... since it's not used in the `Dhall.Core` module at all

The old list-based implementation was tuned for Morte and more efficient for
type-checking typic...

The error messages alone warranted separating this out into a separate module

In other words, instead of writing:

let f (x : Natural) = x + 1
in ...

... you must n...

Example usage:

let handlers = { Left = Natural/even, Right = \(x : Bool) -> x }
in ...

This reverts commit 98ef584a67f80ba7d1fdfa67a3446f2b96653228.

This can be implemented in terms of `List/build` and `List/fold`, and those
permit build/fold fu...

This is easier on the eyes when writing out sums of products, like:

< Just = { foo = 1, bar...

Also, replace the `|` with `,` for union types and literals

Note that I haven't even implemented union literals, so this can't even be used,
yet!

This lets...

This ensures that `<>` unambiguously refers to the empty sum type

There are two main reasons that I'm removing `(++)`:

* I would like to use `(++)` instead of `(...

The original motivation for adding `Text/concat` was to work around the
quadratic time complexit...

This is more efficient since the only thing we ever do is concatenate text,
which `Builder` is o...

Just the types for now. No union literals or pattern matching, yet

This reverts commit 954e8619b68be470f9995440d563ac90adbc6331.

The simpler approach still permitted variable capture. For example, this would
break:

\x -...

You can implement `List/index` equally efficiently in terms of `List/drop` and
`List/first`

This eliminates the need for double braces

... but this time using a syntax similar to `List` literals

Move the type annotation outside the list

This is to prepare for an equivalent syntax for `Mayb...