Looking at the grammar at http://www.adahome.com/rm95/rm9x-P.html and http://www.adaic.org/resources/add_content/standards/05rm/html/RM-2-4.html I see the following restrictions apply: - A number must begin and end with a digit. There must be at least one digit on either side of each underscore and decimal point. - There may be at most one decimal point in a number. - The base must be between 2 and 16, inclusive. [-+]?( [0-9](_?[0-9])*([.][0-9](_?[0-9])*)?| ([2-9]|1[0-6])#[0-9a-fA-F](_?[0-9a-fA-F])*([.][0-9a-fA-F](_?[0-9a-fA-F])*)?# )([eE][+-]?[0-9](_?[0-9])*)? If you want a slightly smaller version, we can drop the "only one decimal point" rule and get [-+]?( [0-9]([._]?[0-9])*| ([2-9]|1[0-6])#[0-9a-fA-F]([._]?[0-9a-fA-F])*# )([eE][+-]?[0-9](_?[0-9])*)? Ideally, for a based number, the range of acceptable digits would depend on the base. Which is possible for a finite-state machine since the number of bases is finite, but laeds to a bit of a state explosion. Here's an approximation that separates bases 2-9 and 10-16: [-+]?( [0-9](_?[0-9])*([.][0-9](_?[0-9])*)?| [2-9]#[0-8](_?[0-8])*([.][0-8](_?[0-8])*)?#| 1[0-6]#[0-9a-fA-F](_?[0-9a-fA-F])*([.][0-9a-fA-F](_?[0-9a-fA-F])*)?# )([eE][+-]?[0-9](_?[0-9])*)? because I think that this is overdoing it: [-+]?( [0-9](_?[0-9])*([.][0-9](_?[0-9])*)?| 2#[0-1](_?[0-1])*([.][0-1](_?[0-1])*)?#| 3#[0-2](_?[0-2])*([.][0-2](_?[0-2])*)?#| 4#[0-3](_?[0-3])*([.][0-3](_?[0-3])*)?#| 5#[0-4](_?[0-4])*([.][0-4](_?[0-4])*)?#| 6#[0-5](_?[0-5])*([.][0-5](_?[0-5])*)?#| 7#[0-5](_?[0-5])*([.][0-5](_?[0-5])*)?#| 8#[0-7](_?[0-7])*([.][0-7](_?[0-7])*)?#| 9#[0-8](_?[0-8])*([.][0-8](_?[0-8])*)?#| 10#[0-9](_?[0-9])*([.][0-9](_?[0-9])*)?#| 11#[0-9aA](_?[0-9aA])*([.][0-9aA](_?[0-9aA])*)?#| 12#[0-9abAB](_?[0-9abAB])*([.][0-9abAB](_?[0-9abAB])*)?#| 13#[0-9a-cA-C](_?[0-9a-cA-C])*([.][0-9a-cA-C](_?[0-9a-cA-C])*)?#| 14#[0-9a-dA-D](_?[0-9a-dA-D])*([.][0-9a-dA-D](_?[0-9a-dA-D])*)?#| 15#[0-9a-eA-E](_?[0-9a-eA-E])*([.][0-9a-eA-E](_?[0-9a-eA-E])*)?#| 16#[0-9a-fA-F](_?[0-9a-fA-F])*([.][0-9a-fA-F](_?[0-9a-fA-F])*)?#| )([eE][+-]?[0-9](_?[0-9])*)? Another point is that Ada doesn't actually include leading + or - signs in the syntax for "number", but rather makes them unary operators. This means that spaces are allowed, and whether you want to include them in the "number" pattern is a judgement call. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html