Morphir elm compiler does not enforce pattern match completeness

[edwardpeters]

Describe the bug
Morphir elm will compile code with incomplete pattern matching. This can result in runtime errors.

To Reproduce
The following code compiles:

type MyUnion = A | B

foo : MyUnion -> String
foo x = case x of
    A -> "A"

bar : Int -> String
bar i = foo B

When bar is run, it results in "Unable to compute", as makes sense given that the pattern match does not handle that case.

Expected behavior
Type checking should enforce that pattern matching is exhaustive.

Desktop (please complete the following information):

• OS: OSX
• Version: 2.89.0