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Type Parameter Unification


Type Parameter Unification

By : Abner Figueiredo
Date : October 28 2020, 08:00 PM
seems to work fine Why is this disallowed in C#? alt text http://img706.imageshack.us/img706/7360/restriction.png , The first reason that comes to mind is the following.
code :


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Generic type unification: multiple parameters (T,T) vs. multiple parameter lists (T)(T)?

Generic type unification: multiple parameters (T,T) vs. multiple parameter lists (T)(T)?


By : Charles Sipe
Date : March 29 2020, 07:55 AM
it should still fix some issue I think that in the first case it is upcasting (downcasting?) both arguments such that T:Any. In the second, it is currying for Int, and then failing on the String.
This seems to bear me out:
code :
scala> y(1)_
res1: Int => Boolean = <function1>
Haskell - type wrappers unification

Haskell - type wrappers unification


By : Kehang Han
Date : March 29 2020, 07:55 AM
will help you I think the problems boils down to this: The list can have elements of the same type only; which means that either you have to 'coalesce' it into a single type in your f, or you cannot rely on haskells type checks. E.g. the following code would work for you, but the type check is runtime:
code :
{-# LANGUAGE GADTs #-}

import Control.Arrow (second)

data Item where
    A :: String -> Item
    B :: Int -> Item

unpack (A s) = s
unpack (B i) = show i

myf a@(A {}) b@(B {}) c@(B {}) = 
    let g = [("a", a), ("b", b), ("c", c)]
    in map (second unpack) g
myf _ _ _ = error "Bad types"

main = do
    putStrLn $ show $ myf (A "test") (B 13) (B 14)
    putStrLn $ show $ myf (A "test") (B 13) (A "xxx")
{-# LANGUAGE ExistentialQuantification #-}
import Control.Arrow (second)

class Value a where
    unpack :: a -> String
newtype A = A String
newtype B = B Int

instance Value A where
    unpack (A a) = a

instance Value B where
    unpack (B b) = show b

data Item = forall b. Value b => Item b
a =: b = (a, Item b)

myf :: A -> B -> B -> [(String, String)]
myf a b c = 
    let g = ["a" =: a, "b" =: b, "c" =: c]
    in map (second (\(Item x) -> unpack x)) g

main = do
    putStrLn $ show $ myf (A "test") (B 13) (B 14)
How to allow unification of a type variable with different types?

How to allow unification of a type variable with different types?


By : Sky kun
Date : March 29 2020, 07:55 AM
I wish this helpful for you I have a function with a following type signature
code :
Try {-# LANGUAGE NoMonomorphismRestriction #-}
Type unification with multi-parameter type classes

Type unification with multi-parameter type classes


By : Sean Kovacs
Date : March 29 2020, 07:55 AM
help you fix your problem I can tell you why the first one doesn't work.
Coerce could potentially be defined for any possible pair of types. coerce 0 :: Int is parsed as (coerce 0) :: Int. So you've fixed the b in coerce :: a -> b with the type annotation, but not the the a.
Unification and implicit cast of the type parameter

Unification and implicit cast of the type parameter


By : Abdul Quadir
Date : March 29 2020, 07:55 AM
this one helps. There are three ways to interpret and answer your question:
1. foo(v:B):
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