Does Scala have guards?

Question

I started learning scala a few days ago and when learning it, I am comparing it with other functional programming languages like (Haskell, Erlang) which I had some familiarity with. Does Scala has guard sequences available?

I went through pattern matching in Scala, but is there any concept equivalent to guards with otherwise and all?

Answer 1

Yes, it uses the keyword if. From the Case Classes section of A Tour of Scala, near the bottom:

def isIdentityFun(term: Term): Boolean = term match {   case Fun(x, Var(y)) if x == y => true   case _ => false } 

(This isn't mentioned on the Pattern Matching page, maybe because the Tour is such a quick overview.)

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In Haskell, otherwise is actually just a variable bound to True. So it doesn't add any power to the concept of pattern matching. You can get it just by repeating your initial pattern without the guard:

// if this is your guarded match   case Fun(x, Var(y)) if x == y => true // and this is your 'otherwise' match   case Fun(x, Var(y)) if true => false // you could just write this:   case Fun(x, Var(y)) => false 

Answer 2

Yes, there are pattern guards. They're used like this:

def boundedInt(min:Int, max: Int): Int => Int = {   case n if n>max => max   case n if n<min => min   case n => n } 

Note that instead of an otherwise-clause, you simply specifiy the pattern without a guard.