Documention for def is misleading

[pbrisbin]

In the Haddocks for def it says,

Note: specifying it means the parser won't ever fail.

This is not correct:

> X="" stack ghci --package envparse
λ> Env.parse id $ Env.var (Env.eitherReader (\_ -> Left "oops")) "X" (Env.def ())
Available environment variables:

  X

Parsing errors:

  X has value oops: "hi" that cannot be parsed

I'm happy to PR a quick fix, but I wanted to see what the intention was. Is the note meant to read won't ever fail on a missing environment variable? I'd argue that's pretty obvious and would just remove the note entirely in that case.

[supki]

I think this line is simply outdated and refers to the pre-28bf50b behavior, when parse errors were replaced with default values. (optparse-applicative's value has the same note attached to it, although I'm not sure how it behaves in practice.)

I agree that it's not useful anymore and should be removed.