doc(servant-foreign): Document module
I spend some considerable time reverse engineering the module, so I thought I’d write the documentation I would have liked to see. The strategy here is that a user not necessarily has insight into how servant works internally, or even how to write complex servant routes, they just want to generate a list of endpoints and convert the `Req` type into e.g. generated code in $language. Thus, they need to know the semantics of all fields of Req, how they interact and how they relate to a plain http route. I made sure every `f` is replaced with `ftype`, so we have one conventional way of referring to the foreign type argument everywhere. Some enums are not set at all, they are marked as such. `_reqBodyContentType` introduces a major restriction of the module, so that is mentioned in the documentation for now, until the time it will be fixed. A few TODO’s describe places where types don’t make sense but would introduce API-breaking changes, so these should probably be simplified, but bundled in one go.
This commit is contained in:
Philip Patsch
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07f7954cc6
commit
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2 changed files with 133 additions and 39 deletions
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@ -3,28 +3,30 @@
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--
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-- See documentation of 'HasForeignType' for a simple example. 'listFromAPI' returns a list of all your endpoints and their foreign types, given a mapping from Haskell types to foreign types (conventionally called `ftypes` below).
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module Servant.Foreign
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( listFromAPI
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(
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-- * Main API
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listFromAPI
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, Req(..)
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, defReq
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, HasForeignType(..)
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, GenerateList(..)
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, HasForeign(..)
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, NoTypes
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, ArgType(..)
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, HeaderArg(..)
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, QueryArg(..)
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, ReqBodyContentType(..)
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-- * Subtypes of 'Req'
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, Url(..)
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, Path
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, Segment(..)
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, SegmentType(..)
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, isCapture
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, captureArg
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, SegmentType(..)
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, Url(..)
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-- * aliases
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, Path
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, QueryArg(..)
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, ArgType(..)
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, HeaderArg(..)
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, Arg(..)
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, FunctionName(..)
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, ReqBodyContentType(..)
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, PathSegment(..)
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-- * lenses
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-- * Lenses
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, argName
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, argType
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, argPath
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@ -40,7 +42,7 @@ module Servant.Foreign
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, queryArgName
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, queryArgType
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, headerArg
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-- * prisms
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-- * Prisms
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, _PathSegment
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, _HeaderArg
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, _ReplaceHeaderArg
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@ -49,7 +51,7 @@ module Servant.Foreign
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, _Normal
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, _Flag
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, _List
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-- * re-exports
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-- * Re-exports
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, module Servant.API
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, module Servant.Foreign.Inflections
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) where
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@ -46,45 +46,67 @@ newtype FunctionName = FunctionName { unFunctionName :: [Text] }
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makePrisms ''FunctionName
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-- | See documentation of 'Arg'
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newtype PathSegment = PathSegment { unPathSegment :: Text }
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deriving (Data, Show, Eq, IsString, Semigroup, Monoid, Typeable)
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makePrisms ''PathSegment
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data Arg f = Arg
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-- | Maps a name to the foreign type that belongs to the annotated value.
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--
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-- Used for header args, query args, and capture args.
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data Arg ftype = Arg
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{ _argName :: PathSegment
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, _argType :: f }
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-- ^ The name to be captured.
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--
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-- Only for capture args it really denotes a path segment.
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, _argType :: ftype
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-- ^ Foreign type the associated value will have
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}
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deriving (Data, Eq, Show, Typeable)
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makeLenses ''Arg
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argPath :: Getter (Arg f) Text
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argPath :: Getter (Arg ftype) Text
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argPath = argName . _PathSegment
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data SegmentType f
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data SegmentType ftype
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= Static PathSegment
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-- ^ a static path segment. like "/foo"
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| Cap (Arg f)
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-- ^ a capture. like "/:userid"
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-- ^ Static path segment.
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--
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-- @"foo\/bar\/baz"@
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--
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-- contains the static segments @"foo"@, @"bar"@ and @"baz"@.
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| Cap (Arg ftype)
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-- ^ A capture.
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--
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-- @"user\/{userid}\/name"@
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--
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-- would capture the arg @userid@ with type @ftype@.
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deriving (Data, Eq, Show, Typeable)
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makePrisms ''SegmentType
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newtype Segment f = Segment { unSegment :: SegmentType f }
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-- | A part of the Url’s path.
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newtype Segment ftype = Segment { unSegment :: SegmentType ftype }
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deriving (Data, Eq, Show, Typeable)
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makePrisms ''Segment
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isCapture :: Segment f -> Bool
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-- | Whether a segment is a 'Cap'.
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isCapture :: Segment ftype -> Bool
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isCapture (Segment (Cap _)) = True
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isCapture _ = False
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captureArg :: Segment f -> Arg f
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-- | Crashing Arg extraction from segment, TODO: remove
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captureArg :: Segment ftype -> Arg ftype
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captureArg (Segment (Cap s)) = s
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captureArg _ = error "captureArg called on non capture"
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type Path f = [Segment f]
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-- TODO: remove, unnecessary indirection
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type Path ftype = [Segment ftype]
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-- | Type of a 'QueryArg'.
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data ArgType
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= Normal
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| Flag
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@ -93,18 +115,41 @@ data ArgType
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makePrisms ''ArgType
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data QueryArg f = QueryArg
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{ _queryArgName :: Arg f
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-- | Url Query argument.
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--
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-- Urls can contain query arguments, which is a list of key-value pairs.
