Haskell transfer between monadic functions
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Feel I am never going to fully grasp Haskell now. Two functions: one that counts records in a SQlite DB, so it can produce incremental IDs (checkUniqueID). The other one to make the records, calling on checkUniqueID. I just need the value over to taskEntry as an Int. I guess I am missing the knowledge to stay in the monadic realm. Code below.
-- checkUniqueID :: IO ()
checkUniqueID = do
conn <- open "taglist.db"
len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int]
let showLength = Data.List.length $ len
close conn
return (showLength + 1) -- for testing purposes
-- fieldnames: id, task, date_in, date_out
taskEntry :: IO ()
taskEntry = do
putStrLn "Provide task and date due: "
let taskIDInt = checkUniqueID -- issue here!
task <- getLine
date_out <- getLine
let date_in = "today"
conn <- open "taglist.db"
execute conn "INSERT INTO task (id, task, date_in, date_out) VALUES (?,?,?,?)"
(taskIDInt :: Int , task :: String , date_in :: String , date_out :: String)
close conn
return ()
sqlite haskell io monads
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
add a comment |
Feel I am never going to fully grasp Haskell now. Two functions: one that counts records in a SQlite DB, so it can produce incremental IDs (checkUniqueID). The other one to make the records, calling on checkUniqueID. I just need the value over to taskEntry as an Int. I guess I am missing the knowledge to stay in the monadic realm. Code below.
-- checkUniqueID :: IO ()
checkUniqueID = do
conn <- open "taglist.db"
len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int]
let showLength = Data.List.length $ len
close conn
return (showLength + 1) -- for testing purposes
-- fieldnames: id, task, date_in, date_out
taskEntry :: IO ()
taskEntry = do
putStrLn "Provide task and date due: "
let taskIDInt = checkUniqueID -- issue here!
task <- getLine
date_out <- getLine
let date_in = "today"
conn <- open "taglist.db"
execute conn "INSERT INTO task (id, task, date_in, date_out) VALUES (?,?,?,?)"
(taskIDInt :: Int , task :: String , date_in :: String , date_out :: String)
close conn
return ()
sqlite haskell io monads
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
3
for starters, the type should probably becheckUniqueID :: IO Int- you actually want to return something of typeInt, besides executing an IO action. Then:taskIDInt <- checkUniqueID, becausecheckUniqueIDis in IO.
– mb21
Nov 23 '18 at 16:04
add a comment |
Feel I am never going to fully grasp Haskell now. Two functions: one that counts records in a SQlite DB, so it can produce incremental IDs (checkUniqueID). The other one to make the records, calling on checkUniqueID. I just need the value over to taskEntry as an Int. I guess I am missing the knowledge to stay in the monadic realm. Code below.
-- checkUniqueID :: IO ()
checkUniqueID = do
conn <- open "taglist.db"
len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int]
let showLength = Data.List.length $ len
close conn
return (showLength + 1) -- for testing purposes
-- fieldnames: id, task, date_in, date_out
taskEntry :: IO ()
taskEntry = do
putStrLn "Provide task and date due: "
let taskIDInt = checkUniqueID -- issue here!
task <- getLine
date_out <- getLine
let date_in = "today"
conn <- open "taglist.db"
execute conn "INSERT INTO task (id, task, date_in, date_out) VALUES (?,?,?,?)"
(taskIDInt :: Int , task :: String , date_in :: String , date_out :: String)
close conn
return ()
sqlite haskell io monads
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
Feel I am never going to fully grasp Haskell now. Two functions: one that counts records in a SQlite DB, so it can produce incremental IDs (checkUniqueID). The other one to make the records, calling on checkUniqueID. I just need the value over to taskEntry as an Int. I guess I am missing the knowledge to stay in the monadic realm. Code below.
-- checkUniqueID :: IO ()
checkUniqueID = do
conn <- open "taglist.db"
len <- query_ conn "SELECT (id) FROM task" :: IO [Only Int]
let showLength = Data.List.length $ len
close conn
return (showLength + 1) -- for testing purposes
-- fieldnames: id, task, date_in, date_out
taskEntry :: IO ()
taskEntry = do
putStrLn "Provide task and date due: "
let taskIDInt = checkUniqueID -- issue here!
task <- getLine
date_out <- getLine
let date_in = "today"
conn <- open "taglist.db"
execute conn "INSERT INTO task (id, task, date_in, date_out) VALUES (?,?,?,?)"
(taskIDInt :: Int , task :: String , date_in :: String , date_out :: String)
close conn
return ()
sqlite haskell io monads
sqlite haskell io monads
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
asked Nov 23 '18 at 16:00
MadderoteMadderote
352211
352211
3
for starters, the type should probably becheckUniqueID :: IO Int- you actually want to return something of typeInt, besides executing an IO action. Then:taskIDInt <- checkUniqueID, becausecheckUniqueIDis in IO.
– mb21
Nov 23 '18 at 16:04
add a comment |
3
for starters, the type should probably becheckUniqueID :: IO Int- you actually want to return something of typeInt, besides executing an IO action. Then:taskIDInt <- checkUniqueID, becausecheckUniqueIDis in IO.
– mb21
Nov 23 '18 at 16:04
3
3
for starters, the type should probably be
checkUniqueID :: IO Int - you actually want to return something of type Int, besides executing an IO action. Then: taskIDInt <- checkUniqueID, because checkUniqueID is in IO.– mb21
Nov 23 '18 at 16:04
for starters, the type should probably be
checkUniqueID :: IO Int - you actually want to return something of type Int, besides executing an IO action. Then: taskIDInt <- checkUniqueID, because checkUniqueID is in IO.– mb21
Nov 23 '18 at 16:04
add a comment |
1 Answer
1
active
oldest
votes
First, checkUniqueID returns an Int, so its type should be IO Int, not IO ():
checkUniqueID :: IO Int
Second, within the do notation, the left arrow <- is what binds result of a monadic function to a name. You're already using it with getLine, so I'm not entirely sure why you would fail to use it with checkUniqueID as well:
taskIDInt <- checkUniqueID
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
First, checkUniqueID returns an Int, so its type should be IO Int, not IO ():
checkUniqueID :: IO Int
Second, within the do notation, the left arrow <- is what binds result of a monadic function to a name. You're already using it with getLine, so I'm not entirely sure why you would fail to use it with checkUniqueID as well:
taskIDInt <- checkUniqueID
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
add a comment |
First, checkUniqueID returns an Int, so its type should be IO Int, not IO ():
checkUniqueID :: IO Int
Second, within the do notation, the left arrow <- is what binds result of a monadic function to a name. You're already using it with getLine, so I'm not entirely sure why you would fail to use it with checkUniqueID as well:
taskIDInt <- checkUniqueID
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
add a comment |
First, checkUniqueID returns an Int, so its type should be IO Int, not IO ():
checkUniqueID :: IO Int
Second, within the do notation, the left arrow <- is what binds result of a monadic function to a name. You're already using it with getLine, so I'm not entirely sure why you would fail to use it with checkUniqueID as well:
taskIDInt <- checkUniqueID
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
First, checkUniqueID returns an Int, so its type should be IO Int, not IO ():
checkUniqueID :: IO Int
Second, within the do notation, the left arrow <- is what binds result of a monadic function to a name. You're already using it with getLine, so I'm not entirely sure why you would fail to use it with checkUniqueID as well:
taskIDInt <- checkUniqueID
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
answered Nov 23 '18 at 16:20
Fyodor SoikinFyodor Soikin
43.8k569102
43.8k569102
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
add a comment |
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
I am not failing with your suggestion. I have a hard time seeing the forrest through the trees. You put me on the right track and it works! Sorry for this... Sometimes I feel a bit stupid trying monoids, applicatives, functors etc while the only thing I need to do is a simple bind of two monadic functions! Thanks
– Madderote
Nov 23 '18 at 19:02
add a comment |
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for starters, the type should probably be
checkUniqueID :: IO Int- you actually want to return something of typeInt, besides executing an IO action. Then:taskIDInt <- checkUniqueID, becausecheckUniqueIDis in IO.– mb21
Nov 23 '18 at 16:04