unison/unison-src/transcripts/fix2254.md

.a> builtins.merge

This transcript checks that updates to data types propagate successfully to dependent types and dependent terms that do pattern matching. First let's create some types and terms:

unique type A a b c d
  = A a
  | B b
  | C c
  | D d

structural type NeedsA a b = NeedsA (A a b Nat Nat)
                | Zoink Text

f : A Nat Nat Nat Nat -> Nat
f = cases
  A n -> n
  _ -> 42

f2 a =
  n = f a
  n + 1

f3 : NeedsA Nat Nat -> Nat
f3 = cases
  NeedsA a -> f a + 20
  _ -> 0

g : A Nat Nat Nat Nat -> Nat
g = cases
  D n -> n
  _ -> 43

We'll make our edits in a fork of the a namespace:

.a> add
.> fork a a2

First let's edit the A type, adding another constructor E. Note that the functions written against the old type have a wildcard in their pattern match, so they should work fine after the update.

unique type A a b c d
  = A a
  | B b
  | C c
  | D d
  | E a d

Let's do the update now, and verify that the definitions all look good and there's nothing todo:

.a2> update.old
.a2> view A NeedsA f f2 f3 g
.a2> todo

.a2> builtins.merge

Record updates

Here's a test of updating a record:

structural type Rec = { uno : Nat, dos : Nat }

combine r = uno r + dos r

.a3> builtins.merge

.a3> add

structural type Rec = { uno : Nat, dos : Nat, tres : Text }

And checking that after updating this record, there's nothing todo:

.> fork a3 a4
.a4> update.old
.a4> todo