World() {
            this.stdin  = new ArrayList<String>();
            this.stdout = new ArrayList<String>();
        }
    }
    private class Tuple<F,S> {
        public F fst;
        public S snd;
        public Tuple(F fst, S snd) {
            this.fst = fst;
            this.snd = snd;
        }
    }
    public IO(Function<World,Tuple<World,A>> transform) {
        this.transform = transform;
    }
    public IO<A> pure(A a) {
        return new IO<A>(r -> new Tuple<World,A>(r,a));
    }
    public …

我试图实现一个简单类型的lambda演算类型检查器.运行完整性测试时,我尝试输入(SKK),我的类型检查器抛出此错误:

TypeMismatch {firstType = t -> t, secondType = t -> t -> t}

违规术语显然是(SKK)

(\x:t -> t -> t.\y:t -> t.\z:t.x z (y z)) (\x:t.\y:t.x) (\\x:t.\y:t.x)

我认为问题源于缺乏多态性,因为当我输入检查这个haskell代码时它工作正常:

k x y = x
s x y z = x z (y z)
test = s k k -- type checks

但如果我专注于这种类型:

k :: () -> () -> ()
k x y = x
s :: (() -> () -> ()) -> (() -> ()) -> () -> ()
s x …

我试图模拟e ^ x的泰勒多项式

---Macularian for e^x 
e :: (Num a) => a -> Int -> a
e value precsion = sum $ take precsion [((x^n) / product [1..n]) | x <- value, n <- [0..]]

这是我的错误

Main.hs@3:73-3:78不能从e :: Num a => a - > Int - > a的类型签名绑定的上下文(Num a)中推断出(a~ [a]) home/app/isolation-runner-work/projects/75872/session.207/src/Main.hs:2:6-29 a是一个刚性类型变量,由e :: Num a => a的类型签名绑定> Int - > a at /home/app/isolation-runner-work/projects/75872/session.207/src/Main.hs:2:6相关绑定包括value :: a(绑定在/ home/app/isolation -runner-works/projects/75872/session.207/src/Main.hs:3:3)e :: a - > Int - > a(绑定在/ home/app/isolation-runner-work/projects/75872 /session.207/src/Main.hs:3:1)...