\begin{figure}

\begin{syntax}
\syntaxclass{Types:}
{\it signedness} & ::= &  "Signed" \alt "Unsigned" \\
{\it intsize} & ::= &  "I8" \alt "I16" \alt "I32" \\
{\it floatsize} & ::= &  "F32" \alt "F64" \\
\tau & ::= &  "Tint" ({\it intsize}, {\it signedness}) \\
     & \alt & "Tfloat" ({\it floatsize})  \\
     & \alt & "Tvoid" \\
     & \alt & "Tarray" (\tau, n) \\
     & \alt & "Tpointer" (\tau) \\
%     &\alt & "Tcomp_pointer" (\id) \\
     &\alt & "Tstruct" (\id,\seq {(\id,\tau)}) \\
     &\alt & "Tunion" (\id,\seq {(\id,\tau)}) \\
     & \alt & "Tfunction" (\seq \tau, \tau)
%
\syntaxclass{Expressions annotated with types:}
a & ::=  & \unannot{a}{\tau}
\syntaxclass{Unannotated expressions:}
b & ::=  & \id & variable identifier\\
  & \alt & n & integer constant\\
  & \alt & f & float constant \\
  & \alt & "sizeof"(\tau) & size of a type \\
  & \alt & \op_1 ~ a & unary arithmetic operation\\
  & \alt & a_1 ~\op_2 ~ a_2  & binary arithmetic operation\\
  & \alt & \hbox{"*"} a & dereferencing \\
  & \alt & a_1 [a_2] & array indexing \\
  & \alt & a \dot \id   & field access \\
  & \alt & \hbox{"&"} a & address of \\
  & \alt & (\tau) a & cast \\
  & \alt & a_1 \hbox{" && "} a_2 \alt a_1 \hbox{" || "} a_2
              & sequential boolean operations \\
  & \alt & a(\seq a) & function call \\
%
\op_2 & ::=  & \hbox{"+"} \alt \hbox{"-"} \alt \hbox{"*"} \alt \hbox{"/"} \alt \hbox{"%"}
               & arithmetic operators \\ 
      & \alt & \hbox{"<<"} \alt \hbox{">>"} \alt 
               \hbox{"&"} \alt \hbox{"|"} \alt \hbox{"^"}
               & bitwise operators\\
 &  \alt  & \hbox{"<"} \alt \hbox{"<="} \alt \hbox{">"} \alt \hbox{">="}
               \alt \hbox{"=="} \alt \hbox{"!="}
               & relational operators \\
\op_1 & ::= & \hbox{"-"} \alt \hbox{"~"} \alt \hbox{"!"}& unary operators
%
\end{syntax}
\caption{Abstract syntax of Clight (types and expressions).  $\seq a$ denotes 0, 1 or several
  occurrences of syntactic category $a$.  $\opt a$ denotes an optional
  occurrence of category $a$.}
\label{fig:syntax}
\end{figure}