Struct arithmetic_eval::fns::Defer

pub struct Defer;

Allows to define a value recursively, by referencing a value being created.

It works like this:

• Provide a function as the only argument. The (only) argument of this function is the value being created.
• Do not use the uninitialized value synchronously; only use it in inner function definitions.
• Return the created value from a function.

Examples

let program = "
    recursive_fib = defer(|fib| {
        |n| if(n >= 0 && n <= 1, || n, || fib(n - 1) + fib(n - 2))()
    });
    recursive_fib(10)
";
let program = Untyped::<F32Grammar>::parse_statements(program)?;
let module = ExecutableModule::new("test_defer", &program)?;

let mut env = Environment::new();
env.extend(Comparisons::iter());
env.insert_native_fn("if", fns::If).insert_native_fn("defer", fns::Defer);
assert_eq!(module.with_env(&env)?.run()?, Value::Prim(55.0));

Trait Implementations

impl Clone for Defer

fn clone(&self) -> Defer

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Defer

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Defer

fn default() -> Defer

Returns the “default value” for a type.

impl<T: Clone + 'static> NativeFn<T> for Defer

fn evaluate( &self, args: Vec<SpannedValue<T>>, ctx: &mut CallContext<'_, T> ) -> EvalResult<T>

Executes the function on the specified arguments.

impl Copy for Defer