Haskell mapM_ to other format
Although I have the feeling I am progressing in Haskell I am still not a hundred percent comfortable with contexts. Take the code here:
extractData :: IO ()
extractData = do
id <- getLine
let userToolIDSelect = (read id) :: Int
connection <- open "tools.db"
resp <- query connection "SELECT * FROM tools WHERE toolID = (?);"
(Only userToolIDSelect) :: IO [Tool]
mapM_ print resp
Works fine, but how I can use mapM_ to generate something I can work with? I can only get it to print to the console, but I would like to have eg. a list back so I can write it to a file and import it in another file for processing...
The number of possibilities and libraries in Haskell dazzles me a bit and makes me loose focus sometimes. Think this is that time again..
haskell io
edited Nov 15 '18 at 13:39
duplode
23k44987
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
add a comment |
Although I have the feeling I am progressing in Haskell I am still not a hundred percent comfortable with contexts. Take the code here:
extractData :: IO ()
extractData = do
id <- getLine
let userToolIDSelect = (read id) :: Int
connection <- open "tools.db"
resp <- query connection "SELECT * FROM tools WHERE toolID = (?);"
(Only userToolIDSelect) :: IO [Tool]
mapM_ print resp
Works fine, but how I can use mapM_ to generate something I can work with? I can only get it to print to the console, but I would like to have eg. a list back so I can write it to a file and import it in another file for processing...
The number of possibilities and libraries in Haskell dazzles me a bit and makes me loose focus sometimes. Think this is that time again..
haskell io
edited Nov 15 '18 at 13:39
duplode
23k44987
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
This is too vague. You want to replacemapM_with "something I can work with", which could be anything at all. You should clarify your goal. Note that you already have a list:resp. You can work with that withoutmapM_, if you want. E.g. you can writerespto a file.
– chi
Nov 15 '18 at 12:48
If you need to work with mutable structure, e.g. STArray, you may find that the functions like mapM_, forM_ or etc are useful.
– assembly.jc
Nov 15 '18 at 14:01
add a comment |
Although I have the feeling I am progressing in Haskell I am still not a hundred percent comfortable with contexts. Take the code here:
extractData :: IO ()
extractData = do
id <- getLine
let userToolIDSelect = (read id) :: Int
connection <- open "tools.db"
resp <- query connection "SELECT * FROM tools WHERE toolID = (?);"
(Only userToolIDSelect) :: IO [Tool]
mapM_ print resp
Works fine, but how I can use mapM_ to generate something I can work with? I can only get it to print to the console, but I would like to have eg. a list back so I can write it to a file and import it in another file for processing...
The number of possibilities and libraries in Haskell dazzles me a bit and makes me loose focus sometimes. Think this is that time again..
haskell io
edited Nov 15 '18 at 13:39
duplode
23k44987
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
Although I have the feeling I am progressing in Haskell I am still not a hundred percent comfortable with contexts. Take the code here:
extractData :: IO ()
extractData = do
id <- getLine
let userToolIDSelect = (read id) :: Int
connection <- open "tools.db"
resp <- query connection "SELECT * FROM tools WHERE toolID = (?);"
(Only userToolIDSelect) :: IO [Tool]
mapM_ print resp
Works fine, but how I can use mapM_ to generate something I can work with? I can only get it to print to the console, but I would like to have eg. a list back so I can write it to a file and import it in another file for processing...
The number of possibilities and libraries in Haskell dazzles me a bit and makes me loose focus sometimes. Think this is that time again..
haskell io
haskell io
edited Nov 15 '18 at 13:39
duplode
23k44987
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
edited Nov 15 '18 at 13:39
duplode
23k44987
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
edited Nov 15 '18 at 13:39
duplode
23k44987
edited Nov 15 '18 at 13:39
duplode
23k44987
edited Nov 15 '18 at 13:39
duplode
23k44987
23k44987
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
asked Nov 15 '18 at 12:17
MadderoteMadderote
271111
271111
This is too vague. You want to replacemapM_with "something I can work with", which could be anything at all. You should clarify your goal. Note that you already have a list:resp. You can work with that withoutmapM_, if you want. E.g. you can writerespto a file.
