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Two Level Description (2)

Why two levels

For a practical specification we will use:

Context-free Syntax
$\begin{program} Expression~\==~Expression~(~''--''~$\vert$~''+''~)~Term~$\vert$~... ...rt$~Factor. \\ Factor~\\ gt=~numlit~$\vert$~''(''~Expression~'')''.\end{program}$
Lexical Syntax
$\begin{program} numlit~\==~digit~\{~digit~\}. \\ digit~~\\ gt=~''0''~$\vert$~...~$\vert$~''9''.\end{program}$

But for the actual implementation we will use the first scheme.

Christoph Zenger
3/16/2000