modifyConfig :: (Config -> a) -> (a -> a) -> Config -> Config modifyConfig fr fv a = a { fr = fv (fr a)
I like this Idea. The only problem I see is this: if I'm trying to write code that is very generic and abstract, how does the compiler know if the update
a { fr = 5 }
is targeting a field fr of the record a, or a variable fr, which is in scope and "points to" a first-class field. The difference depends on the record in question, so the code would work differently depending on the context. I would think it would have to be something like
a { :fr = 5 }
or something else syntactically distinct from current record update syntax. With this and a few more conveniences on record syntax, lenses could go away. For example, I'd love to see a "lambda update" syntax. For example instead of:
setName n r = r {name = n}
we'd write
setName n = \{name = n}
I'd also like to see an "Update field by" syntax. Instead of
addMr r = r { name = "Mr. " ++ (name r) }
we'd write
addMr r = r { name => ("Mr. "++) }
or combining the previous 2:
addMr = \{name=>("Mr. "++)}
feels very terse and "Haskelly" to me. Regards, --J Arthur