Unresolved overloading - trying to make an instance for Int for own class
I have a class which pre-implements one function (by now) and I want to use it via Instances, I started with Int, which didnt work.
It compiles, but when i try to call the function with fac 3,
I get the following ERROR:
Unresolved overloading
* Type : Fibo a => a
* Expression : fac 3
class (Eq a, Ord a, Show a, Num a) => Fibo a where
fac :: a -> a
fac n
| n == 0 = 1
| otherwise = n * fac (n-1)
instance Fibo Int where
fac n = fac n
I cannot understand why it isnt working for my class with Int when its working for Show with a new type like:
newtype IN_0 = IN_0 Int
instance Show IN_0 where
show (IN_0 n) = show n
At least i think that the misstake is in the instance part, I thought that all i need to do is removing the constructor and replacing the name...
Is something missing, can u tell me the difference of that what i did for show and why it didnt work for my own class?
haskell typeclass
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
add a comment |
I have a class which pre-implements one function (by now) and I want to use it via Instances, I started with Int, which didnt work.
It compiles, but when i try to call the function with fac 3,
I get the following ERROR:
Unresolved overloading
* Type : Fibo a => a
* Expression : fac 3
class (Eq a, Ord a, Show a, Num a) => Fibo a where
fac :: a -> a
fac n
| n == 0 = 1
| otherwise = n * fac (n-1)
instance Fibo Int where
fac n = fac n
I cannot understand why it isnt working for my class with Int when its working for Show with a new type like:
newtype IN_0 = IN_0 Int
instance Show IN_0 where
show (IN_0 n) = show n
At least i think that the misstake is in the instance part, I thought that all i need to do is removing the constructor and replacing the name...
Is something missing, can u tell me the difference of that what i did for show and why it didnt work for my own class?
haskell typeclass
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
add a comment |
I have a class which pre-implements one function (by now) and I want to use it via Instances, I started with Int, which didnt work.
It compiles, but when i try to call the function with fac 3,
I get the following ERROR:
Unresolved overloading
* Type : Fibo a => a
* Expression : fac 3
class (Eq a, Ord a, Show a, Num a) => Fibo a where
fac :: a -> a
fac n
| n == 0 = 1
| otherwise = n * fac (n-1)
instance Fibo Int where
fac n = fac n
I cannot understand why it isnt working for my class with Int when its working for Show with a new type like:
newtype IN_0 = IN_0 Int
instance Show IN_0 where
show (IN_0 n) = show n
At least i think that the misstake is in the instance part, I thought that all i need to do is removing the constructor and replacing the name...
Is something missing, can u tell me the difference of that what i did for show and why it didnt work for my own class?
haskell typeclass
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
I have a class which pre-implements one function (by now) and I want to use it via Instances, I started with Int, which didnt work.
It compiles, but when i try to call the function with fac 3,
I get the following ERROR:
Unresolved overloading
* Type : Fibo a => a
* Expression : fac 3
class (Eq a, Ord a, Show a, Num a) => Fibo a where
fac :: a -> a
fac n
| n == 0 = 1
| otherwise = n * fac (n-1)
instance Fibo Int where
fac n = fac n
I cannot understand why it isnt working for my class with Int when its working for Show with a new type like:
newtype IN_0 = IN_0 Int
instance Show IN_0 where
show (IN_0 n) = show n
At least i think that the misstake is in the instance part, I thought that all i need to do is removing the constructor and replacing the name...
Is something missing, can u tell me the difference of that what i did for show and why it didnt work for my own class?
haskell typeclass
haskell typeclass
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
edited Nov 15 '18 at 3:22
Lorem2979
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
asked Nov 15 '18 at 0:09
Lorem2979Lorem2979
84
84
add a comment |
add a comment |
1 Answer
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As far as I can see there are two problems.
Firstly you need to write fac (3 :: Int) in order to disambiguate the type of 3. That will get you rid of the type error.
Secondly you need to get rid of the line fac n = fac n in your instance definition. That results in an undefined method. Rather leaving the instance definition empty results in the default instance being used.
