Add currying support.

doc/src/SUMMARY.md

@@ -76,6 +76,7 @@ The Rhai Scripting Language
        3. [Namespaces](language/fn-namespaces.md)
        4. [Function Pointers](language/fn-ptr.md)
        5. [Anonymous Functions](language/fn-anon.md)
+       6. [Currying](language/fn-curry.md)
    15. [Print and Debug](language/print-debug.md)
    16. [Modules](language/modules/index.md)
        1. [Export Variables, Functions and Sub-Modules](language/modules/export.md)

doc/src/appendix/keywords.md

@@ -26,6 +26,7 @@ Keywords List
 | `fn` (lower-case `f`) | Function definition                      |   [`no_function`]   |
 |  `Fn` (capital `F`)   | Function to create a [function pointer]  |                     |
 |        `call`         | Call a [function pointer]                |                     |
+|        `curry`        | Curry a [function pointer]               |                     |
 |        `this`         | Reference to base object for method call |   [`no_function`]   |
 |       `type_of`       | Get type name of value                   |                     |
 |        `print`        | Print value                              |                     |

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
+```

doc/src/links.md

@@ -76,6 +76,7 @@
 [functions]: {{rootUrl}}/language/functions.md
 [function pointer]: {{rootUrl}}/language/fn-ptr.md
 [function pointers]: {{rootUrl}}/language/fn-ptr.md
+[currying]: {{rootUrl}}/language/fn-curry.md
 [function namespace]: {{rootUrl}}/language/fn-namespaces.md
 [function namespaces]: {{rootUrl}}/language/fn-namespaces.md
 [anonymous function]: {{rootUrl}}/language/fn-anon.md