Just Foo { foo = 42 } is valid Haskell syntax. I actually take advantage of this in patterns sometimes, although it can definitely be a bit confusing. (And in expressions, I 100% would have extra parentheses, otherwise it's too visually confusing.)
Dear Cafe,
I could use a parser that is equivalent
to the one produced by "deriving Read" but ...
A) faster, and using less space (Data.Text(.Lazy) instead of String)
B) streaming (parse a long list literal "[0,1,2, ... ]" in constant space,
produce the first cons of the result right after reading "[0")
C) with some minimal error reporting (e.g., some prefix of not-consumed input)
perhaps attoparsec with some form of early-commited choice?
I do have something (only for A) at
https://codeberg.org/jwaldmann/text-read (attoparsec on lazy text)
and it seems twice as fast as "deriving Read" in my tests.
NB: I was quite shocked to see that "deriving Read" accepts
"Just Foo { foo = 42 }" (no parentheses around the record literal)
(while "deriving Show" produces them).
- J.W.
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