Corrections for Task documentation concerning use of ==

[halfzebra]

Corrections for Task module documentation.

The relevant issue #502 was:

Documentation suggests that == works on tasks, but it doesn't

For example, the documentation of Task.map2 (http://package.elm-lang.org/packages/elm-lang/core/3.0.0/Task#map2) contains this line:

map2 (+) (succeed 9) (succeed 3) == succeed 12

However, issuing that exact line in a program will actually evaluate to False. Very confusing, for example to @paparga here.

Maybe the documentation shouldn't be using == on tasks, and indeed maybe it should explicitly mention that == is wonky on tasks, as the documentation already says elsewhere about Dict etc.

(Note: For Dict etc., equality could potentially be made unwonky, but for tasks not.)

I have replaced all equality operators == with comment -- to standardize the style of the docs(before it had both in different places)

Also I have added a note, that == shoudn't be used with Tasks.

[jvoigtlaender]

An example of where already the current docs use -- instead of == is the documentation of onError, which has these lines:

fail "file not found" `onError` (\msg -> succeed 42) -- succeed 42
succeed 9 `onError` (\msg -> succeed 42)             -- succeed 9

This PR fixes the other examples on that doc page to be given in the same style (and thus avoids confusing uses of == on tasks).

[jvoigtlaender]

An example of where already the current docs use -- instead of == is the documentation of onError, which has these lines:

fail "file not found" `onError` (\msg -> succeed 42) -- succeed 42
succeed 9 `onError` (\msg -> succeed 42)             -- succeed 9

This PR fixes the other examples on that doc page to be given in the same style (and thus avoids confusing uses of == on tasks).

[evancz]

Thanks, makes sense!

[evancz]

Thanks, makes sense!