kauboy26/evaluator

Evaluates a series of statements such as "a = 9 + (3 + 4) * 2, b = a + b", etc.

Evaluator

Other

Please check out PyEvaluator. It has functionality far exceeding that of this project and the parser and lexer were written by hand, in Python (i.e. without lex or yacc).

About

This thing evaluates assignment statements. To clarify further, here's an example (taken straight from the file "sample.txt"):

a = 15 + 1 * 5  
b = a * 2  
c = 19 + 1 + b + a  
9 * 9
c * 2
7
a

After the first statement is executed, the value of the expression on the right is stored into "a". Effectively, a = 20. In the next statement, b = a * 2 = 15 * 2 = 30.

You can also feed in expressions that don't assign any value to a variable, such as "9 * 9" (the console will print "81"), "c * 2" (in this case, 80), etc.

Usage

You need bison, the parser-generator, installed. Run (in the directory containing the file runscript.sh)

./runscript

to produce the parser generator and also run the executable. Alternatively, you can copy paste the commands contained within the file runscript.sh into your terminal.

To run the executable once it has been built, simply run

./madudes

You can type whatever you want into stdin. You can feed the sample file in with

cat sample.txt | ./madudes

Restrictions

Only use single character, lower-case variable names. Therefore, you can have at most 26 variables.

More info

I followed the GNU Bison documentation to make a calculator that evaluates expressions like "9 * 4 + 3", etc. That documentation is simply beautiful, it's extremely well done. I highly recommend reading it instead of following other tutorials online.

Anyhow, I modified that basic application to allow the use of variables. Since this was my first time with this Bison, it took a good deal of figuring out to make it work.