On 10/24/2016 02:15 PM, Dan Liebgold wrote:
On Sunday, October 23, 2016 at 1:14:56 PM UTC-7, Ryan Culpepper wrote:
[...]
1. A term like `(a <- blend)` will match the first pattern and treat
`blend` as a `remap:id`. If you don't want that to happen, there are two
ways to prevent it. One is to define a syntax class like `id` that
excludes all of the reserved words like `<-` and `blend` and use that
for pattern variables like `remap`. The other is to reorder the patterns
and use cut (~!):
(pattern (source:id <- blend ~! remap:id
extras:remap-entry-extra-params))
(pattern (source:id <- remap:id extras:remap-entry-extra-params))
This one is surprising. I thought that listing 'blend' as a datum-literal would
prevent the more general 'remap:id from matching it.
It might make sense for syntax-parse to offer something like Redex's
`variable-not-otherwise-mentioned`, which would behave like you
expected. I think it would have to be a baked-in special case, but it
might be useful enough to justify that.
I ran into the same issue recently when designing an(other) S-expression
notation for SQL.
Ryan
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