Open Radar

 
Summary:
Trying to typecheck a simple program using currying & applicative functors is unreasonably slow.


Steps to Reproduce:
1. Compile this program (note that it does not pass typechecking):

func curry<A, B, R>(f: (A, B) -> R) -> A -> B -> R {
	return { a in { b in f(a, b) } }
}

infix operator <*> { associativity left precedence 150 }
func <*><A, B>(lhs: (A -> B)?, rhs: A?) -> B? {
	if let lhs1 = lhs {
		if let rhs1 = rhs {
			return lhs1(rhs1)
		}
	}
	return nil
}

func cons<T, U>(lhs: T, rhs: U) -> (T, U) {
	return (lhs, rhs)
}

var str1: String? = "👍"
var str2: String? = "👍"
var str3: String? = "👍"

if let f = curry(cons) <*> str1 <*> curry(cons) <*> str2 <*> str3 {
	println("\(f)")
}


Expected Results:
Responsive (interactive!) typechecking.


Actual Results:
Resonance:Desktop rob$ time ./Applicative.swift 
./Applicative.swift:25:12: error: '(T, U)' is not a subtype of 'String -> (String -> B)'
if let f = curry(cons) <*> str1 <*> curry(cons) <*> str2 <*> str3 {
           ^

real	0m29.714s
user	0m29.414s
sys	0m0.288s


Regression:
N/A


Notes:
Attached a sample.