Hi Gary,
We've had requests like this before
(Though I can't find it in http://haskell.systemsz.cs.yale.edu/hugs-bugs/)
If anyone feels like adding this, I'll be happy to add it in.
Here's how I think it can be done:
1) In an early phase of the compiler, add this line to the end
of every case analysis/ pattern match:
_ -> hugsError __FILE__ __LINE__
where hugsError is a new builtin function and __FILE__ and __LINE__ are
replaced by appropriate strings and ints.
2) After expanding each pattern match, try to eliminate redundant patterns.
For example, print a warning if you find:
case e of
[] -> e1
[] -> e2
or
case e of
[] -> e1
(:) x xs -> e2
_ -> e3
Suppress the warning if e3 is a call to hugsError
Remember to watch for these special cases:
case e of
x | True -> e1 -- always executes
x | otherwise -> e2 -- always executes
...
3) Print a warning message if and calls to hugsError remain at the end.
> This isn't a bug in Hugs; it's a request for an enhancement.
>
> It would be very nice if hugs would statically check the definitions
> in a module to see if all patterns for a type are covered. For example, if
> the user wrote a function
>
> > sum_all :: [Int] -> Int
> > sum_all (x:xs) = x + sum_all xs
>
> then hugs should warn the user that the pattern [] is not covered
> by the definition. This warning might be toggled by a command line
> switch if annoying.
>
> SML has this feature, at least in the implementations I've used (SML/NJ),
> and it's very helpful for students.
>
> Gary Leavens
> 229 Atanasoff Hall, Department of Computer Science
> Iowa State Univ., Ames, Iowa 50011-1040 USA
> [EMAIL PROTECTED] phone: +1 515 294-1580 fax: +1 515 294-0258
> URL: http://www.cs.iastate.edu/~leavens/homepage.html
>
