3.3 Use LispE in your C programs

LispE from a C++ program

In fact, it is possible to create and call a LispE interpreter from a C++ program. All you need to do is to link with the liblispe.a library created in the bin directory along with the executable.

The operation takes only a few lines of code:

#include "lispe.h"

//We create a LispE interpreter
LispE* lisp = new LispE;

// Loading and executing a LispE program
Element* e = lisp->load(filename);

//The result is displayed
cout << e->toString(lisp) << endl;

//We get rid of the object
e->release();

delete lisp;

If you have the code in the form of a string, it is also possible to use:

Element* e = lisp->execute("(cons 'a ())");
//The result is displayed
cout << e->toString(lisp) << endl;
//We get rid of the object
e->release();

Note the use of toString, which returns a std::string object that can be displayed on screen. The internal Unicode std::wstring are then converted into UTF8 strings on the fly.

For example, here is the simplest LispE interpreter you can create:

int main(int argc, char *argv[]) {
    LispE lisp;

    //loading a file and executing it
    if (argc == 2) {
        string file = argv[1];
        Element* e = lisp.load(file);
        std::cout << e->toString(&lisp) << std::endl;
        e->release();
        return 0;
    }

    string code;
    //keyboard reading of a LispE expression and evaluation on the fly
    cout << endl < "Lisp Elementary (" << version << ")" << endl << endl;
    std::cout << "> ";
    while (getline(std::cin, code)) {
        s_trim(code);
        //if it's not a LispE expression, we create a call to 'print'; //if it's not a LispE expression, we create a call to 'print'.
        //In this way, you can display the content of a variable
        if (code [0] != '(' && code.back() != ')') {
            code = "(print" + code + ")";
        }
        Element* e = lisp.execute(code);
        std::cout << e->toString(&lisp) << std::endl;
        e->release();
        code = "";
        std::cout << "> ";
    }
}