CPM.cmake/test/test.cpp

#include <lars/parser_generator.h>

int main() {
  lars::ParserGenerator<float> g;

  // Define grammar and evaluation rules
  g.setSeparator(g["Whitespace"] << "[\t ]");
  g["Sum"     ] << "Add | Subtract | Product";
  g["Product" ] << "Multiply | Divide | Atomic";
  g["Atomic"  ] << "Number | '(' Sum ')'";
  g["Add"     ] << "Sum '+' Product"    >> [](auto e){ return e[0].evaluate() + e[1].evaluate(); };
  g["Subtract"] << "Sum '-' Product"    >> [](auto e){ return e[0].evaluate() - e[1].evaluate(); };
  g["Multiply"] << "Product '*' Atomic" >> [](auto e){ return e[0].evaluate() * e[1].evaluate(); };
  g["Divide"  ] << "Product '/' Atomic" >> [](auto e){ return e[0].evaluate() / e[1].evaluate(); };
  g["Number"  ] << "'-'? [0-9]+ ('.' [0-9]+)?" >> [](auto e){ return stof(e.string()); };
  g.setStart(g["Sum"]);

  // Execute a string
  float result = g.run("1 + 2 * (3+4)/2 - 3");

  // validate result
  if (result == 5) {
    return 0;
  } else {
    return 1;
  }
}