Enum lambda_calculus::reduction::Order

pub enum Order {
    NOR,
    CBN,
    HSP,
    HNO,
    APP,
    CBV,
    HAP,
}

The evaluation order of β-reductions. The default is NOR (normal order).

They don't always yield the same result:

• The NOR, HNO, APP and HAP orders reduce expressions to their normal forms
• The APP order will fail to fully reduce expressions containing functions without a normal form, e.g. the Y combinator (they will expand forever)
• The CBN order reduces to weak head normal form
• The CBV order reduces to weak normal form
• The HSP order reduces to head normal form

Variants

NOR

Normal - leftmost outermost; the most popular lambda calculus reduction strategy

CBN

Call-by-name - leftmost outermost, but no reductions inside abstractions

HSP

Head spine - leftmost outermost, but abstractions reduced only in head position

HNO

Hybrid normal - a hybrid between HSP (head spine) and NOR (normal) strategies

APP

Applicative - leftmost innermost; the most eager strategy; unfit for recursion combinators

CBV

Call-by-value - leftmost innermost, but no reductions inside abstractions

HAP

Hybrid applicative - a hybrid between CBV (call-by-value) and APP (applicative) strategies; usually the fastest-reducing normalizing strategy

Trait Implementations

impl Debug for Order

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl PartialEq for Order

fn eq(&self, __arg_0: &Order) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl Display for Order

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

Formats the value using the given formatter.