IF, ELSE, ELSEIF - conditional execution



<IF condition1>
  ... statements if condition1 true ...
[<ELSE[ ]IF condition2>
  ... statements if condition2 true ...]
  ... statements if both are false ...]

The IF statement evaluates the given conditional expression. If the result is true (i.e. nonzero), then the statements following the <IF> tag are executed. If the result is false, those statements are skipped and control falls to the next statement after the closing </IF> tag.

An optional ELSE clause may be present, in which case the statements following the <ELSE> tag are executed instead if the result is false. If the ELSE clause is another IF statement, it can be made part of the <ELSE> tag by using <ELSEIF>. Thus, the left and right statements below are equivalent:

<IF $x eq 5>                     <IF $x eq 5>
  X is five.                       X is five.
<ELSE>                           <ELSEIF $y gt 10>
  <IF $y gt 10>                    Y is greater than 10.
    Y is greater than 10.        <ELSE>
  <ELSE>                           X is not five and Y is <= 10.
    X is not 5 and Y is <= 10.   </IF>

If many ELSEIF clauses are used on the same value, a SWITCH statement (here) may be a clearer alternative.

The condition of an IF statement can be simple or complex. A simple condition is of the form arg1 op arg2, where each arg is a variable or literal string, and op is one of the following operators:

  • eq or =: Equals

  • ne or neq: Does not equal

  • gt: Greater than

  • ge or gte: Greater than or equal to

  • lt: Less than

  • le or lte: Less than or equal to

  • nmod: Not mod; true if value1 mod value2 is 0

For example:

<IF $temp lt 32>

A SQL expression condition can be any valid Texis SQL WHERE clause. Thus, and and or may be used, or even like:

<IF $limit lt 5 and ($ans eq "correct" or $body like $query)>
  You're under the limit, and either
  have the correct answer or the text matches your query.

Variables should not be embedded inside a literal string, e.g. "this is a $test". Literal string values should always be quoted, or they may be misconstrued as non-existent SQL columns.

The results of some operators can depend on the original type of the values, e.g. comparison of integer vs. string values (see discussion under Variable Types, here).

If a variable contains more than one value in its current context (i.e. outside a LOOP), only the 0th (first) value is used. An empty (no values) variable is considered an empty string.


Copyright © Thunderstone Software     Last updated: Aug 4 2020
Copyright © 2021 Thunderstone Software LLC. All rights reserved.