function returns an expr when expr is applied as its argument
if a function takes exprs as its arguments, it returns expr object.
>>> func(a, b, c) = {} >>> func(`x, 1, 2) `func(x, 1, 2)
This implementation would make some confliction in the existing specification.
if a function takes exprs as its arguments, it returns expr object.
>>> func(a, b, c) = {} >>> func(`x, 1, 2) `func(x, 1, 2)