some slight updates in ImpException.hs

check out the behaviour of exceptions

start hugs

load ImpException.hs

:l ImpException.hs
Reading file "ImpException.hs":
                   
Hugs session for:
/usr/share/hugs98/lib/Prelude.hs
ImpException.hs
Main> rundisplay prog7 "x"
N 3
Main> rundisplay prog2 "x"
N 2


Consider

prog2 :: Cmd
prog2 = Handle "error" (Assign "x" (Val (N 2))) 
                       (Seq (Assign "x" (Val (N 3))) (Raise "error"))
-- (handle "error" = x:=2
--  in x:=3; raise "error")

prog7 :: Cmd
prog7 = Handle "error" (Assign "x" (Val (N 2))) 
                       (Seq (Raise "error") (Assign "x" (Val (N 3))))
-- (handle "error" = x:=2
--  in raise "error"; x:=3)

After we raise the "error" exception (i.e. we execute the corresponding
handler routine), we continue with the next statement. Here, x:=3