Struct NeedPolicy 

pub struct NeedPolicy;

A call-by-need policy: arguments are thunked and forced at most once.

Each argument becomes a memoizing ThunkObject whose value is computed on first force and cached for later uses.

Trait Implementations

impl EvalPolicy for NeedPolicy

fn name(&self) -> &'static str

A stable, human-readable name for this policy.

fn allow_macro_expansion(&self, phase: Phase) -> bool

Whether macro expansion is permitted in the given Phase.

fn prepare_call_args( &self, cx: &mut Cx, raw: RawArgs, _demands: &[Demand], ) -> Result<PreparedArgs>

Prepares raw call arguments into PreparedArgs per the demands.

fn force(&self, cx: &mut Cx, value: Value, demand: Demand) -> Result<Value>

Forces value far enough to satisfy demand.

fn eval_expr(&self, cx: &mut Cx, expr: Expr) -> Result<Value>

Evaluates a bare expression to a value under this policy.

fn resolve_unbound_symbol(&self, cx: &mut Cx, symbol: Symbol) -> Result<Value>

Resolve a symbol that bound to nothing in value position.

fn resolve_unbound_call( &self, cx: &mut Cx, operator: Symbol, args: Vec<Expr>, ) -> Result<Value>

Resolve a call whose operator bound to nothing.