inductive Lean.HeadIndex : Type

Datastructure for representing the "head symbol" of an expression. It is the key of KExprMap. Examples:

• The head of f a is .const f
• The head of let x := 1; f x is .const f
• The head of fun x => fun is .lam

HeadIndex is a very simple index, and is used in situations where we want to find definitionally equal terms, but we want to minimize the search by checking only pairs of terms that have the same HeadIndex.

• fvar (fvarId : FVarId) : HeadIndex
• mvar (mvarId : MVarId) : HeadIndex
• const (constName : Name) : HeadIndex
• proj (structName : Name) (idx : Nat) : HeadIndex
• lit (litVal : Literal) : HeadIndex
• sort : HeadIndex
• lam : HeadIndex
• forallE : HeadIndex

instance Lean.instInhabitedHeadIndex : Inhabited HeadIndex

instance Lean.instBEqHeadIndex : BEq HeadIndex

instance Lean.instReprHeadIndex : Repr HeadIndex

def Lean.HeadIndex.hash : HeadIndex → UInt64

Hash code for a HeadIndex value.

instance Lean.instHashableHeadIndex : Hashable HeadIndex

def Lean.Expr.headNumArgs (e : Expr) : Nat

Return the number of arguments in the given expression with respect to its HeadIndex

def Lean.Expr.headNumArgs.go : Expr → Nat → Nat

def Lean.Expr.toHeadIndex (e : Expr) : HeadIndex

Convert the given expression into a HeadIndex.