887 Recall that we want to lex a little programming language,

   887 Recall that we want to lex a little programming language, called the

   888 called the \emph{While}-language. A simple program in this

   888 \emph{While}-language. A simple program in this language is shown in

   889 language is shown in Figure~\ref{while}. The main keywords in

   889 Figure~\ref{while}. The main keywords in this language are

   890 this language are \pcode{while}, \pcode{if}, \pcode{then} and

   890 \pcode{while}, \pcode{if}, \pcode{then} and

   891 \pcode{else}. As usual we have syntactic categories for

   891 \pcode{else}.\footnote{Contrast this with the COBOL programming

   892 identifiers, operators, numbers and so on. For this we would

   892   language, which was developed around 1960 and thought to be dead for

   893 need to design the corresponding regular expressions to

   893   many decades---even your friendly lecturer is not old enough to have

   894 recognise these syntactic categories. I let you do this design

   894   been taught this language. Anyway, this language had over 600

   895 task. Having these regular expressions at our disposal, we can

   895   keywords (or what they called \emph{reserved words}). Interestingly

   896   though this language is still used in 2020: during the height of

   897   Corona crisis the State of New Jewrsey in the US was looking for

   898   COBOL programers who could fix the state's national insurance

   899   webpage. You were probably paid in gold and diamonds, if you were

   900   able to program in COBOL. If you fixed their webpage, surely you

   901   were allowed to marry the governer's son/daughter. } As usual we

   902 have syntactic categories for identifiers, operators, numbers and so

   903 on. For this we would need to design the corresponding regular

   904 expressions to recognise these syntactic categories. I let you do this

   905 design task. Having these regular expressions at our disposal, we can