examples/extern_methods: revamp as a better teaching example

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/examples/extern_methods.nit b/examples/extern_methods.nit
index 333540b..c91cdb7 100644 (file)
--- a/examples/extern_methods.nit
+++ b/examples/extern_methods.nit
@@ -14,13 +14,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# This module illustrates some uses of the FFI, specifically
-# how to use extern methods. Which means to implement a Nit method in C.
+# Sample program using extern methods implemented in C and other FFI services
 module extern_methods
 
 redef enum Int
-       # Returns self'th fibonnaci number
-       # implemented here in C for optimization purposes
+       # Get the `self`th Fibonacci number
+       #
+       # The FFI can be used to optimize performance critical methods.
+       # Although this implementation is recursive, so there is not much gain.
+       # Notice the `import fib` telling the compiler that there is a callback to `foo` from the C code.
+       # From C, `foo` is called through the function `Int_fib` with the receiver as argument.
        fun fib: Int import fib `{
                if (self < 2)
                        return self;
@@ -28,22 +31,27 @@ redef enum Int
                        return Int_fib(self-1) + Int_fib(self-2);
        `}
 
-       # System call to sleep for "self" seconds
+       # System call to sleep for `self` seconds
+       #
+       # You can use the FFI to access any system functions, sometimes it's extremely simple.
        fun sleep `{
                sleep(self);
        `}
 
-       # Return atan2l(self, x) from libmath
-       fun atan_with(x: Int): Float `{
-               return atan2(self, x);
-       `}
-
-       # This method callback to Nit methods from C code
-       # It will use from C code:
-       # * the local fib method
-       # * the + operator, a method of Int
-       # * to_s, a method of all objects
-       # * String.to_cstring, a method of String to return an equivalent char*
+       # Print the result of adding `self` to `self.fib` with callbacks from C
+       #
+       # This method illustrates many forms of callbacks from C,
+       # but it would have been better implemented in Nit (as done by `bar`).
+       #
+       # It is recommended to avoid callbacks when possible, use each language according to their strengths.
+       # Nit is better than C to call methods and manipulate objects.
+       # C has easy access to system functions, native libraries and it does low-level stuff.
+       #
+       # The implementation calls:
+       # * the local `fib` method,
+       # * the `+` operator, a method of `Int`,
+       # * `to_s`, a method of all objects,
+       # * `String.to_cstring`, a method of `String` to get as a `char*`.
        fun foo import fib, +, to_s, String.to_cstring `{
                long self_fib = Int_fib(self);
                long self_plus_fib = Int__plus(self, self_fib);
@@ -54,16 +62,25 @@ redef enum Int
                printf("from C: self + fib(self) = %s\n", c_string);
        `}
 
-       # Equivalent to foo but written in pure Nit
+       # Equivalent to `foo` but written in pure Nit
        fun bar do print "from Nit: self + fib(self) = {self+self.fib}"
 end
 
+redef class Float
+       # Arctangent of `self` and `other` using `atan2` from `math.h`
+       #
+       # Universal types (Int, Float, Bool, etc.) are converted to their closest equivalent in C
+       # (long, double, int, etc.).
+       fun atan_with(other: Float): Float `{
+               return atan2(self, other);
+       `}
+end
+
 print 12.fib
 
 print "sleeping 1 second..."
 1.sleep
 
-print 100.atan_with(200)
+print 100.0.atan_with(200.0)
 8.foo
 8.bar
-