Expression eval

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Function Syntax

float expression_eval(string expression )

  • expression is a mathematical expression to be solved.

Evaluates an expression using only the base components of the evaluator:

  • No spaces are allowed within the expression, except as part of a zone/location name.
  • + - * / ( ) have their usual mathematical meaning and precedence.
  • ^ is exponentiation, with the highest precedence.
  • Functions available: ceil(x) floor(x) sqrt(x) min(x,y) max(x,y)
  • Preferences function: pref(text)
    • This must be used on preferences with a float value ONLY - merely retrieving an integer pref will corrupt it!
  • There could be at most one of each text function in an expression.
    • This is no longer the case however and multiple of the same text functions should now work properly.
  • This wrapper allows user-defined variables to be used as well, which must have names starting with a lower-case letter (or underscore) to distinguish them from built-in variables. Variables are supplied as a float[string] map.


Code Sample

This script expands expression_eval() to include support for user-defined variables. It is extremely complex, but it is extremely useful to anyone who wants to use expression_eval().

float eval(string expr, float[string] vars) {
   buffer b;
   matcher m = create_matcher( "\\b[a-z_][a-zA-Z0-9_]*\\b", expr );
   while (m.find()) {
      string var =;
      if (vars contains var) {
         m.append_replacement(b, vars[var].to_string());
      // could implement functions, pref access, etc. here
   return expression_eval(b.to_string());

# Everything below this line shows how to make use of eval().

float[string] v;
v["pi"] = 3.14159265;
v["ten"] = 10;
print(eval("2+3", v));
print(eval("max(pi^ten,ten^pi)", v));
print(eval("sqrt(pi)*L", v));
print(eval("undefined/2", v));