I have defined a type as:
type Register = Int
I'm also able to read in a list of numbers from a list of Strings using a function like:
readInt :: String -> Int
readInt s = read s :: Int
now, using readInt on a list like readInt "12 32 11" gives me [12, 32, 11] which is of type [Int].
My question is: instead of [Int], how can I get [Register].
I tried:
readRegister :: String -> Register
readRegister s = read s :: Register
but as I guessed, it doesn't seem to be valid syntax.
Your definition of Register is a type alias, i.e. it is interchangeable with its right hand side, i.e. here with Int.
But you state that readInt "12 32 11" would yield [12,32,11] :: [Int]. This is impossible given your type signature of readInt :: String -> Int. Perhaps you could show us a bit more of your code.
map readInt (words s) Now my readRegister code is readRegister :: String -> Register readRegister s = read s :: Register readRegisters s :: String -> [Register] readRegisters s = map readRegister (words s)Register is just another name for the type Int, it is the same type. The syntax
readRegister :: String -> Register
readRegister s = read s :: Register
is valid (but the type annotation on the read result is unnecessary). If it doesn't work, your compiler/interpreter is broken. Whether the type is displayed as Int or Register, however, may be surprising. It's not easy to predict when a type synonym is expanded and when not.
