Scala contiguous match

Question

pathTokens match {
 case List("post") => ("post", "index")
 case List("search") => ("search", "index")
 case List() => ("home", "index")
} match {
 case (controller, action) => loadController(http, controller, action)
 case _ => null
}

I wanted contiguous match. but got compile error. :(

(pathTokens match {
 case List("post") => ("post", "index")
 case List("search") => ("search", "index")
 case List() => ("home", "index")
}) match {
 case (controller, action) => loadController(http, controller, action)
 case _ => null
}

When I wrapped first match with parenparenthesis, it worked ok. Why I need parenthesis here ?

Answer 1

Unfortunately, that's how the Scala syntax is defined. Please have a look at the specification:
http://www.scala-lang.org/docu/files/ScalaReference.pdf

There you will find the following definition (p. 153, shortened for clarity):

Expr1 ::= PostfixExpr 'match' '{' CaseClauses '}'

If you dig into PostfixExpr you will eventually find SimpleExpr1 which contains the following definition:

SimpleExpr1 ::= '(' [Exprs [',']] ')'
Exprs ::= Expr {',' Expr}

That means that SimpleExpr1 (and thus PostfixExpr) can only contain other expressions (like 'x match y') when they are wrapped in parentheses.

Answer 2

Not what you want, but you can do stuff like this:

val f1 = (_: List[String]) match {
 case List("post") => ("post", "index")
 case List("search") => ("search", "index")
 case List() => ("home", "index")
}

val f2 = (_: (String, String)) match {
 case (controller, action) => loadController(http, controller, action)
}

(f1 andThen f2)(pathTokens)