More documentation on chained assignment.

scripts/primes.rhai

@@ -5,8 +5,7 @@ const MAX_NUMBER_TO_CHECK = 10000;    // 1229 primes
 let prime_mask = [];
 prime_mask.pad(MAX_NUMBER_TO_CHECK, true);
 
-prime_mask[0] = false;
+prime_mask[0] = prime_mask[1] = false;
-prime_mask[1] = false;
 
 let total_primes_found = 0;
 

src/lib.rs

@@ -80,7 +80,7 @@ pub use error::{ParseError, ParseErrorType};
 pub use fn_register::{RegisterDynamicFn, RegisterFn, RegisterResultFn};
 pub use parser::{Position, AST, FLOAT, INT};
 pub use result::EvalAltResult;
-pub use scope::Scope;
+pub use scope::{Scope, ScopeEntry, VariableType};
 
 #[cfg(not(feature = "no_index"))]
 pub use engine::Array;

src/parser.rs

@@ -153,12 +153,12 @@ impl AST {
     /// Optimize the AST with constants defined in an external Scope.
     ///
     /// Although optimization is performed by default during compilation, sometimes it is necessary to
-    /// "re"-optimize an AST. For example, when working with constants that are passed in via an
+    /// _re_-optimize an AST. For example, when working with constants that are passed in via an
     /// external scope, it will be more efficient to optimize the AST once again to take advantage
     /// of the new constants.
     ///
     /// With this method, it is no longer necessary to regenerate a large script with hard-coded
-    /// constant values. The script AST can be compiled once and stored. During actually evaluation,
+    /// constant values. The script AST can be compiled just once. During actual evaluation,
     /// constants are passed into the Engine via an external scope (i.e. with `scope.push_constant(...)`).
     /// Then, the AST is cloned and the copy re-optimized before running.
     pub fn optimize(self, scope: &Scope) -> Self {

src/scope.rs

@@ -8,21 +8,29 @@ use crate::parser::FLOAT;
 
 use std::borrow::Cow;
 
+/// Type of a variable in the Scope.
 #[derive(Debug, Eq, PartialEq, Hash, Copy, Clone)]
 pub enum VariableType {
+    /// Normal variable.
     Normal,
+    /// Immutable constant value.
     Constant,
 }
 
+/// An entry in the Scope.
 pub struct ScopeEntry<'a> {
+    /// Name of the variable.
     pub name: Cow<'a, str>,
+    /// Type of the variable.
     pub var_type: VariableType,
+    /// Current value of the variable.
     pub value: Dynamic,
+    /// A constant expression if the initial value matches one of the recognized types.
     pub expr: Option<Expr>,
 }
 
-/// A type containing information about current scope.
+/// A type containing information about the current scope.
-/// Useful for keeping state between `Engine` runs.
+/// Useful for keeping state between `Engine` evaluation runs.
 ///
 /// # Example
 ///
@@ -76,6 +84,11 @@ impl<'a> Scope<'a> {
     }
 
     /// Add (push) a new constant to the Scope.
+    ///
+    /// Constants are immutable and cannot be assigned to.  Their values never change.
+    /// Constants propagation is a technique used to optimize an AST.
+    /// However, in order to be used for optimization, constants must be in one of the recognized types:
+    /// `INT` (default to `i64`, `i32` if `only_i32`), `f64`, `String`, `char` and `bool`.
     pub fn push_constant<K: Into<Cow<'a, str>>, T: Any>(&mut self, name: K, value: T) {
         let value = value.into_dynamic();