In addition to fixing 'Float', you should define the 'Fractional' instance
for MathExpression. This would let you use:
let pi = 3.14 :: MathExpression
So your instance of Fractional would look like:
instance Num MathExpression where
(+) a b = Add a b
(*) a b = Multiply a b
(-) a b = Sub
Your MathExpression data type has nothing to do with numbers of any kind. Your
"Float" data constructor doesn't mean that float numbers are a part of your
type; instead it means that you have a SINGLE value of type MathExpression, and
this value is named "Float".
You should modify your data dec
Others have pointed out your first bug.
To get floating-point numeric literals you will need to define
instances of Num and then Fractional for your symbolic type.
On 19 August 2011 21:40, Paul Reiners wrote:
> *Main> let pi = 3.14 :: MathExpression
>
__
On Fri, Aug 19, 2011 at 1:45 PM, Thomas DuBuisson
wrote:
> This is not a valid data declaration. You can't have a "Float" field
> without any constructor name and have it still of type
And the reason why it accepts 'data MathExpr = Float', is because data
constructors and types live in separate
This is not a valid data declaration. You can't have a "Float" field
without any constructor name and have it still of type
"MathExpression". I suggest you do something like:
data MathExpr = MathFloat Float
So you may declare pi:
let mathPi = MathFloat pi -- note "pi" is defined
