do loop.

doc/src/SUMMARY.md

@@ -79,6 +79,7 @@ The Rhai Scripting Language
    9. [If Statement](language/if.md)
    10. [Switch Expression](language/switch.md)
    11. [While Loop](language/while.md)
+   11. [Do Loop](language/do.md)
    12. [Loop Statement](language/loop.md)
    13. [For Loop](language/for.md)
    14. [Return Values](language/return.md)

doc/src/appendix/keywords.md

@@ -14,7 +14,9 @@ Keywords List
 |         `if`          | if statement                                |                 |      no      |              |
 |        `else`         | else block of if statement                  |                 |      no      |              |
 |       `switch`        | matching                                    |                 |      no      |              |
-|        `while`        | while loop                                  |                 |      no      |              |
+|         `do`          | looping                                     |                 |      no      |              |
+|        `while`        | 1) while loop<br/>2) condition for do loop  |                 |      no      |              |
+|        `until`        | do loop                                     |                 |      no      |              |
 |        `loop`         | infinite loop                               |                 |      no      |              |
 |         `for`         | for loop                                    |                 |      no      |              |
 |         `in`          | 1) containment test<br/>2) part of for loop |                 |      no      |              |
@@ -48,11 +50,11 @@ Reserved Keywords
 | `var`     | variable declaration  |
 | `static`  | variable declaration  |
 | `shared`  | share value           |
-| `do`      | looping               |
 | `each`    | looping               |
 | `then`    | control flow          |
 | `goto`    | control flow          |
 | `exit`    | control flow          |
+| `unless`  | control flow          |
 | `match`   | matching              |
 | `case`    | matching              |
 | `public`  | function/field access |

doc/src/language/do.md

@@ -0,0 +1,28 @@
+`do` Loop
+=========
+
+{{#include ../links.md}}
+
+`do` loops have two opposite variants: `do` ... `while` and `do` ... `until`.
+
+Like the `while` loop, `continue` can be used to skip to the next iteration, by-passing all following statements;
+`break` can be used to break out of the loop unconditionally.
+
+```rust
+let x = 10;
+
+do {
+    x -= 1;
+    if x < 6 { continue; }  // skip to the next iteration
+    print(x);
+    if x == 5 { break; }    // break out of do loop
+} while x > 0;
+
+
+do {
+    x -= 1;
+    if x < 6 { continue; }  // skip to the next iteration
+    print(x);
+    if x == 5 { break; }    // break out of do loop
+} until x == 0;
+```