Topic: String formula evaluator

[Keith™]

I am looking for advice on a string formula evaluator, ideally the formula would be sent to the evaluator and it would return an object that could be cast into a numeric type.


I am currently working with Flee but it only does the basic stuff. I need ROUND, ABS, MIN, MAX, etc. and it doesn't work well with the new project.

[MickD]

There's no easy way to do this unless you build a simple interpreter. The hardest part is parsing and lexing but as you may only need a small subset of a real language it will be a lot easier.

http://www.craftinginterpreters.com/

The link above is excellent and even just reading through part 1 (the Java interpreter) will give you more than enough info to get something going or at least some direction or a better understanding of Flee.

I've built the Java version and about to start the C version, my interest is in building a small scripting language to automate my plugins. What you are doing is no different only you are parsing short sentences which will be a lot easier (in theory )

[Keith™]

Precisely why I am looking for an existing library.

Ideally the library would allow me to import functions that would be interpreted something like:

Code - C#: [Select]

1. Evaluator.functions.Add(foo);
2.  
3. function double foo(double value)
4. {
5.     //dostuff here
6. }

I'm having a little bit of difficulty right now .. just got home and I am pretty sure I have consumed nearly a whole 1.5L bottle so forgive me if my message is a little incoherent

[JohnK]

As far as the orig question goes, read the first two sections.

https://llvm.org/docs/tutorial/

Kaleidoscope: Implementing a Language with LLVM
1. Kaleidoscope: Tutorial Introduction and the Lexer
2. Kaleidoscope: Implementing a Parser and AST
...

Going to IR/L is a bit overkill for a simple parser like this (a whole mess more code).

Mick,
If you put that code up on github (or the like), let me know. That would be cool.

[Keith™]

Oh my ... and Saturday night was something else ... turns out I drank a whole 1.5L bottle of Captain Morgan.

Anyway, the reading assignment looks pretty cool. I'm sure its something I could work with. A week or two should give me enough time to have enough to do what I need, maybe even more

[MickD]

Oh my ... and Saturday night was something else ... turns out I drank a whole 1.5L bottle of Captain Morgan.

Anyway, the reading assignment looks pretty cool. I'm sure its something I could work with. A week or two should give me enough time to have enough to do what I need, maybe even more

It's a good read/study and well worth it I reckon. You will definitely be able to knock up something simple n C#

Mick,
If you put that code up on github (or the like), let me know. That would be cool.

Will do, the C section by the author is still in progress but is starting to get interesting - dynamic strings are next

[Keith™]

Fortunately for me, there is really only a small subset of mathematical functions that I need to implement and I will only need to evaluate two functions, although those two will need to be evaluated on average about 300 times each.