Choice

Choosing between two alternatives depending on a condition is written in Elan as:


\begin{elan} IF condition THEN part for condition true ELSE part for condition false FI \end{elan}

If the condition evaluates to true, then the paragraph between THEN and ELSE (the ``then-part'') is executed, and the rest up to the FI skipped. In the contrary case, the then-part is skipped, and the paragraph between ELSE and FI is executed (the ``else-part''). The keyword FI may also be spelled as ENDIF.

This primary form of choice has two variations for common needs. If there is nothing to do in the else-part, then the choice can be simplified by leaving out the else-part:


\begin{elan} IF it looks like rain THEN take the umbrella with you FI \end{elan}

In case the weather is fine you do nothing (ELSE do nothing was omitted). For decision cascades like


\begin{elan} IF condition 1 THEN action 1 ELSE IF condition 2 THEN action 2 ELSE IF ... FI FI FI \end{elan}

Elan offers another variant of the choice construction:


\begin{elan} IF condition 1 THEN action 1 ELIF condition 2 THEN action 2 ELIF ... ELSE action for all conditions above failing FI \end{elan}

Also in this case, an empty else-part may be omitted.