How can I evaluate a string containing a binary formula in Delphi?

Question

In Delphi XE I have a routine that breaks down some complicated formulas to a binary formula result like this:

(1&((1|0)|1)&1)

Since my application is on SQL Server I can easily do a SELECT (1&((1|0)|1)&1) As Result and SQL Server will evaluate the logic to give me a 1 or 0 result.

I cannot seem to find a native Delphi way of taking a string representation of a binary formula and evaluating it.

I looked into the Live Bindings Evaluators added to XE but any attempt at the and/or operators throws parser errors so I believe that to be more of a mathematical process.

I also looked at a few parsers but none really seemed to jump out at me.

So how can I do something similar to:

iSomeInt := Evaluate('(1&((1|0)|1)&1)');

BTW.. I can totally rework the formula and use and/or instead of &|.. that was just to make it work with SQL Server.

JCL TEvaluator looks good. refer to this previous SO question stackoverflow.com/questions/13592136/… — Sam
– Sam, Commented Aug 15, 2013 at 3:39
JCL expression evaluator is indeed good. Although it handles decimal separators badly, and lacks a power operator. Both of these omissions I have fixed in my own branch, but can I persuade any of the JEDI devs to do the necessary? Can I heck! Frustrating when open source projects die. And there seems no obvious way to bring it back to life. — David Heffernan
– David Heffernan, Commented Aug 15, 2013 at 6:17

Mason Wheeler · Accepted Answer · 2013-08-14 19:14:34Z

1

The problem isn't that it's "a mathematical process" so much as that the LiveBindings parser expects your mathematical process to be expressed with Pascal operators, but & and | are C operators.

Try something like this, assuming you have a function called LiveBindingsEval which evaluates a string with the LiveBindings parser:

function PreprocessExpression(const expr: string): string;
begin
   result := StringReplace(expr, '|', ' or ', [rfReplaceAll]);
   result := StringReplace(result, '&', ' and ', [rfReplaceAll]);
end;

iSomeInt := LiveBindingsEval(PreprocessExpression('(1&((1|0)|1)&1)'));

You may need to improve on this a little, but this should be enough to get you started on the right path...

answered Aug 14, 2013 at 19:14

Mason Wheeler

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1 Comment

digital alchemist Over a year ago

Mason ... I actually used the Delphi and or with the Evaluator and it didn't care for the operators at all.. it wasn't really obvious but I mentioned I was only using the & and | for SQL Server compatibility.I'll go back and give it another shot though.

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