[Haskell-cafe] Testing for valid data

Jason Dagit dagit at codersbase.com
Sun Mar 28 04:09:08 EDT 2010

On Sat, Mar 27, 2010 at 2:42 PM, michael rice <nowgate at yahoo.com> wrote:

> Hi Ketil,
> Good point, but I think it side-steps the question. Haskell coughs on a
> data value. Do we grep our data, finding and fixing the offender, or build
> extensive data tests into our application code?

I'm not convinced I understand your question, but I think I get part of it.
 I think approaches where you munge the input to make it fit your
expectations are almost always wrong.  They tend to lead to subtle problems
and overcomplication.  Consider HTML in the early days compared to more
recent developments in that area.  Back in the late 90s and early 2000s
browsers were being made that just magically accepted invalid HTML and
silently interpreted it in whatever ways the authors felt like.  Things
aren't perfect now, but I think it's been getting better by having the
implementations be pickier about malformed input.

As for building extensive data tests, I'm not sure what you mean here.  I
would have to see examples.  Often if you have a solid parser that throws
detailed errors on invalid input then you're good to go right?  And of
course, you don't want to let garbage into your program.  That's going to
lead to headaches.

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