Hi Henrik,
On 9 July 2016 at 09:46, Henrik Nilsson
Hi all,
On 07/09/2016 08:09 AM, C Maeder wrote:
The asymmetry that you mention is already apparent for (Haskell98) infix expressions, i.e. when "composing" lambda- or if-expression:
(if c then f else g) . \ x -> h x
Parentheses around the last argument of "." do not matter, but parentheses around the first argument make a real difference
But that has to do with how grammatical ambiguity related to in this case "if" and "lambda" are resolved by letting the constructs extend as far as possible to the right.
This the standard way of resolving that kind of ambiguity across a very wide range of programming languages and parsing tools (e.g. preferring shift over reduce in an LR parser). (And also in principle how lexical ambiguities are typically resolved, sometimes referred to as the "maximal munch rule".)
In contrast, the present proposal suggests treating different argument positions in grammatically different ways (different non-terminals). As far as I know, that is unprecedented. And in any case, it manifestly complicates the grammar (more non-terminals) and as a consequence adds another grammatical hurdle to learning the language.
Thank you for pointing this out. I have updated the proposal so that it doesn't introduce a new non-terminal. I'm not sure if it should be implemented this way in the GHC parser, but this is probably a separate question. - Akio