-If you would like GHC to check that every top-level value has a type
-signature, use the \tr{-fsignatures-required}
-option.\index{-fsignatures-required option}
+GHC has a selection of options that select which types of non-fatal
+error messages, otherwise known as warnings, can be generated during
+compilation. By default, you get a standard set of warnings which are
+generally likely to indicate bugs in your program. These are:
+\tr{-fwarn-overlpapping-patterns} and \tr{-fwarn-missing-methods}.
+The following flags are simple ways to select standard ``packages'' of
+warnings:
+
+\begin{description}
+
+\item[\tr{-Wnot}:]
+\index{-Wnot option}
+
+Turns off all warnings, including the standard ones.
+
+\item[\tr{-W}:]
+\index{-W option}
+
+Provides the standard warnings plus \tr{-fwarn-incomplete-patterns}
+and \tr{-fwarn-unused-names}.
+
+\item[\tr{-Wall}:]
+\index{-Wall option}
+
+Turns on all warning options.
+
+\end{description}
+
+The full set of warning options is described below. To turn off any
+warning, simply give the corresponding \tr{-fno-warn-...} option on
+the command line.
+
+\begin{description}