Why does Haskell not allow two data constructors to share "Const" and other defined data attributes?

Question

data Prop = Const Bool
          | Var Char
          | Not Prop
          | And Prop Prop
          | Imply Prop Prop

I am implementing the above data contructor with a minor addition,

data Prop = Const Bool
          | Var Char
          | Not Prop
          | Or Prop Prop
          | And Prop Prop
          | Imply Prop Prop

When I try to make another data contructor below that uses the previously defined constructor,

data Formula = Const Bool
          | Var Prop
          | Not Formula
          | And Formula Formula
          | Or Formula Formula
          | Imply Formula Formula

I get this error: "Multiple declarations of 'Const'"

The same error follows with Not, And, Imply, and Or. Why does Haskell not allow this?

Answer 1

Haskell doesn't allow this because it would be ambiguous. The value constructor Prop is effectively a function, which may be clearer if you ask GHCi about its type:

> :t Const
Const :: Bool -> Prop

If you attempt to add one more Const constructor in the same module, you'd have two 'functions' called Const in the same module. You can't have that.