Pattern Clauses

There are now three types of pattern clauses:

1. Assign pattern clauses (discussed in Basic SPA requirements)
2. While pattern clauses
3. If pattern clauses

In while and if patterns, we are looking at matching control variables. A control variable is a variable that is used in the conditional expression of a container statement.

While pattern and if pattern has 2 arguments and 3 arguments within the parenthesis respectively.

• Similar to assign pattern, the first argument within the parenthesis can only be:
  • variable synonym
  • wildcard _
  • variable name in quotes
• The second (and third) argument can only be a wildcard _.

Example:

Code 13

procedure p {
1.  if (1 == 2) then {
2.      while (3 == 4) {
3.          x = 1; } }
    else {
4.      if (x == 1) then {
5.          while (y == x) {
6.              z = 2; } }
        else {
7.          y = 3; } } } }

The following queries will yield these answers:

if ifs; while w;

• Select ifs pattern ifs(_,_,_) will return 4, as only stmt 4 is a if statement uses variable(s) in conditional expression
• Select w pattern w(_,_) will return 5 as only stmt 5 is a while statement uses variable(s) in conditional expression
• Select <ifs, v> pattern ifs(v,_,_) will return 4 x
• Select <w, v> pattern w(v,_) will return 5 x, 5 y