– chi
Nov 15 '18 at 12:48
If you need to work with mutable structure, e.g. STArray, you may find that the functions like mapM_, forM_ or etc are useful.
– assembly.jc
Nov 15 '18 at 14:01
add a comment |
This is too vague. You want to replacemapM_with "something I can work with", which could be anything at all. You should clarify your goal. Note that you already have a list:resp. You can work with that withoutmapM_, if you want. E.g. you can writerespto a file.
– chi
Nov 15 '18 at 12:48
If you need to work with mutable structure, e.g. STArray, you may find that the functions like mapM_, forM_ or etc are useful.
– assembly.jc
Nov 15 '18 at 14:01
This is too vague. You want to replace
mapM_ with "something I can work with", which could be anything at all. You should clarify your goal. Note that you already have a list: resp. You can work with that without mapM_, if you want. E.g. you can write resp to a file.– chi
Nov 15 '18 at 12:48
This is too vague. You want to replace
mapM_ with "something I can work with", which could be anything at all. You should clarify your goal. Note that you already have a list: resp. You can work with that without mapM_, if you want. E.g. you can write resp to a file.– chi
Nov 15 '18 at 12:48
If you need to work with mutable structure, e.g. STArray, you may find that the functions like mapM_, forM_ or etc are useful.
– assembly.jc
Nov 15 '18 at 14:01
If you need to work with mutable structure, e.g. STArray, you may find that the functions like mapM_, forM_ or etc are useful.
– assembly.jc
Nov 15 '18 at 14:01
add a comment |
1 Answer
1
active
oldest
votes
Well, you just pass a function you want instead of print. Either using lambda, for simple things:
mapM_ (tool -> ...) resp
or as separate IO action:
doSomethingWithTool :: Tool -> IO ()
doSomethingWithTool tool = do
...
return ()
and then
mapM_ doSomethingWithTool resp
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
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votes
Well, you just pass a function you want instead of print. Either using lambda, for simple things:
mapM_ (tool -> ...) resp
or as separate IO action:
doSomethingWithTool :: Tool -> IO ()
doSomethingWithTool tool = do
...
return ()
and then
mapM_ doSomethingWithTool resp
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
add a comment |
Well, you just pass a function you want instead of print. Either using lambda, for simple things:
mapM_ (tool -> ...) resp
or as separate IO action:
doSomethingWithTool :: Tool -> IO ()
doSomethingWithTool tool = do
...
return ()
and then
mapM_ doSomethingWithTool resp
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
add a comment |
Well, you just pass a function you want instead of print. Either using lambda, for simple things:
mapM_ (tool -> ...) resp
or as separate IO action:
doSomethingWithTool :: Tool -> IO ()
doSomethingWithTool tool = do
...
return ()
and then
mapM_ doSomethingWithTool resp
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
Well, you just pass a function you want instead of print. Either using lambda, for simple things:
mapM_ (tool -> ...) resp
or as separate IO action:
doSomethingWithTool :: Tool -> IO ()
doSomethingWithTool tool = do
...
return ()
and then
mapM_ doSomethingWithTool resp
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
answered Nov 15 '18 at 12:47
arrowdarrowd
22.8k45483
22.8k45483
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
add a comment |
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
@chi: it is vague. Sorry. [at]Arrowd understood. That was the answer I was looking for. Was trying to get it out of the Monad, but then realized that that is impossible.
– Madderote
Nov 15 '18 at 15:59
add a comment |
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This is too vague. You want to replace
mapM_with "something I can work with", which could be anything at all. You should clarify your goal. Note that you already have a list:resp. You can work with that withoutmapM_, if you want. E.g. you can writerespto a file.– chi
Nov 15 '18 at 12:48
If you need to work with mutable structure, e.g. STArray, you may find that the functions like mapM_, forM_ or etc are useful.
– assembly.jc
Nov 15 '18 at 14:01