If
The if statement allows for comparisons and tests for the purpose of making choices of things to do. One or more comparisons, separated by boolean operators, are made, and if all of the comparisons are successful, statement1 is executed. If any comparison in the if statement fails, the optional else clause is invoked, and statement2 is executed, otherwise execution continues with the statement following the if statement.
Statement1 may appear immediately after the if statement, or may appear on the next line. Statement2, if present, may appear immediately after the else clause, or on the next line. The else may optionally be followed by a colon (:). If the code to be executed in statement1 and/or in statement2 exceeds one line, it must be placed in a block consisting of an open brace { followed by the code to be executed and closed with a close brace }.
The types of comparisons which may be made are as follows:
| type | sample |
|---|---|
| case 1: | <value1> |
| case 2: | <value1> operator <value2> |
| case 3: | not <value1> |
- In a case 1 comparison, value1 is compared to true, which is the boolean value true, or any number other than zero. If the result evaluates to true, the comparison is successful.
- In a case 2 comparison, value1 is compared to value2 according to the supplied operator, and both values must be equivalent, either they are both numbers, both boolean values, or both strings. The possible comparisons are as follows
| operator | comparison | meaning |
|---|---|---|
| < (less than) | value1 < value2 |
if value1 is less than value2, the comparison is successful |
| > (greater than) | value1 > value2 |
if value1 is greater than value2, the comparison is successful |
| = (equal) | value1 = value2 |
if value1 is equal to value2, the comparison is successful |
| ~= (not equal) | value1 ~= value2 |
if value1 is not equal to value2, the comparison is successful |
| <= (less than or equal) | value1 <= value2 |
if value1 is less than or equal to value2, the comparison is successful |
| >= (greater than or equal) | value1 >= value2 |
if value1 is greater than or equal to value2, the comparison is successful |
| is | object1 is attribute2 |
if the specified attribute2 is set in object1, the comparison is successful |
| is not | object1 is not attribute2 |
if the specified attribute2 is not set in object1, the comparison is successful |
- In a case 3 comparison, the operator is not and the result is tested to determine if it is false, and if the result is false, the comparison is successful
The boolean operators that separate each comparison are as follows:
| boolean operator | meaning |
|---|---|
| comparison1 and comparison2 | if both comparisons are true, the result is successful. |
| comparison1 or comparison2 | if either comparison is true, the result is successful. |
| not comparison2 | if comparison2 is not true, the result is successful. |
If there are questions over how the comparisons are to be made, they may be isolated within parentheses. For example
if self is open and self is locked or self is switchable
Would test to see if the item is open, and it is locked, then test if it is switchable. Only if all three tests succeed will the test succeed. However, if the intended test was open and locked, or if it is switchable, then parentheses are required, like this:
if (self is open and self is locked) or (self is switchable)
In this case, if it passes the first two tests, or the second test, it succeeds.