No instance for Show (ejercicio mcm)

[flbulgarelli]

Hay un problema con el ejercicio de mcm.

El mcm definido así:

mcm a b = (a * b) / (gcd a b)

Arroja el siguiente error:

ム mcm 2 4

/tmp/compilation58:5:15:
No instance for (Show s0) arising from a use of ‘show’
The type variable ‘s0’ is ambiguous
Note: there are several potential instances:
instance Show Double -- Defined in ‘GHC.Float’
instance Show Float -- Defined in ‘GHC.Float’
instance (Integral a, Show a) => Show (GHC.Real.Ratio a)
-- Defined in ‘GHC.Real’
...plus 25 others
In the second argument of ‘(.)’, namely ‘show’
In the expression: putStr . show
In the expression: putStr . show $ mcm 2 4

/tmp/compilation58:5:22:
No instance for (Integral s0) arising from a use of ‘mcm’
The type variable ‘s0’ is ambiguous
Note: there are several potential instances:
instance Integral Int -- Defined in ‘GHC.Real’
instance Integral Integer -- Defined in ‘GHC.Real’
instance Integral GHC.Types.Word -- Defined in ‘GHC.Real’
In the second argument of ‘($)’, namely ‘mcm 2 4’
In the expression: putStr . show $ mcm 2 4
In an equation for ‘main’: main = putStr . show $ mcm 2 4

/tmp/compilation58:5:26:
No instance for (Num s0) arising from the literal ‘2’
The type variable ‘s0’ is ambiguous
Note: there are several potential instances:
instance Num Double -- Defined in ‘GHC.Float’
instance Num Float -- Defined in ‘GHC.Float’
instance Integral a => Num (GHC.Real.Ratio a)
-- Defined in ‘GHC.Real’
...plus three others
In the first argument of ‘mcm’, namely ‘2’
In the second argument of ‘($)’, namely ‘mcm 2 4’
In the expression: putStr . show $ mcm 2 4

[flbulgarelli]

Esto se deba probablemente a que en Mumuki hemos deshabilitado el checkeo de tipos de GHC. Por tanto, hay algunas expresiones cuyo tipo en runtime, al no tener la información estática de tipos, se vuelve ambiguo. La solución a este problema consiste en tipar explícitamente las expresiones ambiguas en los tests (por ejemplo, apendear a la expresión problemática un :: String o lo que fuere)