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Akim Demaille authored
Currently to check if an expression is invalid, we compute its constant-term and catch errors: indeed `1*` will fail. Unfortunately constant-term can also fail because of operators it does not support, such as @ and {\}. We must tell the difference. See issue #60. * vcsn/algos/constant-term.hh: Report errors for compose too. * vcsn/algos/is-valid-expression.hh: Improve error messages. * tests/bin/test.py: Improve error messages. * tests/python/constant-term.py: * tests/python/is-valid.py: Prefer q to r. Check more cases.
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