Proposal: ArgumentDo

Carter Schonwald carter.schonwald at
Thu Jul 7 17:15:55 UTC 2016

agreed -1,
ambiguity is bad for humans, not just parsers.

perhaps most damningly,

> f do{ x } do { y }

is just reallly really weird/confusing to me, and as the proposal
itself says at the end as the cons:

   - It's harder to read than the alternative.
>    - Creating a language extension to get rid of a single character is overkill and unnecessary.
>    - You can already get rid of the $ by just adding parentheses.

which kinda kills any benefit in my mind. thats a HUGE complexity vs
alternative ratio. I'm all in favor of doing engineering work to
*improve* our parser error messages and suggestions, but not stuff
that complicates parsing for humans  as well as machines

On Wed, Jul 6, 2016 at 9:50 PM, Evan Laforge <qdunkan at> wrote:

> On Wed, Jul 6, 2016 at 10:39 AM, Bardur Arantsson <spam at>
> wrote:
> > On 07/04/2016 12:31 PM, Akio Takano wrote:
> >> Hi glasgow-haskell-users,
> >>
> >> I have written a wiki page about a proposed extension called
> >> ArgumentDo. It's a small syntactic extension that allows "do"
> >> expressions, lambdas and a few other kinds of expressions to be used
> >> as function arguments, without parentheses.
> >>
> >>
> >>
> >> Any feedback is appreciated. In particular, since the idea has
> >> received mixed support (see the "Discussion" section on the wiki
> >> page), I'd like to make sure that there is enough support for this
> >> feature to justify an implementation in GHC.
> >>
> >
> > -1
> >
> > Reasons have already been given in previous threads on this. However,
> > I'd point especially to the fact that people don't *agree* that this is
> > more readable as a very strong point against -- regardless of whether
> > any one individual thinks it's more readable or not. The point is the
> > there seems to be a lot of disagreement -- that indicates to me that
> > this cannot by definition be a "clear win"[1]. Disclosure: I personally
> > find it less readable because of the implicitness. Implicitness which
> > has a non-trivial probability of affecting semantics is bad in my book.
> > Frankly, if it came to it, I'd rather just remove $ and deal with the
> > parentheses.
> I'm -1 because I think there are already too many styles.  So I don't
> agree with the general sentiment that the parser should accept lots of
> stuff and to rely on style guides to specify something, because in
> practice everyone has their own style guide.
> I trained myself to see juxtaposition as highest precedence (which
> newcomers still struggle over) and it's confusing to see juxtaposition
> that has higher precedence because one of them is a keyword.  In the
> same way I'm confused by 'f a { b = c }', but it's too late to change
> that one.  I suppose this is already on the wiki page in the "cons"
> section.
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