Revise docs.

RELEASES.md

@@ -4,6 +4,8 @@ Rhai Release Notes
 Version 0.20.0
 ==============
 
+This version adds a variable resolver with the ability to short-circuit variable access.
+
 Breaking changes
 ----------------
 
@@ -17,6 +19,7 @@ Breaking changes
 * `rhai::ser` and `rhai::de` namespaces are merged into `rhai::serde`.
 * New reserved symbols: `++`, `--`, `..`, `...`.
 * Callback signature for custom syntax implementation function is changed to allow for more flexibility.
+* Default call stack depth for `debug` builds is reduced to 12 (from 16).
 
 New features
 ------------
@@ -24,15 +27,15 @@ New features
 * New `Engine::on_var` to register a _variable resolver_.
 * `const` statements can now take any expression (or none at all) instead of only constant values.
 * `OptimizationLevel::Simple` now eagerly evaluates built-in binary operators of primary types (if not overloaded).
-* Added `is_def_var()` to detect if variable is defined, and `is_def_fn()` to detect if script function is defined.
+* `is_def_var()` to detect if variable is defined, and `is_def_fn()` to detect if script function is defined.
 * `Dynamic::from(&str)` now constructs a `Dynamic` with a copy of the string as value.
 * `AST::combine` and `AST::combine_filtered` allows combining two `AST`'s without creating a new one.
+* `map`, `filter` and `reduce` functions for arrays.
 
 Enhancements
 ------------
 
 * Many one-liners and few-liners are now marked `#[inline]` or `[inline(always)]`, just in case it helps when LTO is not turned on.
-* Default call stack depth for `debug` builds is reduced to 12 (from 16).
 
 
 Version 0.19.0

doc/src/about/features.md

@@ -17,6 +17,8 @@ Easy
 * Very few additional dependencies - right now only [`smallvec`](https://crates.io/crates/smallvec/) plus crates for procedural macros;
   for [`no-std`] and `WASM` builds, a number of additional dependencies are pulled in to provide for missing functionalities.
 
+* [Plugins] system powered by procedural macros simplifies custom API development.
+
 Fast
 ----
 
@@ -41,6 +43,8 @@ Dynamic
 
 * Some support for [object-oriented programming (OOP)][OOP].
 
+* Hook into variables access via [variable resolver].
+
 Safe
 ----
 
@@ -66,9 +70,6 @@ Flexible
 
 * Supports [most build targets](targets.md) including `no-std` and [WASM].
 
-* [Plugins] system powered by procedural macros simplifies custom API development.
-
 * Surgically [disable keywords and operators] to restrict the language.
 
-* Use as a [DSL] by [disabling keywords/operators][disable keywords and operators], [custom operators]
+* Use as a [DSL] by defining [custom operators] and/or extending the language with [custom syntax].
-  and extending the language with [custom syntax].

doc/src/about/non-design.md

@@ -10,7 +10,7 @@ It doesn't attempt to be a new language. For example:
 
 * No traits...  so it is also not Rust. Do your Rusty stuff in Rust.
 
-* No structures/records - define your types in Rust instead; Rhai can seamlessly work with _any Rust type_.
+* No structures/records/tuples - define your types in Rust instead; Rhai can seamlessly work with _any Rust type_.
 
   There is, however, a built-in [object map] type which is adequate for most uses.
   It is possible to simulate [object-oriented programming (OOP)][OOP] by storing [function pointers]
@@ -32,7 +32,7 @@ It doesn't attempt to be a new language. For example:
   integrate with native Rust applications.
 
 * No formal language grammar - Rhai uses a hand-coded lexer, a hand-coded top-down recursive-descent parser
-  for statements and a Pratt parser for expressions.
+  for statements, and a hand-coded Pratt parser for expressions.
   
   This lack of formalism allows the parser itself to be exposed as a service in order to support
   [disabling keywords/operators][disable keywords and operators], adding [custom operators],
@@ -43,8 +43,8 @@ Do Not Write The Next 4D VR Game in Rhai
 ---------------------------------------
 
 Due to this intended usage, Rhai deliberately keeps the language simple and small by omitting
-advanced language features such as classes, inheritance, first-class functions, closures,
+advanced language features such as classes, inheritance, interfaces, generics,
-concurrency, byte-codes VM, JIT etc.
+first-class functions/closures, pattern matching, concurrency, byte-codes VM, JIT etc.
 