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-- In a typical url, query arguments look like this:
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--
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-- @?foo=bar&alist[]=el1&alist[]=el2&aflag@
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--
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-- Each pair can be
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--
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-- * @?foo=bar@: a plain key-val pair, either optional or required ('QueryParam')
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-- * @?aflag@: a flag (no value, implicitly Bool with default `false` if it’s missing) ('QueryFlag')
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-- * @?alist[]=el1&alist[]=el2@: list of values ('QueryParams')
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--
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-- @_queryArgType@ will be set accordingly.
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--
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-- For the plain key-val pairs ('QueryParam'), @_queryArgName@’s @ftype@ will be wrapped in a @Maybe@ if the argument is optional.
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data QueryArg ftype = QueryArg
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{ _queryArgName :: Arg ftype
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-- ^ Name and foreign type of the argument. Will be wrapped in `Maybe` if the query is optional and in a `[]` if the query is a list
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, _queryArgType :: ArgType
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-- ^ one of normal/plain, list or flag
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}
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deriving (Data, Eq, Show, Typeable)
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makeLenses ''QueryArg
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data HeaderArg f = HeaderArg
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{ _headerArg :: Arg f }
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data HeaderArg ftype =
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-- | The name of the header and the foreign type of its value.
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HeaderArg
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{ _headerArg :: Arg ftype }
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-- | Unused, will never be set.
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--
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-- TODO: remove
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| ReplaceHeaderArg
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{ _headerArg :: Arg f
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{ _headerArg :: Arg ftype
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, _headerPattern :: Text
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}
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deriving (Data, Eq, Show, Typeable)
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@ -113,29 +158,71 @@ makeLenses ''HeaderArg
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makePrisms ''HeaderArg
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data Url f = Url
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{ _path :: Path f
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, _queryStr :: [QueryArg f]
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, _frag :: Maybe f
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-- | Full endpoint url, with all captures and parameters
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data Url ftype = Url
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{ _path :: Path ftype
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-- ^ Url path, list of either static segments or captures
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--
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-- @"foo\/{id}\/bar"@
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, _queryStr :: [QueryArg ftype]
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-- ^ List of query args
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--
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-- @"?foo=bar&a=b"@
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, _frag :: Maybe ftype
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-- ^ Url fragment.
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--
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-- Not sent to the HTTP server, so only useful for frontend matters (e.g. inter-page linking).
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--
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-- @#fragmentText@
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}
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deriving (Data, Eq, Show, Typeable)
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defUrl :: Url f
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defUrl :: Url ftype
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defUrl = Url [] [] Nothing
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makeLenses ''Url
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-- | See documentation of '_reqBodyContentType'
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data ReqBodyContentType = ReqBodyJSON | ReqBodyMultipart
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deriving (Data, Eq, Show, Read)
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data Req f = Req
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{ _reqUrl :: Url f
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-- | Full description of an endpoint in your API, generated by 'listFromAPI'. It should give you all the information needed to generate foreign language bindings.
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--
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-- Every field containing @ftype@ will use the foreign type mapping specified via 'HasForeignType' (see its docstring on how to set that up).
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--
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-- See https://docs.servant.dev/en/stable/tutorial/ApiType.html for accessible documentation of the possible content of an endpoint.
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data Req ftype = Req
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{ _reqUrl :: Url ftype
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-- ^ Full list of URL segments, including captures
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, _reqMethod :: HTTP.Method
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, _reqHeaders :: [HeaderArg f]
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, _reqBody :: Maybe f
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, _reqReturnType :: Maybe f
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-- ^ @\"GET\"@\/@\"POST\"@\/@\"PUT\"@\/…
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, _reqHeaders :: [HeaderArg ftype]
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-- ^ Headers required by this endpoint, with their type
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, _reqBody :: Maybe ftype
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-- ^ Foreign type of the expected request body ('ReqBody'), if any
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, _reqReturnType :: Maybe ftype
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-- ^ The foreign type of the response, if any
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, _reqFuncName :: FunctionName
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-- ^ The URL segments rendered in a way that they can be easily concatenated into a canonical function name
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, _reqBodyContentType :: ReqBodyContentType
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-- ^ The content type the request body is transferred as.
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--
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-- This is a severe limitation of @servant-foreign@ currently,
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-- as we only allow the content type to be `JSON`
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-- no user-defined content types. ('ReqBodyMultipart' is not
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-- actually implemented.)
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--
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-- Thus, any routes looking like this will work:
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--
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-- @"foo" :> Get '[JSON] Foo@
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--
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-- while routes like
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--
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-- @"foo" :> Get '[MyFancyContentType] Foo@
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--
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-- will fail with an error like
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--
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-- @• JSON expected in list '[MyFancyContentType]@
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}
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deriving (Data, Eq, Show, Typeable)
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@ -179,11 +266,16 @@ defReq = Req defUrl "GET" [] Nothing Nothing (FunctionName []) ReqBodyJSON
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class HasForeignType lang ftype a where
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typeFor :: Proxy lang -> Proxy ftype -> Proxy a -> ftype
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-- | The language definition without any foreign types. It can be used for dynamic languages which do not /do/ type annotations.
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data NoTypes
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instance HasForeignType NoTypes NoContent ftype where
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-- | Use if the foreign language does not have any types.
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instance HasForeignType NoTypes NoContent a where
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typeFor _ _ _ = NoContent
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-- | Implementation of the Servant framework types.
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--
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-- Relevant instances: Everything containing 'HasForeignType'.
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class HasForeign lang ftype (api :: *) where
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type Foreign ftype api :: *
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foreignFor :: Proxy lang -> Proxy ftype -> Proxy api -> Req ftype -> Foreign ftype api
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