Parsing/Shunting-yard algorithm: Difference between revisions
Add Scala implementation
m (→{{header|Wren}}: Minor tidy) |
(Add Scala implementation) |
||
Line 4,566:
calculate(postfix_tokens)
}</syntaxhighlight>
=={{header|Scala}}==
{{trans|Java}}
<syntaxhighlight lang="Scala">
import scala.util.control.Breaks._
object ShuntingYard {
def main(args: Array[String]): Unit = {
val infix = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3"
println(s"infix: $infix")
println(s"postfix: ${infixToPostfix(infix)}")
}
def infixToPostfix(infix: String): String = {
val ops = "-+/*^"
val sb = new StringBuilder
val s = scala.collection.mutable.Stack[Int]()
infix.split("\\s").foreach { token =>
if (token.nonEmpty) {
val c = token.head
val idx = ops.indexOf(c)
if (idx != -1) {
if (s.isEmpty) s.push(idx)
else {
breakable({
while (s.nonEmpty) {
val prec2 = s.top / 2
val prec1 = idx / 2
if (prec2 > prec1 || (prec2 == prec1 && c != '^')) sb.append(ops(s.pop)).append(' ')
else break
}
});
s.push(idx)
}
} else if (c == '(') {
s.push(-2) // -2 stands for '('
} else if (c == ')') {
// until '(' on stack, pop operators.
while (s.top != -2) sb.append(ops(s.pop)).append(' ')
s.pop()
} else {
sb.append(token).append(' ')
}
}
}
while (s.nonEmpty) sb.append(ops(s.pop)).append(' ')
sb.toString
}
}
</syntaxhighlight>
{{out}}
<pre>
infix: 3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3
postfix: 3 4 2 * 1 5 - 2 3 ^ ^ / +
</pre>
=={{header|Sidef}}==
| |||