[#15] Add lenses for config-related types #17
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Problem: It's quite unconvenient to access config-related records' fields by hand, especially when it comes to nested ones. Solution: Implement simple `makeLenses` function to derive lenses for an arbitrary product type and add common lenses operators & types.
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@Martoon-00 |
Hmhm, given that you already have field type available within I also don't see obvious troubles we could get, but would like to follow the practices here unless there is a major reason not to do so. |
| l ?= b = modify (l ?~ b) | ||
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| (&~) :: s -> State s a -> s | ||
| s &~ l = execState l s |
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Ah, I think actually we don't need operators and other helpers, especially if this is a functionality that we will have to cover with tests (we would really have to). We may need Lens type, but only if it will be used to define our new lenses.
The point is not to provide a simple replacement for lens library, but rather to be compatible with lens without depending on it. So that the user who wants to use our new lenses to configure the options, could use them along with lens package; and the user who does not want to use lens could go completely without them.
| body = [| (\x -> $(record a fieldName [|x|])) | ||
| `fmap` $(appE (varE f) (appE (varE fieldName) (varE a))) | ||
| |] | ||
| record rec fld val = val >>= \v -> recUpdE (varE rec) [return (fld, v)] |
| defLine = clause pats (normalB body) [] | ||
| pats = [varP f, varP a] | ||
| body = [| (\x -> $(record a fieldName [|x|])) | ||
| `fmap` $(appE (varE f) (appE (varE fieldName) (varE a))) |
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Minor suggestion: if you use appE in infix form here too, that should be slightly more readable.
| TyConI (DataD _ _ _ _ [RecC _ fs] _) -> fs | ||
| TyConI (NewtypeD _ _ _ _ (RecC _ fs) _) -> fs | ||
| TyConI (DataD _ _ _ _ [_] _) -> | ||
| error $ "Can't derive lenses without record selectors: " ++ datatypeStr |
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Better use fail, error is for internal errors and will be reported respectively.
This adds common
Lenstypes & operators and implements simplemakeLensestemplate-haskell function to derive lenses for config-related types.The tutorial's yet to be updated.
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Resolves #15
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