haskell: reader-monad for dependency-injection
i get the basic functionality of the reader-monad from learnyouahaskell book and i've seen some advises here to make use of it for dependency-injection.
even there are some examples here on stackoverflow, i dont know how to use it for integration-testing.
my code is:
list :: Ctx -> [String] -> IO String
list ctx args = do
d <- eitherDecode <$> Uplink.get (token ctx) (endpointActivities ctx) :: IO (Either String Activities)
case d of
Left err -> return err
Right result -> return $ unlines . filterByPrefix (parsePrefix args) . extractNames $ activities result
uplink.hs
get :: String -> String -> IO B.ByteString
get token endpoint = do
req <- parseRequest endpoint
resp <- httpLBS $ withAuth token req
return $ getResponseBody resp
how can i mock the httpLBS - call for integration-testing with the reader-monad?
EDIT: !!!!
i almost have it now with the reader-monad. the only problem left is that i dont know how i can define that httpsLBS-function in my Ctx-data-type.
httpLBS-function-signature:
httpLBS :: MonadIO m => Request -> m (Response ByteString)
my Ctx data-type-definition:
data Ctx =
Ctx {
token :: String,
endpointActivities :: String,
endpointTimeTrackingStart :: String,
httpLBSFunc :: MonadIO m => Request -> m (Response ByteString)
} deriving (Show)
i always get the error: Not in scope: type variable ‘m’
how can i define that function in my Ctx-data-type with its constraints?
i promise, that i will post my solution afterwards, when this last problem is solved
haskell dependency-injection
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
add a comment |
i get the basic functionality of the reader-monad from learnyouahaskell book and i've seen some advises here to make use of it for dependency-injection.
even there are some examples here on stackoverflow, i dont know how to use it for integration-testing.
my code is:
list :: Ctx -> [String] -> IO String
list ctx args = do
d <- eitherDecode <$> Uplink.get (token ctx) (endpointActivities ctx) :: IO (Either String Activities)
case d of
Left err -> return err
Right result -> return $ unlines . filterByPrefix (parsePrefix args) . extractNames $ activities result
uplink.hs
get :: String -> String -> IO B.ByteString
get token endpoint = do
req <- parseRequest endpoint
resp <- httpLBS $ withAuth token req
return $ getResponseBody resp
how can i mock the httpLBS - call for integration-testing with the reader-monad?
EDIT: !!!!
i almost have it now with the reader-monad. the only problem left is that i dont know how i can define that httpsLBS-function in my Ctx-data-type.
httpLBS-function-signature:
httpLBS :: MonadIO m => Request -> m (Response ByteString)
my Ctx data-type-definition:
data Ctx =
Ctx {
token :: String,
endpointActivities :: String,
endpointTimeTrackingStart :: String,
httpLBSFunc :: MonadIO m => Request -> m (Response ByteString)
} deriving (Show)
i always get the error: Not in scope: type variable ‘m’
how can i define that function in my Ctx-data-type with its constraints?
i promise, that i will post my solution afterwards, when this last problem is solved
haskell dependency-injection
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
1
I'm not sure I know what dependency injection really is, but why not parameterizegetby the http client function, like:get myHttpLBS token endpoint = do ....Readeris an abstraction around argument passing. I don't tend to reach for it unless both of: 1) I already have a monad stack, and 2) I have multiple top-level functions that call each other, and in particular I'd like to pass some value through a function, i.e. there is some function that does nothing but pass an argument to some other function. Other folks probably feel differently
– jberryman
Nov 13 '18 at 16:09
In functional programming, you can't use dependency injection because it makes everything impure. Instead, you compose functions, keeping as many of them pure as possible.
– Mark Seemann
Nov 13 '18 at 17:02
Did you writeuplink.hs? Don't hard-codehttpLBS; make it a parameter.
– chepner
Nov 13 '18 at 17:03
add a comment |
i get the basic functionality of the reader-monad from learnyouahaskell book and i've seen some advises here to make use of it for dependency-injection.
even there are some examples here on stackoverflow, i dont know how to use it for integration-testing.
my code is:
list :: Ctx -> [String] -> IO String
list ctx args = do
d <- eitherDecode <$> Uplink.get (token ctx) (endpointActivities ctx) :: IO (Either String Activities)
case d of
Left err -> return err
Right result -> return $ unlines . filterByPrefix (parsePrefix args) . extractNames $ activities result
uplink.hs
get :: String -> String -> IO B.ByteString
get token endpoint = do
req <- parseRequest endpoint
resp <- httpLBS $ withAuth token req
return $ getResponseBody resp
how can i mock the httpLBS - call for integration-testing with the reader-monad?
