Generate choose on custom data type with 2 options
I am trying to achieve something very simple.
I have this data type :
import Test.QuickCheck
import System.Random
data Letter = G | B deriving(Show, Eq, Bounded)
arbitraryLetter :: Gen Letter
arbitraryLetter = choose (G,B)
I am compiling and getting this error
• No instance for (Random Letter) arising from a use of ‘choose’
• In the expression: choose (G, B)
In an equation for ‘arbitraryLetter’:
arbitraryLetter = choose (G, B)
Why isn't this working?
I want to be able to use QuickCheck on this data type.
haskell quickcheck
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
add a comment |
I am trying to achieve something very simple.
I have this data type :
import Test.QuickCheck
import System.Random
data Letter = G | B deriving(Show, Eq, Bounded)
arbitraryLetter :: Gen Letter
arbitraryLetter = choose (G,B)
I am compiling and getting this error
• No instance for (Random Letter) arising from a use of ‘choose’
• In the expression: choose (G, B)
In an equation for ‘arbitraryLetter’:
arbitraryLetter = choose (G, B)
Why isn't this working?
I want to be able to use QuickCheck on this data type.
haskell quickcheck
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
add a comment |
I am trying to achieve something very simple.
I have this data type :
import Test.QuickCheck
import System.Random
data Letter = G | B deriving(Show, Eq, Bounded)
arbitraryLetter :: Gen Letter
arbitraryLetter = choose (G,B)
I am compiling and getting this error
• No instance for (Random Letter) arising from a use of ‘choose’
• In the expression: choose (G, B)
In an equation for ‘arbitraryLetter’:
arbitraryLetter = choose (G, B)
Why isn't this working?
I want to be able to use QuickCheck on this data type.
haskell quickcheck
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
I am trying to achieve something very simple.
I have this data type :
import Test.QuickCheck
import System.Random
data Letter = G | B deriving(Show, Eq, Bounded)
arbitraryLetter :: Gen Letter
arbitraryLetter = choose (G,B)
I am compiling and getting this error
• No instance for (Random Letter) arising from a use of ‘choose’
• In the expression: choose (G, B)
In an equation for ‘arbitraryLetter’:
arbitraryLetter = choose (G, B)
Why isn't this working?
I want to be able to use QuickCheck on this data type.
haskell quickcheck
haskell quickcheck
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
asked Nov 24 '18 at 13:12
EyzukyEyzuky
7741024
7741024
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
choose has type Random a => (a, a) -> Gen a, so choose (G, B) requires a Random instance for your Letter type. If you want to create a generator from a set of values you can use elements instead:
arbitraryLetter :: Gen Letter
arbitraryLetter = elements [G, B]
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
1
@Eyzuky - You can usesamplein ghci:sample arbitraryLetter.
– Lee
Nov 24 '18 at 14:20
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
choose has type Random a => (a, a) -> Gen a, so choose (G, B) requires a Random instance for your Letter type. If you want to create a generator from a set of values you can use elements instead:
arbitraryLetter :: Gen Letter
arbitraryLetter = elements [G, B]
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
1
@Eyzuky - You can usesamplein ghci:sample arbitraryLetter.
– Lee
Nov 24 '18 at 14:20
add a comment |
choose has type Random a => (a, a) -> Gen a, so choose (G, B) requires a Random instance for your Letter type. If you want to create a generator from a set of values you can use elements instead:
arbitraryLetter :: Gen Letter
arbitraryLetter = elements [G, B]
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
1
@Eyzuky - You can usesamplein ghci:sample arbitraryLetter.
– Lee
Nov 24 '18 at 14:20
add a comment |
choose has type Random a => (a, a) -> Gen a, so choose (G, B) requires a Random instance for your Letter type. If you want to create a generator from a set of values you can use elements instead:
arbitraryLetter :: Gen Letter
arbitraryLetter = elements [G, B]
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
choose has type Random a => (a, a) -> Gen a, so choose (G, B) requires a Random instance for your Letter type. If you want to create a generator from a set of values you can use elements instead:
arbitraryLetter :: Gen Letter
arbitraryLetter = elements [G, B]
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
answered Nov 24 '18 at 13:26
LeeLee
119k14175245
119k14175245
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
1
@Eyzuky - You can usesamplein ghci:sample arbitraryLetter.
– Lee
Nov 24 '18 at 14:20
add a comment |
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
1
@Eyzuky - You can usesamplein ghci:sample arbitraryLetter.
– Lee
Nov 24 '18 at 14:20
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
Thanks, How do I generate 1 and print to the console? I tried running arbitraryLetter and got an error : • No instance for (Show (Gen Letter)) arising from a use of ‘print’ • In a stmt of an interactive GHCi command: print it
– Eyzuky
Nov 24 '18 at 13:47
1
1
@Eyzuky - You can use
sample in ghci: sample arbitraryLetter.– Lee
Nov 24 '18 at 14:20
@Eyzuky - You can use
sample in ghci: sample arbitraryLetter.– Lee
Nov 24 '18 at 14:20
add a comment |
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