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A non-function coerced to a function can cause a stg_ap_v_ret

    • Closed Issue created by WheatWizard @trac-WheatWizard

    If you create an function by unsafe coercing a non-function you can get some strange functions. If you then take one of these function and apply it something it crashes with a stg_ap_v_ret. Here is a pretty minimal example.

    import Unsafe.Coerce
main=(unsafeCoerce()::a->IO())1

    You can reproduce it online here: https://tio.run/##y0gszk7Nyfn/PzO3IL@oRCE0rzgxLVXPOT@1KDmVKzcxM89WoxQsBhHS0LSyStS18/TX0NQ0/P8fAA

    Here is another one:

    import Unsafe.Coerce
g=unsafeCoerce()::a->a
main=print$g(g)1

    If you coerce functions this doesn't appear to happen.

    For example:

    import Unsafe.Coerce
main=(unsafeCoerce id::a->IO())1

    is a fine program. Sometimes this causes a segmentation fault (particularly with higher airity functions):

    import Unsafe.Coerce
main=(unsafeCoerce(+)::a->IO())1

    but I've never gotten it to make a stg_ap_v_ret.

    Edited
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