Struct BuiltinFn 

pub struct BuiltinFn {
    pub name: &'static str,
    /* private fields */
}

A native Rust function that can be called from Swan code.

Why a newtype instead of a bare Rc<dyn Fn>?

1. Debug: dyn Fn is not Debug; storing a name gives meaningful output in error messages and test output.
2. Metadata: the name can be used when building Undefined error values (“function math.sin called on a Bool”).
3. Ergonomics: BuiltinFn::new("name", |arg| ...) is self-documenting.

Argument convention

The function receives the evaluated right-hand side as a single Value. Multi-argument calls arrive as Value::Tuple. The function is responsible for destructuring the tuple when it expects more than one argument.

Return value

The function must never panic. Return a Value::Undefined (for example with Value::undef_unary) for any input that is invalid.

Examples

use swan_core::value::{BuiltinFn, Value};

let negate = BuiltinFn::new("negate", |arg| match arg {
    Value::Numb(n) => Value::Numb(-n),
    other => Value::undef_unary("negate", other, 0),
});
assert_eq!(negate.call(Value::Numb(2.0)), Value::Numb(-2.0));

Fields

name: &'static str

Human-readable name, used in Debug output and error messages.

Implementations

impl BuiltinFn

pub fn new(name: &'static str, f: impl Fn(Value) -> Value + 'static) -> Self

Create a new built-in function from any Fn(Value) -> Value.

Both plain function pointers (fn(Value) -> Value) and closures are accepted because both coerce to dyn Fn(Value) -> Value.

pub fn call(&self, arg: Value) -> Value

Invoke the built-in with the given argument.

Trait Implementations

impl Clone for BuiltinFn

fn clone(&self) -> BuiltinFn

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for BuiltinFn

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

Formats the value using the given formatter.