 Avoid the temptation to write full-fledge application logic entirely in Rhai -
 that use case is best fulfilled by more complete languages such as JavaScript or Lua.

doc/src/engine/var.md

@@ -10,7 +10,7 @@ searches the [`Scope`] that is passed into the `Engine::eval` call.
 There is a built-in facility for advanced users to _hook_ into the variable
 resolution service and to override its default behavior.
 
-To do so, provide a closure to the [`Engine`] via the [`Engine::on_var`] method:
+To do so, provide a closure to the [`Engine`] via the `Engine::on_var` method:
 
 ```rust
 let mut engine = Engine::new();
@@ -45,6 +45,18 @@ a variable resolver. Then these variables can be assigned to and their updated v
 the script is evaluated.
 
 
+Benefits of Using a Variable Resolver
+------------------------------------
+
+1. Avoid having to maintain a custom [`Scope`] with all variables regardless of need (because a script may not use them all).
+
+2. _Short-circuit_ variable access, essentially overriding standard behavior.
+
+3. _Lazy-load_ variables when they are accessed, not up-front. This benefits when the number of variables is very large, when they are timing-dependent, or when they are expensive to load.
+
+4. Rename system variables on a script-by-script basis without having to construct different [`Scope`]'s.
+
+
 Function Signature
 ------------------
 
@@ -68,5 +80,13 @@ where:
   * `context.namespace(): &Module` - reference to the current _global namespace_ (as a [module]) containing all script-defined functions.
   * `context.call_level(): usize` - the current nesting level of function calls.
 
-The return value is `Result<Option<Dynamic>, Box<EvalAltResult>>` where `Ok(None)` indicates that the normal
+### Return Value
-variable resolution process should continue.
+
+The return value is `Result<Option<Dynamic>, Box<EvalAltResult>>` where:
+
+* `Ok(None)` - normal variable resolution process should continue, meaning to continue searching through the [`Scope`].
+
+* `Ok(Some(Dynamic))` - wrapped [`Dynamic`] is taken as the value of the variable, which is treated as a constant.
+
+* `Err(Box<EvalAltResult>)` - error is reflected back to the [`Engine`].
+  Normally this is `EvalAltResult::ErrorVariableNotFound` to indicate that the variable does not exist, but it can be any error.

doc/src/language/arrays.md

@@ -40,7 +40,7 @@ The following methods (mostly defined in the [`BasicArrayPackage`][packages] but
 | `insert`                  | 1) element to insert<br/>2) position (beginning if <= 0, end if >= length)      | inserts an element at a certain index                                                                                                                                                                             |
 | `pop`                     | _none_                                                                          | removes the last element and returns it ([`()`] if empty)                                                                                                                                                         |
 | `shift`                   | _none_                                                                          | removes the first element and returns it ([`()`] if empty)                                                                                                                                                        |
-| `remove`                  | index                                                                           | removes an element at a particular index and returns it, or returns [`()`] if the index is not valid                                                                                                              |
+| `remove`                  | index                                                                           | removes an element at a particular index and returns it ([`()`] if the index is not valid)                                                                                                                        |
 | `reverse`                 | _none_                                                                          | reverses the array                                                                                                                                                                                                |
 | `len` method and property | _none_                                                                          | returns the number of elements                                                                                                                                                                                    |
 | `pad`                     | 1) target length<br/>2) element to pad                                          | pads the array with an element to at least a specified length                                                                                                                                                     |

doc/src/patterns/dynamic-const.md

@@ -35,8 +35,8 @@ Implementation
 let mut engine = Engine::new();
 
 // Create shared data provider.
-// Assume that Provider::get(&str) -> Option<value> gets a system constant.
+// Assume that SystemValuesProvider::get(&str) -> Option<value> gets a value.
-let provider: Arc<Provider> = get_data_provider();
+let provider = Arc::new(SystemValuesProvider::new());
 
 // Clone the shared provider
 let db = provider.clone();