Hi Yotam,
Template Haskell expression quotes must start with either `[|` or
`[e|`, but instead these start with `[e |` - note the space. They are
list comprehensions which filter to just the elements of `es` that
match the `(dL -> L _ (Present _ e))`. Also, the `dL -> ...` portion
is a view pattern that is equivalent to `id`, since since the
arguments are already wrapped in `L`.
For something like `runQ [| Foo b <- Foo 1 |]` to work, there'd need
to be a quotation for `Stmt`, but there are only quotations for `Exp`
/ `[Dec]` / `Type` / `Pat`.
I hope that's helpful!
-Michael
On Sat, Dec 8, 2018 at 3:30 AM Yotam Ohad
Hi, In the function DsMeta.repE there is a format being repeated: For example in:
repE e@(ExplicitTuple _ es boxed) | not (all tupArgPresent es) = notHandled "Tuple sections" (ppr e) | isBoxed boxed = do { xs <- repLEs [e | (dL->L _ (Present _ e)) <- es] ; repTup xs } | otherwise = do { xs <- repLEs [e | (dL->L _ (Present _ e)) <- es] ; repUnboxedTup xs }
There is `(dL->L _ (Present _ e)) <- es`. I don't understand how this type checks correctly. If I'll try to do
data Foo a = Foo a runQ [| Foo b <- Foo 1 |]
in ghciI get an error. What is the difference?
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