Proposal: require spaces around the dot operator

Gábor Lehel illissius at
Sat Feb 11 18:16:23 CET 2012

On Sat, Feb 11, 2012 at 4:07 PM, Doug McIlroy <doug at> wrote:
> For example, this code fragment to define addition on lists
> is instantly intelligible.
> instance Num a => Num [a] where
>        (f:fs) + (g:gs) = f+g : fs+gs
> But the formula becomes merely an obscure procession of symbols when
> rewritten with the operators set off by spaces:
>        ( fs : gs ) + ( g : gs ) = f + g : fs + gs

I wouldn't require them inside parentheses, but that's a very good
point: the list constructor in patterns is an example of an operator
where basically no one ever uses spaces.

> And it becomes too long and too subtly modulated to take in at
> a glance if more spacing is added to emphasize precedence:
>        ( f : fs )  +  ( g : gs )   =   f + g   :   fs + gs

I would rather write (f + g) : (fs + gs), but point taken.

In any case, while I would in theory support spaces around all
operators, modulo counterexamples such as those presented above, I'm
not proposing it and I don't think anyone is, so it's probably best to
stick to discussing spaces around (.) (which I also support).
Apologies for taking the discussion off topic.

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