Lint

Automatically improve a Dhall expression

Currently this:

• removes unused let bindings with removeUnusedBindings.
• fixes let a = x ≡ y to be let a = assert : x ≡ y
• consolidates nested let bindings to use a multiple-let binding with removeLetInLet
• fixes paths of the form ./../foo to ../foo
• Replaces deprecated Optional/fold and Optional/build built-ins

Remove unused Let bindings.

Fix Let bindings that the user probably meant to be asserts

This transforms ./../foo into ../foo

The difference between

let x = 1 let y = 2 in x + y

and

let x = 1 in let y = 2 in x + y

is that in the second expression, the inner Let is wrapped by a Note.

We remove such a Note in order to consolidate nested let-blocks into a single one.

This replaces Optional/fold and Optional/build, both of which can be implemented within the language

This replaces a saturated Optional/fold with the equivalent merge expression