Pattern matching

Pattern matching is a generalization of C language or Java's switch statement. In C language and Java, the switch statement only allows you to choose from many statements based on an integer (including char) or an enum value. While in Opa, pattern matching is more powerful than that. The more general syntax for pattern matching is:

match(<expr>){
case <case_1>: <expression_1>
case <case_2>: <expression_2>
case <case_n>: < expression_n>
}

When a pattern is executed, <expr> is evaluated to a value, which is then matched against each pattern in order until a case is found. You can think about it this way:

if (case_1 matched) expression_1 else {
  if (case_2 matched) expression_2 else {
    ...
         if (case_n matched) expression_n else no_matches
         ...
  }
}

The rules of pattern matching are simple and are as follows:

• Rule 1: Any value matches the pattern _

• Rule 2: Any value matches the variable pattern x, and the value...