Herbert
In tests/monadfail/MonadFailErrors.stderr I see
MonadFailErrors.hs:59:5: error:
No instance for (MonadFail Identity)
arising from a do statement
with the failable pattern ‘Newtype x’
In a stmt of a 'do' block: Newtype x <- undefined
In the expression:
do { Newtype x <- undefined;
undefined }
In an equation for ‘newtypeMatch’:
newtypeMatch
= do { Newtype x <- undefined;
undefined }
MonadFailErrors.hs:67:5: error:
No instance for (MonadFail Identity)
arising from a do statement
with the failable pattern ‘Data x’
In a stmt of a 'do' block: Data x <- undefined
In the expression:
do { Data x <- undefined;
undefined }
In an equation for ‘singleConMatch’:
singleConMatch
= do { Data x <- undefined;
undefined }
But ‘Newtype’ and ‘Data’ are single constructor types and hence cannot fail.
So why are these errors happening?
I’m tiding up your implementation (deleting code!) and accidentally fixed this.
So I wanted to check that it is indeed wrong as-is.
Simon
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