Added additional example and info.

Makefile

@@ -3,7 +3,7 @@ CCFLAGS = -ansi -Wall -Wshadow -O2
 LFLAGS = -lm
 
 
-all: test bench example example2
+all: test bench example example2 example3
 
 
 test: test.o tinyexpr.o
@@ -20,6 +20,9 @@ example: example.o tinyexpr.o
 example2: example2.o tinyexpr.o
 	$(CC) $(CCFLAGS) -o $@ $^ $(LFLAGS)
 
+example3: example3.o tinyexpr.o
+	$(CC) $(CCFLAGS) -o $@ $^ $(LFLAGS)
+
 .c.o:
 	$(CC) -c $(CCFLAGS) $< -o $@
 

README.md

@@ -15,6 +15,7 @@ the standard C math functions and runtime binding of variables.
 - Simple and fast.
 - Implements standard operators precedence.
 - Exposes standard C math functions (sin, sqrt, ln, etc.).
+- Can add custom functions and variables easily.
 - Can bind variables at eval-time.
 - Released under the zlib license - free for nearly any use.
 - Easy to use and integrate with your code
@@ -168,6 +169,23 @@ This produces the output:
                 5.000000
 
 
+##Binding to Custom Functions
+
+TinyExpr can also call to custom functions implemented in C. Here is a short example:
+
+```C
+double my_sum(double a, double b) {
+    /* Example C function that adds two numbers together. */
+    return a + b;
+}
+
+te_variable vars[] = {
+    {"mysum", my_sum, TE_FUNCTION2} /* TE_FUNCTION2 used because my_sum takes two arguments. */
+};
+
+te_expr *n = te_compile("mysum(5, 6)", vars, 1, 0);
+
+```
 
 
 ##How it works
@@ -219,7 +237,12 @@ TinyExpr parses the following grammar:
     <term>      =    <factor> {("*" | "/" | "%") <factor>}
     <factor>    =    <power> {"^" <power>}
     <power>     =    {("-" | "+")} <base>
-    <base>      =    <constant> | <variable> | <function-0> {"(" ")"} | <function-1> <power> | <function-2> "(" <expr> "," <expr> ")" | "(" <list> ")"
+    <base>      =    <constant>
+                   | <variable>
+                   | <function-0> {"(" ")"}
+                   | <function-1> <power>
+                   | <function-X> "(" <expr> {"," <expr>} ")"
+                   | "(" <list> ")"
 
 In addition, whitespace between tokens is ignored.
 

example3.c

@@ -0,0 +1,35 @@
+#include "tinyexpr.h"
+#include <stdio.h>
+
+
+/* An example of calling a C function. */
+double my_sum(double a, double b) {
+    printf("Called C function with %f and %f.\n", a, b);
+    return a + b;
+}
+
+
+int main(int argc, char *argv[])
+{
+    te_variable vars[] = {
+        {"mysum", my_sum, TE_FUNCTION2}
+    };
+
+    const char *expression = "mysum(5, 6)";
+    printf("Evaluating:\n\t%s\n", expression);
+
+    int err;
+    te_expr *n = te_compile(expression, vars, 1, &err);
+
+    if (n) {
+        const double r = te_eval(n);
+        printf("Result:\n\t%f\n", r);
+        te_free(n);
+    } else {
+        /* Show the user where the error is at. */
+        printf("\t%*s^\nError near here", err-1, "");
+    }
+
+
+    return 0;
+}

test.c

@@ -495,6 +495,7 @@ void test_optimize() {
         {"5+5", 10},
         {"pow(2,2)", 4},
         {"sqrt 100", 10},
+        {"pi * 2", 6.2832},
     };
 
     int i;