Add support for anonymous functions in Rust.

README.md

@@ -175,6 +175,10 @@ fn main() -> Result<(), EvalAltResult>
 }
 ```
 
+`EvalAltResult` is a Rust `enum` containing all errors encountered during the parsing or evaluation process.
+
+### Script evaluation
+
 The type parameter is used to specify the type of the return value, which _must_ match the actual type or an error is returned.
 Rhai is very strict here. There are two ways to specify the return type - _turbofish_ notation, or type inference.
 
@@ -192,6 +196,8 @@ Evaluate a script file directly:
 let result = engine.eval_file::<i64>("hello_world.rhai".into())?;       // 'eval_file' takes a 'PathBuf'
 ```
 
+### Compiling scripts (to AST)
+
 To repeatedly evaluate a script, _compile_ it first into an AST (abstract syntax tree) form:
 
 ```rust
@@ -211,6 +217,8 @@ Compiling a script file is also supported:
 let ast = engine.compile_file("hello_world.rhai".into())?;
 ```
 
+### Calling Rhai functions from Rust
+
 Rhai also allows working _backwards_ from the other direction - i.e. calling a Rhai-scripted function from Rust via `call_fn`.
 
 ```rust
@@ -251,6 +259,37 @@ let result: i64 = engine.call_fn(&mut scope, &ast, "hello", () )?
 //                                                          ^^ unit = tuple of zero
 ```
 
+### Creating Rust anonymous functions from Rhai script
+
+[`AnonymousFn`]: #creating-rust-anonymous-functions-from-rhai-script
+
+It is possible to further encapsulate a script in Rust such that it essentially becomes a normal Rust function.
+This is accomplished via the `AnonymousFn` trait which contains `create_from_script` (as well as its associate
+method `create_from_ast`):
+
+```rust
+use rhai::{Engine, AnonymousFn};                // use 'AnonymousFn' for 'create_from_script'
+
+let engine = Engine::new();                     // create a new 'Engine' just for this
+
+let script = "fn calc(x, y) { x + y.len() < 42 }";
+
+// AnonymousFn takes two type parameters:
+//   1) a tuple made up of the types of the script function's parameters
+//   2) the return type of the script function
+//
+// 'func' will have type Box<dyn Fn(i64, String) -> Result<bool, EvalAltResult>> and is callable!
+let func = AnonymousFn::<(i64, String), bool>::create_from_script(
+//                       ^^^^^^^^^^^^^ function parameter types in tuple
+
+                engine,                         // the 'Engine' is consumed into the closure
+                script,                         // the script, notice number of parameters must match
+                "calc"                          // the entry-point function name
+)?;
+
+func(123, "hello".to_string())? == false;       // call the anonymous function
+```
+
 Raw `Engine`
 ------------
 
@@ -448,8 +487,8 @@ To call these functions, they need to be registered with the [`Engine`].
 
 ```rust
 use rhai::{Engine, EvalAltResult};
-use rhai::RegisterFn;                           // use `RegisterFn` trait for `register_fn`
+use rhai::RegisterFn;                           // use 'RegisterFn' trait for 'register_fn'
-use rhai::{Any, Dynamic, RegisterDynamicFn};    // use `RegisterDynamicFn` trait for `register_dynamic_fn`
+use rhai::{Any, Dynamic, RegisterDynamicFn};    // use 'RegisterDynamicFn' trait for 'register_dynamic_fn'
 
 // Normal function
 fn add(x: i64, y: i64) -> i64 {
@@ -536,7 +575,7 @@ and the error text gets converted into `EvalAltResult::ErrorRuntime`.
 
