+-- | @installHandler int handler iset@ calls @sigaction@ to install an
+-- interrupt handler for signal @int@. If @handler@ is @Default@,
+-- @SIG_DFL@ is installed; if @handler@ is @Ignore@, @SIG_IGN@ is
+-- installed; if @handler@ is @Catch action@, a handler is installed
+-- which will invoke @action@ in a new thread when (or shortly after) the
+-- signal is received.
+-- If @iset@ is @Just s@, then the @sa_mask@ of the @sigaction@ structure
+-- is set to @s@; otherwise it is cleared. The previously installed
+-- signal handler for @int@ is returned