Documentation

Init.Data.Ord

Swaps less and greater ordering results

@[macro_inline]

If o₁ and o₂ are Ordering, then o₁.then o₂ returns o₁ unless it is .eq, in which case it returns o₂. Additionally, it has "short-circuiting" semantics similar to boolean x && y: if o₁ is not .eq then the expression for o₂ is not evaluated. This is a useful primitive for constructing lexicographic comparator functions:

structure Person where
  name : String
  age : Nat

instance : Ord Person where
  compare a b := (compare a.name b.name).then (compare b.age a.age)

This example will sort people first by name (in ascending order) and will sort people with the same name by age (in descending order). (If all fields are sorted ascending and in the same order as they are listed in the structure, you can also use deriving Ord on the structure definition for the same effect.)

Equations

Check whether the ordering is 'equal'.

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Check whether the ordering is 'not equal'.

Check whether the ordering is 'less than or equal to'.

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Check whether the ordering is 'less than'.

Check whether the ordering is 'greater than'.

Check whether the ordering is 'greater than or equal'.

@[inline]
def compareOfLessAndEq {α : Type u_1} (x y : α) [LT α] [Decidable (x < y)] [DecidableEq α] :

Yields an Ordering s.t. x < y corresponds to Ordering.lt / Ordering.gt and x = y corresponds to Ordering.eq.

Equations
@[inline]
def compareOfLessAndBEq {α : Type u_1} (x y : α) [LT α] [Decidable (x < y)] [BEq α] :

Yields an Ordering s.t. x < y corresponds to Ordering.lt / Ordering.gt and x == y corresponds to Ordering.eq.

Equations
@[inline]
def compareLex {α : Sort u_1} {β : Sort u_2} (cmp₁ cmp₂ : αβOrdering) (a : α) (b : β) :

Compare a and b lexicographically by cmp₁ and cmp₂. a and b are first compared by cmp₁. If this returns 'equal', a and b are compared by cmp₂ to break the tie.

Equations
  • compareLex cmp₁ cmp₂ a b = (cmp₁ a b).then (cmp₂ a b)
class Ord (α : Type u) :

Ord α provides a computable total order on α, in terms of the compare : α → α → Ordering function.

Typically instances will be transitive, reflexive, and antisymmetric, but this is not enforced by the typeclass.

There is a derive handler, so appending deriving Ord to an inductive type or structure will attempt to create an Ord instance.

  • compare : ααOrdering

    Compare two elements in α using the comparator contained in an [Ord α] instance.

Instances
@[inline]
def compareOn {β : Type u_1} {α : Sort u_2} [ord : Ord β] (f : αβ) (x y : α) :

Compare x and y by comparing f x and f y.

instance instOrdNat :
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instance instOrdInt :
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instance instOrdBool :
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instance instOrdFin (n : Nat) :
Ord (Fin n)
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instance instOrdChar :
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instance instOrdOption {α : Type u_1} [Ord α] :
Ord (Option α)
def lexOrd {α : Type u_1} {β : Type u_2} [Ord α] [Ord β] :
Ord (α × β)

The lexicographic order on pairs.

Equations
def ltOfOrd {α : Type u_1} [Ord α] :
LT α
instance instDecidableRelLt {α : Type u_1} [Ord α] :
def leOfOrd {α : Type u_1} [Ord α] :
LE α
Equations
instance instDecidableRelLe {α : Type u_1} [Ord α] :
Equations
def Ord.toBEq {α : Type u_1} (ord : Ord α) :
BEq α

Derive a BEq instance from an Ord instance.

def Ord.toLT {α : Type u_1} :
Ord αLT α

Derive an LT instance from an Ord instance.

Equations
  • x.toLT = ltOfOrd
def Ord.toLE {α : Type u_1} :
Ord αLE α

Derive an LE instance from an Ord instance.

def Ord.opposite {α : Type u_1} (ord : Ord α) :
Ord α

Invert the order of an Ord instance.

Equations
  • ord.opposite = { compare := fun (x y : α) => compare y x }
def Ord.on {β : Type u_1} {α : Type u_2} :
Ord β(f : αβ) → Ord α

ord.on f compares x and y by comparing f x and f y according to ord.

Equations
def Ord.lex {α : Type u_1} {β : Type u_2} :
Ord αOrd βOrd (α × β)

Derive the lexicographic order on products α × β from orders for α and β.

Equations
  • x✝.lex x = lexOrd
def Ord.lex' {α : Type u_1} (ord₁ ord₂ : Ord α) :
Ord α

Create an order which compares elements first by ord₁ and then, if this returns 'equal', by ord₂.

def Ord.arrayOrd {α : Type u_1} [a : Ord α] :
Ord (Array α)

Creates an order which compares elements of an Array in lexicographic order.