EDIT: !!!!
i almost have it now with the reader-monad. the only problem left is that i dont know how i can define that httpsLBS-function in my Ctx-data-type.
httpLBS-function-signature:
httpLBS :: MonadIO m => Request -> m (Response ByteString)
my Ctx data-type-definition:
data Ctx =
Ctx {
token :: String,
endpointActivities :: String,
endpointTimeTrackingStart :: String,
httpLBSFunc :: MonadIO m => Request -> m (Response ByteString)
} deriving (Show)
i always get the error: Not in scope: type variable ‘m’
how can i define that function in my Ctx-data-type with its constraints?
i promise, that i will post my solution afterwards, when this last problem is solved
haskell dependency-injection
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
i get the basic functionality of the reader-monad from learnyouahaskell book and i've seen some advises here to make use of it for dependency-injection.
even there are some examples here on stackoverflow, i dont know how to use it for integration-testing.
my code is:
list :: Ctx -> [String] -> IO String
list ctx args = do
d <- eitherDecode <$> Uplink.get (token ctx) (endpointActivities ctx) :: IO (Either String Activities)
case d of
Left err -> return err
Right result -> return $ unlines . filterByPrefix (parsePrefix args) . extractNames $ activities result
uplink.hs
get :: String -> String -> IO B.ByteString
get token endpoint = do
req <- parseRequest endpoint
resp <- httpLBS $ withAuth token req
return $ getResponseBody resp
how can i mock the httpLBS - call for integration-testing with the reader-monad?
EDIT: !!!!
i almost have it now with the reader-monad. the only problem left is that i dont know how i can define that httpsLBS-function in my Ctx-data-type.
httpLBS-function-signature:
httpLBS :: MonadIO m => Request -> m (Response ByteString)
my Ctx data-type-definition:
data Ctx =
Ctx {
token :: String,
endpointActivities :: String,
endpointTimeTrackingStart :: String,
httpLBSFunc :: MonadIO m => Request -> m (Response ByteString)
} deriving (Show)
i always get the error: Not in scope: type variable ‘m’
how can i define that function in my Ctx-data-type with its constraints?
i promise, that i will post my solution afterwards, when this last problem is solved
haskell dependency-injection
haskell dependency-injection
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
edited Nov 14 '18 at 21:49
stefa ng
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
asked Nov 13 '18 at 15:38
stefa ngstefa ng
7416
7416
1
I'm not sure I know what dependency injection really is, but why not parameterizegetby the http client function, like:get myHttpLBS token endpoint = do ....Readeris an abstraction around argument passing. I don't tend to reach for it unless both of: 1) I already have a monad stack, and 2) I have multiple top-level functions that call each other, and in particular I'd like to pass some value through a function, i.e. there is some function that does nothing but pass an argument to some other function. Other folks probably feel differently
– jberryman
Nov 13 '18 at 16:09
In functional programming, you can't use dependency injection because it makes everything impure. Instead, you compose functions, keeping as many of them pure as possible.
– Mark Seemann
Nov 13 '18 at 17:02
Did you writeuplink.hs? Don't hard-codehttpLBS; make it a parameter.
– chepner
Nov 13 '18 at 17:03
add a comment |
1
I'm not sure I know what dependency injection really is, but why not parameterizegetby the http client function, like:get myHttpLBS token endpoint = do ....Readeris an abstraction around argument passing. I don't tend to reach for it unless both of: 1) I already have a monad stack, and 2) I have multiple top-level functions that call each other, and in particular I'd like to pass some value through a function, i.e. there is some function that does nothing but pass an argument to some other function. Other folks probably feel differently
– jberryman
Nov 13 '18 at 16:09
In functional programming, you can't use dependency injection because it makes everything impure. Instead, you compose functions, keeping as many of them pure as possible.
– Mark Seemann
Nov 13 '18 at 17:02
Did you writeuplink.hs? Don't hard-codehttpLBS; make it a parameter.
