Part of the While grammar for Statements and Arithmetic Expressions:
\[\begin{array}{rcl}
S &\longrightarrow& V \leftarrow A \mid \cdots{}\\
A &\longrightarrow& V \mid N \mid A + A \mid \cdots{}\\[6mm]
L &\longrightarrow& a \mid b \mid \cdots{} \mid z \\
U &\longrightarrow& A \mid B \mid \cdots{} \mid Z \mid '\\
M &\longrightarrow& L\ M \mid U\ M \mid \epsilon\\
V &\longrightarrow& L\ M\\
D &\longrightarrow& 0 \mid 1 \mid \cdots{} \mid 9\\
E &\longrightarrow& D\ E \mid \epsilon\\
N &\longrightarrow& D\ E
\end{array}\]