# The `monomorphic`

library

## What is this?

This library provides the type-class and functions to convert polymorphic data-types to/from its monomorphic representation types.
It is convenient to provide a monomorphic interface for dependently-typed programs.

## Usage

Consider the following example:

```
data Nat = Z | S Nat
data SNat (n :: Nat) where
SZ :: SNat Z
SS :: SNat n -> SNat (S n)
instance Monomorphicable SNat where
type MonomorphicRep SNat = Int
promote 0 = Monomorphic SZ
promote n
| n < 0 = error "negative number"
| otherwise =
case promote (n - 1) of
Monomorphic sn -> Monomorphic (SS sn)
demote (Monomorphic sn) = toInt sn
data Vector (a :: *) (n :: Nat) where
VNil :: Vector a Z
(:-) :: a -> Vector a n -> Vector a (S n)
instance Monomorphicable (Vector a) whre
type MonomorphicRep (Vector a) = [a]
demote (Monomorphic n) = toList n
promote [] = Monomorphic Nil
promote (x:xs) =
case promote xs of
Monomorphic xs' -> Monomorphic $ x :- xs'
```

`Monomorphic k`

is the wrapper type to eliminate the polymorphic part of the types.
The `Monomorphicable`

type-class provides the functions to convert polymorphic value from/to its monomorphic representation, say `MonomorphicRep k`

associated type.

In the example above, `SNat n`

can be monomorphically represented by `Int`

.
There are some convenient functions to manipulate monomorphic types and functions. For more detail, see API documentation.