else if isPrimTyCon tycon {- array, we hope -} then 'A' -- Bogus
else if isEnumerationTyCon tycon then 'E'
else if isTupleTyCon tycon then 'T'
- else if isJust (maybeTyConSingleCon tycon) then 'S'
+ else if isJust (tyConSingleDataCon_maybe tycon) then 'S'
else if utc == listTyConKey then 'L'
else 'M' -- oh, well...