Add currying support.

doc/src/language/fn-curry.md

@@ -0,0 +1,30 @@
+Function Pointer Currying
+========================
+
+{{#include ../links.md}}
+
+It is possible to _curry_ a [function pointer] by providing partial (or all) arguments.
+
+Currying is done via the `curry` keyword and produces a new [function pointer] which carries
+the curried arguments.
+
+When the curried [function pointer] is called, the curried arguments are inserted starting from the left.
+The actual call arguments should be reduced by the number of curried arguments.
+
+```rust
+fn mul(x, y) {                  // function with two parameters
+    x * y
+}
+
+let func = Fn("mul");
+
+func.call(21, 2) == 42;         // two arguments are required for 'mul'
+
+let curried = func.curry(21);   // currying produces a new function pointer which
+                                // carries 21 as the first argument
+
+let curried = curry(func, 21);  // function-call style also works
+
+curried.call(2) == 42;          // <- de-sugars to 'func.call(21, 2)'
+                                //    only one argument is now required
+```