[Haskell-cafe] Predicates in data types

[Navid Hallajian]

Hello,

I'm a beginner in Haskell, so forgive me if this is a basic question, but
I'd like to know if it's possible to have a predicate as part of a data
type, so that when the data type is created, it can only be done if it
satisfies the predicate else a type error is thrown.

For instance, a matrix with integer elements could be modelled as [[Int]],
given the restrictions that

   - it must have at least one column and one row (so there must be at
   least one list), and
   - every list must have the same length

so that when a matrix is created, the type system wont allow it if the
predicates aren't met.

Thanks,

Navid
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