calc

Calculator

Contributed by Serghei Iakovlev, public domain.

This is a very simple calculator. To compile the program do the following:

$ make

Then, to run the example issue the following command:

./calc

Let's explain what is actually happening: Take a look at the file main.c, then, take a look at calc.c. The main.c file is appended to the raw form of calc.c in the Makefile. lemon does not create a complete program - only the necessary subroutines. So it is necessary to build in the main part of a program.

If you make your own changes to this example program, you should make the changes to calc.y or main.c. calc.c and calc.h are auto-generated files, and they will be over-written every time lemon is run.

Disecting main.c: These are the essential functions that must be called. Note, this is a stripped down simple version with no error checking or tokenizer. The tokens are hardwired in so we can see exactly how lemon operates.

void* pParser = ParseAlloc (malloc);

The next 4 lines parse the command 15 DIVIDE 5.

Parse (pParser, INTEGER, 15);
Parse (pParser, DIVIDE, 0);
Parse (pParser, INTEGER, 5);
Parse (pParser, 0, 0);

INTEGER and DIVIDE are assigned values in the generated file cacl.h to be the following;

#define PLUS    1
#define MINUS   2
#define DIVIDE  3
#define TIMES   4
#define INTEGER 5

Again, this is a generated file, so if any additions are made to this file, they'll be over-written when re-running lemon.