Minor fix to dhall diff
#1006
Merged
Minor fix to dhall diff
#1006
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`dhall diff` slightly misbehaves when diffing the following expression with
itself:
```dhall
λ(f : List Bool -> Bool) → f ([] : List Bool)
```
... producing the following diff:
```
λ(… : …
→ …)
→ …@…
- [ … ] : List …
+ [ … ] : List …
```
This is because there are two places in the `Dhall.Diff` module responsible
for comparing lists:
* Once in `diffApplicationExpression`, which compares two lists with at least
one type annotation between them
* Once in `diffPrimitiveExpression`, which compares two lists if neither one has
a type annotation
Those cases exhaustively cover all possible pairs of lists, but there was a
third (incorrect) fallback case that prematurely gave up and displayed them as
different. This fallback would trigger when applying a function to an empty
list, since the diffing algorithm wouldn't have a chance to return back to the
top-level `diffExpression` and try to compare the lists correctly in
`diffApplicationExpression`.
After this change, the diff now doesn't include a spurious difference:
```
λ(… : …
→ …)
→ …@…
…
```
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dhall diffslightly misbehaves when diffing the following expression withitself:
... producing the following diff:
This is because there are two places in the
Dhall.Diffmodule responsiblefor comparing lists:
diffApplicationExpression, which compares two lists with at leastone type annotation between them
diffPrimitiveExpression, which compares two lists if neither one hasa type annotation
Those cases exhaustively cover all possible pairs of lists, but there was a
third (incorrect) fallback case that prematurely gave up and displayed them as
different. This fallback would trigger when applying a function to an empty
list, since the diffing algorithm wouldn't have a chance to return back to the
top-level
diffExpressionand try to compare the lists correctly indiffApplicationExpression.After this change, the diff now doesn't include a spurious difference: