[Haskell-cafe] Question: Do block precedence

[Jonne Ransijn]

Possible future suggestion: Add a `InlineStatements` language pragma which
puts implicit parenthesis around `if-then-else`, `case-of` and `do` blocks,

See: http://pastebin.com/T7L6GyBu (Permanent pastebin)
for a example program.

On Mon, Feb 29, 2016 at 1:22 AM, Thomas Tuegel <ttuegel at gmail.com> wrote:

> On Sun, Feb 28, 2016 at 5:20 PM, Jonne Ransijn <yoyoyonny at gmail.com>
> wrote:
> > Dear Haskell-Cafe mailing list people (?)
> > I've been writing parenthesis around do blocks since forever now, but I
> > don't get why they are necessary. I can't seem to come up with a program
> > where they are necessary. Am I missing something or are parenthesis
> around
> > do blocks nececairy for no reason? Since parsing 'do' blocks as if they
> have
> > parenthesis around them doesn't seem to break any code, why not do so?
> >
> >     when (doBlocksNeedParenthesis) do putStrLn "This code is invalid."
> >
> >     when (doBlocksNeedParenthesis) $ do putStrLn "This code is valid."
> >
> >     when (doBlocksHaveInvisibleParenthesis) do putStrLn "These are equal
> v"
> >
> >     when (doBlocksHaveInvisibleParenthesis) (do putStrLn "These are equal
> > ^")
>
> This syntax can be ambiguous; consider:
>
> > (flip when) do putStrLn "Where do the parentheses go?" True
>
> I admit this is contrived; we could choose to put parentheses around a
> do-block only if it is the terminal argument. There is a case that is
> completely unambiguous:
>
> > (flip when) do { putStrLn "Braces might as well be parentheses." } True
>
> Certainly, I don't see why this shouldn't parse.
>
> Regards,
> Tom
>
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