T6123.hs:10:14:
    Occurs check: cannot construct the infinite type: a0 ~ Id a0
    The type variable ‛a0’ is ambiguous
    Relevant bindings include cundefined :: a0 (bound at T6123.hs:10:1)
    In the expression: cid undefined
    In an equation for ‛cundefined’: cundefined = cid undefined