Execute String
Blitz3D Forums/Blitz3D Programming/Execute String
| ||
| If there is already a topic on this, I couldn't seem to find it. Is there any way that I could store an expression in a string, and be able to execute it? I am using finite state machines to control the AI's in my game, and I need to store conditions in an array, so when it comes time to do checks, I can just go through each entry in the string array and evaluate the strings. Is this possible? Or is there a better way of doing what I'm trying to do? Thanks! |
| ||
| In that case, using a Select..Case might be the most suitable solution. But there are several solutions for this. I searched for eval site:blitzbasic.com to find this archive entry: http://www.blitzmax.com/codearcs/codearcs.php?code=407 |
| ||
| I think I'll stick to Selects, because it's not worth the work to evaluate strings like that. Plus, by using a Select, I have more flexibility and control over my states. |
| ||
| If you want to just evaluate a string expression there are many posts in the code archives about it, but all of them are broken in some way. Here is another one i put together
Function Eval#(sExp$,lExp$="",n#=0,op$="+")
Local m_next$
Local m#
Print lexp
If Len(sExp) Then
lExp = sExp.Replace(" ","") + ")"
EndIf
While op <> ")"
m_next = pop(lexp)
Print lexp
If m_next = "(" Then
m_next = eval("",lexp)
Else
While "+-*/)".find(Chr(lexp[0])) = -1
m_next :+ pop(lexp)
Wend
EndIf
m = Float(m_next)
Select op
Case "+" n=n+m
Case "-" n=n-m
Case "*" n=n*m
Case "/" n=n/m'(m Or 1.0)
Default RuntimeError("!!!")
EndSelect
op = pop(lexp)
Wend
Return n
End Function
Function pop$(s$ Var)
Local tmp$ = Chr(s[0])
s = Right(s,s.length-1)
Return tmp
End Function
Print eval("190/-2")
It sounds more like you need a scripting language. Do a forum search for: BVM MicroC LugI . |
| ||
| It sounds like your situation might be a pretty good match for this library I posted a while back: http://www.blitzbasic.com/Community/posts.php?topic=92323 It accepts strings containing code written in the C programming language, and compiles them at runtime to machine code in memory. The result runs about as fast as compiled B3D code, so it's a lot faster than scripting engines or anything like that. C is obviously a very different language from B3D overall, but simple expressions and function calls are going to be pretty much the same between the two (just remember that ending semicolon). You could write a wrapper function that packages your domain-specific expression language with a pre-written framework function so that you don't have to defile your game logic with anything that looks like C. You could also do a search for scripting languages, as one of those would also do what you want. However, interpreted bytecode is slow and, to be brutally honest, none of the currently available B3D scripting libraries are very good. |
   |