bug608.scala

JAVA 语言的函数式编程扩展

trait CrashDueToTypeError {
	def id[a](x :a) :a = x

	trait Bifunctor {
		type a; //	 content 
		type s <: Bifunctor

		// uncomment        this-vvvvvvvvvvvvvvvvvvvvvvvvvvvv, and it compiles 
		def bimap[c](f :a=>c) :s{/*type s=Bifunctor.this.s;*/type a=c; }
	}

	def hylo[hs <: Bifunctor,ha,hb,hc]
	    (f :hb=>hs{type s=hs; type a=ha}, 
	     g :hs{type s=hs; type a=ha}=>hc)(x :hb) 
	     :hc 
	     = g(f(x).bimap(id))
}