– chepner
Nov 13 '18 at 17:03
1
1
I'm not sure I know what dependency injection really is, but why not parameterize
get by the http client function, like: get myHttpLBS token endpoint = do .... Reader is an abstraction around argument passing. I don't tend to reach for it unless both of: 1) I already have a monad stack, and 2) I have multiple top-level functions that call each other, and in particular I'd like to pass some value through a function, i.e. there is some function that does nothing but pass an argument to some other function. Other folks probably feel differently– jberryman
Nov 13 '18 at 16:09
I'm not sure I know what dependency injection really is, but why not parameterize
get by the http client function, like: get myHttpLBS token endpoint = do .... Reader is an abstraction around argument passing. I don't tend to reach for it unless both of: 1) I already have a monad stack, and 2) I have multiple top-level functions that call each other, and in particular I'd like to pass some value through a function, i.e. there is some function that does nothing but pass an argument to some other function. Other folks probably feel differently– jberryman
Nov 13 '18 at 16:09
In functional programming, you can't use dependency injection because it makes everything impure. Instead, you compose functions, keeping as many of them pure as possible.
– Mark Seemann
Nov 13 '18 at 17:02
In functional programming, you can't use dependency injection because it makes everything impure. Instead, you compose functions, keeping as many of them pure as possible.
– Mark Seemann
Nov 13 '18 at 17:02
Did you write
uplink.hs? Don't hard-code httpLBS; make it a parameter.– chepner
Nov 13 '18 at 17:03
Did you write
uplink.hs? Don't hard-code httpLBS; make it a parameter.– chepner
Nov 13 '18 at 17:03
add a comment |
1 Answer
1
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In Haskell, dependency injection is just higher order programming + currying. You can write your code as the following.
-- where (? -> ?) is the type of httpLBS
get_ :: (? -> ?) -> String -> String -> IO B.ByteString
get_ httpFunc token endpoint = do
req <- parseRequest endpoint
resp <- httpFunc $ withAuth token req
return $ getResponseBody resp
getProduction = get_ httpLBS
getTest = get_ httpMock
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
add a comment |
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active
oldest
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oldest
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In Haskell, dependency injection is just higher order programming + currying. You can write your code as the following.
-- where (? -> ?) is the type of httpLBS
get_ :: (? -> ?) -> String -> String -> IO B.ByteString
get_ httpFunc token endpoint = do
req <- parseRequest endpoint
resp <- httpFunc $ withAuth token req
return $ getResponseBody resp
getProduction = get_ httpLBS
getTest = get_ httpMock
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
add a comment |
In Haskell, dependency injection is just higher order programming + currying. You can write your code as the following.
-- where (? -> ?) is the type of httpLBS
get_ :: (? -> ?) -> String -> String -> IO B.ByteString
get_ httpFunc token endpoint = do
req <- parseRequest endpoint
resp <- httpFunc $ withAuth token req
return $ getResponseBody resp
getProduction = get_ httpLBS
getTest = get_ httpMock
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
add a comment |
In Haskell, dependency injection is just higher order programming + currying. You can write your code as the following.
-- where (? -> ?) is the type of httpLBS
get_ :: (? -> ?) -> String -> String -> IO B.ByteString
get_ httpFunc token endpoint = do
req <- parseRequest endpoint
resp <- httpFunc $ withAuth token req
return $ getResponseBody resp
getProduction = get_ httpLBS
getTest = get_ httpMock
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
In Haskell, dependency injection is just higher order programming + currying. You can write your code as the following.
-- where (? -> ?) is the type of httpLBS
get_ :: (? -> ?) -> String -> String -> IO B.ByteString
get_ httpFunc token endpoint = do
req <- parseRequest endpoint
resp <- httpFunc $ withAuth token req
return $ getResponseBody resp
getProduction = get_ httpLBS
getTest = get_ httpMock
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
answered Nov 13 '18 at 18:46
Izaak WeissIzaak Weiss
671510
671510
add a comment |
add a comment |
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1
I'm not sure I know what dependency injection really is, but why not parameterize
getby the http client function, like:get myHttpLBS token endpoint = do ....Readeris an abstraction around argument passing. I don't tend to reach for it unless both of: 1) I already have a monad stack, and 2) I have multiple top-level functions that call each other, and in particular I'd like to pass some value through a function, i.e. there is some function that does nothing but pass an argument to some other function. Other folks probably feel differently– jberryman
Nov 13 '18 at 16:09
In functional programming, you can't use dependency injection because it makes everything impure. Instead, you compose functions, keeping as many of them pure as possible.
– Mark Seemann
Nov 13 '18 at 17:02
Did you write
uplink.hs? Don't hard-codehttpLBS; make it a parameter.– chepner
Nov 13 '18 at 17:03