Is there way to match strings in scala like this:
def matcher(arg: String) : Expr = {
case left :: '*' :: right => new Binary("*", left, right)
case left :: '+' :: right => new Binary("+", left, right)
}
where left and right are have type String?
You can achieve your goal by matching on regular expressions.
trait Expr
case class Binary(op: String, leftOperand: String, rightOperand: String) extends Expr
val mulPattern = "(\\d*)\\*(\\d*)".r
val addPattern = "(\\d*)\\+(\\d*)".r
def matcher(arg: String) : Expr = {
arg match {
case mulPattern(left, right) => new Binary("*", left, right)
case addPattern(left, right) => new Binary("+", left, right)
}
}
def main(args: Array[String]): Unit = {
println(matcher("1+2")) // Binary("+", "1", "2")
println(matcher("3*4")) // Binary("*", "3", "4")
}
def binRegex(symbol: Char) = raw"""([^$symbol]+)[$symbol]([^$symbol]+)""".r
I don't think so.
You might be able to do it, if you convert the String into a List or Vector of Char and then revert the results with mkString. But I haven't be able to come up with something.
However, imo, a regular expression would be more concise and readable:
trait Expr
case class Binary(op: String, left: String, right: String) extends Expr
val Expression = """(.*?)\s*([+-\/\^\*])\s*(.*)""".r
def matcher(arg: String) : Expr = arg match {
case Expression(left, op, right) => new Binary(op, left, right)
}
val test = matcher("a + b")
val test2 = matcher("a * b")
You can also do this with extractors:
object Mult {
def unapply(x: String): Option[(String, String)] = x.split("\\*") match {
case Array(a: String, b: String) => Some(a -> b)
case _ => None
}
}
object Add {
def unapply(x: String): Option[(String, String)] = x.split("\\+") match {
case Array(a: String, b: String) => Some(a -> b)
case _ => None
}
}
def matcher(arg: String) = arg match {
case Mult(left, right) => Binary("*", left, right)
case Add(left, right) => Binary("+", left, right)
case _ => println("not matched")
}
You may also want to implement apply method for each extractor like:
def apply(l: String, r: String) = s"$l*$r"
but this is not mandatory
