T10715b.hs:7:7: error:
    Occurs check: cannot construct the infinite type: b ~ [b]
      arising from a use of ‘coerce’
    In the first argument of ‘asTypeOf’, namely ‘coerce’
    In the expression: coerce `asTypeOf` head
    In an equation for ‘foo’: foo = coerce `asTypeOf` head
    Relevant bindings include foo :: [b] -> b (bound at T10715b.hs:7:1)