add | between BoolType and VoidType

book.tex

@@ -15775,7 +15775,7 @@ and augments programs to include a list of function definitions.
 
 \newcommand{\LfunMonadASTPython}{
   \begin{array}{lcl}
-    \Type &::=& \key{IntType()} \MID \key{BoolType()} \key{VoidType()}
+    \Type &::=& \key{IntType()} \MID \key{BoolType()} \MID \key{VoidType()}
         \MID \key{TupleType}\LS\Type^+\RS\\
         &\MID& \key{FunctionType}\LP \Type^{*} \key{, } \Type \RP \\
     \Exp &::=& \FUNREF{\itm{label}}{\Int} \MID \CALL{\Atm}{\Atm^{*}}\\