 ```rust
 use rhai::{Engine, EvalAltResult, Position};
-use rhai::RegisterResultFn;                         // use `RegisterResultFn` trait for `register_result_fn`
+use rhai::RegisterResultFn;                         // use 'RegisterResultFn' trait for 'register_result_fn'
 
 // Function that may fail
 fn safe_divide(x: i64, y: i64) -> Result<i64, EvalAltResult> {

src/api.rs

@@ -1,9 +1,9 @@
 //! Module that defines the extern API of `Engine`.
 
 use crate::any::{Any, AnyExt, Dynamic};
-use crate::call::FuncArgs;
 use crate::engine::{make_getter, make_setter, Engine, FnAny, FnSpec};
 use crate::error::ParseError;
+use crate::fn_call::FuncArgs;
 use crate::fn_register::RegisterFn;
 use crate::parser::{lex, parse, parse_global_expr, Position, AST};
 use crate::result::EvalAltResult;

src/fn_anonymous.rs

@@ -0,0 +1,118 @@
+//! Module which defines the function registration mechanism.
+#![cfg(not(feature = "no_function"))]
+#![allow(non_snake_case)]
+
+use crate::any::Any;
+use crate::engine::Engine;
+use crate::error::ParseError;
+use crate::parser::AST;
+use crate::result::EvalAltResult;
+use crate::scope::Scope;
+
+/// A trait to create a Rust anonymous function from a script.
+pub trait AnonymousFn<ARGS, RET> {
+    type Output;
+
+    /// Create a Rust anonymous function from an `AST`.
+    /// The `Engine` and `AST` are consumed and basically embedded into the closure.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # fn main() -> Result<(), rhai::EvalAltResult> {
+    /// use rhai::{Engine, AnonymousFn};                // use 'AnonymousFn' for 'create_from_ast'
+    ///
+    /// let engine = Engine::new();                     // create a new 'Engine' just for this
+    ///
+    /// let ast = engine.compile("fn calc(x, y) { x + y.len() < 42 }")?;
+    ///
+    /// // AnonymousFn takes two type parameters:
+    /// //   1) a tuple made up of the types of the script function's parameters
+    /// //   2) the return type of the script function
+    /// //
+    /// // 'func' will have type Box<dyn Fn(i64, String) -> Result<bool, EvalAltResult>> and is callable!
+    /// let func = AnonymousFn::<(i64, String), bool>::create_from_ast(
+    /// //                       ^^^^^^^^^^^^^ function parameter types in tuple
+    ///
+    ///                 engine,                         // the 'Engine' is consumed into the closure
+    ///                 ast,                            // the 'AST'
+    ///                 "calc"                          // the entry-point function name
+    /// );
+    ///
+    /// func(123, "hello".to_string())? == false;       // call the anonymous function
+    /// # Ok(())
+    /// # }
+    fn create_from_ast(self, ast: AST, entry_point: &str) -> Self::Output;
+
+    /// Create a Rust anonymous function from a script.
+    /// The `Engine` is consumed and basically embedded into the closure.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # fn main() -> Result<(), rhai::EvalAltResult> {
+    /// use rhai::{Engine, AnonymousFn};                // use 'AnonymousFn' for 'create_from_script'
+    ///
+    /// let engine = Engine::new();                     // create a new 'Engine' just for this
+    ///
+    /// let script = "fn calc(x, y) { x + y.len() < 42 }";
+    ///
+    /// // AnonymousFn takes two type parameters:
+    /// //   1) a tuple made up of the types of the script function's parameters
+    /// //   2) the return type of the script function
+    /// //
+    /// // 'func' will have type Box<dyn Fn(i64, String) -> Result<bool, EvalAltResult>> and is callable!
+    /// let func = AnonymousFn::<(i64, String), bool>::create_from_script(
+    /// //                       ^^^^^^^^^^^^^ function parameter types in tuple
+    ///
+    ///                 engine,                         // the 'Engine' is consumed into the closure
+    ///                 script,                         // the script, notice number of parameters must match
+    ///                 "calc"                          // the entry-point function name
+    /// )?;
+    ///
+    /// func(123, "hello".to_string())? == false;       // call the anonymous function
+    /// # Ok(())
+    /// # }
+    /// ```
+    fn create_from_script(
+        self,
+        script: &str,
+        entry_point: &str,
+    ) -> Result<Self::Output, ParseError>;
+}
+
+macro_rules! def_anonymous_fn {
+    () => {
+        def_anonymous_fn!(imp);
+    };
+    (imp $($par:ident),*) => {
+        impl<'e, $($par: Any + Clone,)* RET: Any + Clone> AnonymousFn<($($par,)*), RET> for Engine<'e>
+        {
+            #[cfg(feature = "sync")]
+            type Output = Box<dyn Fn($($par),*) -> Result<RET, EvalAltResult> + Send + Sync + 'e>;
+
+            #[cfg(not(feature = "sync"))]
+            type Output = Box<dyn Fn($($par),*) -> Result<RET, EvalAltResult> + 'e>;
+
+            fn create_from_ast(self, ast: AST, entry_point: &str) -> Self::Output {
+                let name = entry_point.to_string();
+
+                Box::new(move |$($par: $par),*| {
+                    self.call_fn::<_, RET>(&mut Scope::new(), &ast, &name, ($($par,)*))
+                })
+            }
+
+            fn create_from_script(self, script: &str, entry_point: &str) -> Result<Self::Output, ParseError> {
+                let ast = self.compile(script)?;
+                Ok(AnonymousFn::<($($par,)*), RET>::create_from_ast(self, ast, entry_point))
+            }
+        }
+    };
+    ($p0:ident $(, $p:ident)*) => {
+        def_anonymous_fn!(imp $p0 $(, $p)*);
+        def_anonymous_fn!($($p),*);
+    };
+}
+
+#[rustfmt::skip]
+def_anonymous_fn!(A, B, C, D, E, F, G, H, J, K, L, M, N, P, Q, R, S, T, U, V);

