Fix type-checking bugs in let
#136
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Dhall requires that a `let` expression of the form: ```haskell let x : t = e1 in e2 ``` ... should behave the same as the following equivalent lambda expression: ```haskell (λ(x : t) → e2) e1 ``` ... meaning that if one type-checks then the other should type-check and (vice versa) if one does not type-check then the other should not type-check. The only difference should be either: * the error message changes (i.e. to be more `let`-specific) * the order in which errors are checked might differ I used equational reasoning to discover two corner cases where the two expressions diverged in their type-checking behavior. This change fixes that and includes two regression tests to capture the two corner cases to prevent this problem from recurring
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Fixes #135
Dhall requires that a
letexpression of the form:... should behave the same as the following equivalent lambda expression:
... meaning that if one type-checks then the other should type-check and (vice
versa) if one does not type-check then the other should not type-check. The
only difference should be either:
let-specific)I used equational reasoning to discover two corner cases where the two
expressions diverged in their type-checking behavior. This change fixes that
and includes two regression tests to capture the two corner cases to prevent
this problem from recurring