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
Thank you for your fast answer, I removed thefac n = fac nline. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...
– Lorem2979
Nov 15 '18 at 1:28
Indeed I understand it is a test. Nonetheless my point was you should need write that call asfac (3::Int)instead to specify that the literal3is of typeInt, rather than say anInteger.
– Jorge Adriano
Nov 15 '18 at 1:36
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
add a comment |
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As far as I can see there are two problems.
Firstly you need to write fac (3 :: Int) in order to disambiguate the type of 3. That will get you rid of the type error.
Secondly you need to get rid of the line fac n = fac n in your instance definition. That results in an undefined method. Rather leaving the instance definition empty results in the default instance being used.
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
Thank you for your fast answer, I removed thefac n = fac nline. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...
– Lorem2979
Nov 15 '18 at 1:28
Indeed I understand it is a test. Nonetheless my point was you should need write that call asfac (3::Int)instead to specify that the literal3is of typeInt, rather than say anInteger.
– Jorge Adriano
Nov 15 '18 at 1:36
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
add a comment |
As far as I can see there are two problems.
Firstly you need to write fac (3 :: Int) in order to disambiguate the type of 3. That will get you rid of the type error.
Secondly you need to get rid of the line fac n = fac n in your instance definition. That results in an undefined method. Rather leaving the instance definition empty results in the default instance being used.
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
Thank you for your fast answer, I removed thefac n = fac nline. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...
– Lorem2979
Nov 15 '18 at 1:28
Indeed I understand it is a test. Nonetheless my point was you should need write that call asfac (3::Int)instead to specify that the literal3is of typeInt, rather than say anInteger.
– Jorge Adriano
Nov 15 '18 at 1:36
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
add a comment |
As far as I can see there are two problems.
Firstly you need to write fac (3 :: Int) in order to disambiguate the type of 3. That will get you rid of the type error.
Secondly you need to get rid of the line fac n = fac n in your instance definition. That results in an undefined method. Rather leaving the instance definition empty results in the default instance being used.
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
As far as I can see there are two problems.
Firstly you need to write fac (3 :: Int) in order to disambiguate the type of 3. That will get you rid of the type error.
Secondly you need to get rid of the line fac n = fac n in your instance definition. That results in an undefined method. Rather leaving the instance definition empty results in the default instance being used.
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
answered Nov 15 '18 at 1:05
Jorge AdrianoJorge Adriano
2,219919
2,219919
Thank you for your fast answer, I removed thefac n = fac nline. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...
– Lorem2979
Nov 15 '18 at 1:28
Indeed I understand it is a test. Nonetheless my point was you should need write that call asfac (3::Int)instead to specify that the literal3is of typeInt, rather than say anInteger.
– Jorge Adriano
Nov 15 '18 at 1:36
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
add a comment |
Thank you for your fast answer, I removed thefac n = fac nline. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...
– Lorem2979
Nov 15 '18 at 1:28
Indeed I understand it is a test. Nonetheless my point was you should need write that call asfac (3::Int)instead to specify that the literal3is of typeInt, rather than say anInteger.
– Jorge Adriano
Nov 15 '18 at 1:36
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
Thank you for your fast answer, I removed the
fac n = fac n line. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...– Lorem2979
Nov 15 '18 at 1:28
Thank you for your fast answer, I removed the
fac n = fac n line. But fac 3 was just a test, calling the function with the Value 3. When ever i wrote a function until now I could call it like that...– Lorem2979
Nov 15 '18 at 1:28
Indeed I understand it is a test. Nonetheless my point was you should need write that call as
fac (3::Int) instead to specify that the literal 3 is of type Int, rather than say an Integer.– Jorge Adriano
Nov 15 '18 at 1:36
Indeed I understand it is a test. Nonetheless my point was you should need write that call as
fac (3::Int) instead to specify that the literal 3 is of type Int, rather than say an Integer.– Jorge Adriano
Nov 15 '18 at 1:36
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
Thank you very much, I remember what (3::Int) means.
– Lorem2979
Nov 15 '18 at 1:41
add a comment |
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