Sequence

The sequential execution of the steps of an algorithm is denoted by placing a semicolon between them.


\begin{elan}
read the current page ;
turn page over ;
read the current page
\end{elan}

These are the names of three abstract algorithms to be executed one after the other. The semicolon is a separator between them (not a terminator), and can be read as ``and then''.

We call such a sequence a paragraph, and its constituents units. The example paragraph above contains 3 such units and its execution consists of the execution, in that order, of the three units. In this way the effect of the paragraph is the composition of the effects of its units. The value of a paragraph (if any) is the value of its last unit.