src/fn_register.rs

@@ -262,10 +262,6 @@ macro_rules! def_register {
 
         def_register!($($p),*);
     };
-//    (imp_pop) => {};
-//    (imp_pop $head:ident => $head_mark:ty => $head_param:ty $(,$tail:ident => $tail_mark:ty => $tp:ty)*) => {
-//        def_register!(imp $($tail => $tail_mark => $tp),*);
-//    };
 }
 
 #[rustfmt::skip]

src/lib.rs

@@ -61,9 +61,10 @@ extern crate alloc;
 mod any;
 mod api;
 mod builtin;
-mod call;
 mod engine;
 mod error;
+mod fn_anonymous;
+mod fn_call;
 mod fn_register;
 mod optimize;
 mod parser;
@@ -72,14 +73,17 @@ mod scope;
 mod stdlib;
 
 pub use any::{Any, AnyExt, Dynamic, Variant};
-pub use call::FuncArgs;
 pub use engine::Engine;
 pub use error::{ParseError, ParseErrorType};
+pub use fn_call::FuncArgs;
 pub use fn_register::{RegisterDynamicFn, RegisterFn, RegisterResultFn};
 pub use parser::{Position, AST, INT};
 pub use result::EvalAltResult;
 pub use scope::Scope;
 
+#[cfg(not(feature = "no_function"))]
+pub use fn_anonymous::AnonymousFn;
+
 #[cfg(not(feature = "no_index"))]
 pub use engine::Array;
 

tests/call_fn.rs

@@ -1,5 +1,5 @@
 #![cfg(not(feature = "no_function"))]
-use rhai::{Engine, EvalAltResult, ParseErrorType, Scope, INT};
+use rhai::{AnonymousFn, Engine, EvalAltResult, ParseErrorType, Scope, INT};
 
 #[test]
 fn test_fn() -> Result<(), EvalAltResult> {
@@ -59,3 +59,16 @@ fn test_call_fn() -> Result<(), EvalAltResult> {
 
     Ok(())
 }
+
+#[test]
+fn test_anonymous_fn() -> Result<(), EvalAltResult> {
+    let calc_func = AnonymousFn::<(INT, INT, INT), INT>::create_from_script(
+        Engine::new(),
+        "fn calc(x, y, z) { (x + y) * z }",
+        "calc",
+    )?;
+
+    assert_eq!(calc_func(42, 123, 9)?, 1485);
+
+    Ok(())
+}