maybe-scala-compiler-bug.scala

// I really do not like using the syntax that removes points

scala> List("one","two") foldLeft ("") (_+_)
<console>:6: error: missing parameter type for expanded function ((x$1, x$2) => x$1.$plus(x$2))
       List("one","two") foldLeft ("") (_+_)
                                        ^
// Int ???

scala> List("one","two") foldLeft ("") ((_+_):(String,String) => String)
<console>:6: error: type mismatch;
 found   : (String, String) => String
 required: Int
       List("one","two") foldLeft ("") ((_+_):(String,String) => String)
                                             ^


scala> List("one","two").foldLeft ("") (_+_)
res2: java.lang.String = onetwo

I love ML currying, but this is not it and often it gets unpredictable to me. I guess there is a problem of precedence before the type inferencer kicks in. It is very confusing since it is hard to grasp even forgetting about this very case. I don't seem to be getting the mental model and that's why I tent to use it very rarely and only in places where it is clear and obvious.