Pre and postconditions #
This module defines Assertion
and PostCond
, the types which constitute
the pre and postconditions of a Hoare triple in the program logic.
Predicate shapes #
Since WP
supports arbitrary monads, PostCond
must be general enough to
cope with state and exceptions.
For this reason, PostCond
is indexed by a PostShape
which is an abstraction
of the stack of effects supported by the monad, corresponding directly to
StateT
and ExceptT
layers in a transformer stack.
For every StateT σ
effect, we get one PostShape.arg σ
layer, whereas for every
ExceptT ε
effect, we get one PostShape.except ε
layer.
Currently, the only supported base layer is PostShape.pure
.
Pre and postconditions #
The type of preconditions Assertion ps
is distinct from the type of postconditions PostCond α ps
.
This is because postconditions not only specify what happens upon successful termination of the
program, but also need to specify a property that holds upon failure.
We get one "barrel" for the success case, plus one barrel per PostShape.except
layer.
It does not make much sense to talk about failure barrels in the context of preconditions.
Hence, Assertion ps
is defined such that all PostShape.except
layers are discarded from ps
,
via PostShape.args
.
Equations
- Std.Do.PostShape.pure.args = []
- (Std.Do.PostShape.arg σ s).args = σ :: s.args
- (Std.Do.PostShape.except ε s).args = s.args
Instances For
An assertion on the .arg
s in the given predicate shape.
example : Assertion (.arg ρ .pure) = (ρ → Prop) := rfl
example : Assertion (.except ε .pure) = Prop := rfl
example : Assertion (.arg σ (.except ε .pure)) = (σ → Prop) := rfl
example : Assertion (.except ε (.arg σ .pure)) = (σ → Prop) := rfl
This is an abbreviation for SPred
under the hood, so all theorems about SPred
apply.
Equations
- Std.Do.Assertion ps = Std.Do.SPred ps.args
Instances For
Encodes one continuation barrel for each PostShape.except
in the given predicate shape.
example : FailConds (.pure) = Unit := rfl
example : FailConds (.except ε .pure) = ((ε → Prop) × Unit) := rfl
example : FailConds (.arg σ (.except ε .pure)) = ((ε → Prop) × Unit) := rfl
example : FailConds (.except ε (.arg σ .pure)) = ((ε → σ → Prop) × Unit) := rfl
Equations
Instances For
Equations
- Std.Do.FailConds.const p = ()
- Std.Do.FailConds.const p = Std.Do.FailConds.const p
- Std.Do.FailConds.const p = (fun (_ε : ε) => ⌜p⌝, Std.Do.FailConds.const p)
Instances For
Equations
Instances For
Instances For
Equations
- Std.Do.instInhabitedFailConds = { default := Std.Do.FailConds.true }
Equations
- Std.Do.«term_⊢ₑ_» = Lean.ParserDescr.trailingNode `Std.Do.«term_⊢ₑ_» 25 26 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol " ⊢ₑ ") (Lean.ParserDescr.cat `term 25))
Instances For
Equations
- Std.Do.«term_∧ₑ_» = Lean.ParserDescr.trailingNode `Std.Do.«term_∧ₑ_» 35 36 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol " ∧ₑ ") (Lean.ParserDescr.cat `term 35))
Instances For
A multi-barreled postcondition for the given predicate shape.
example : PostCond α (.arg ρ .pure) = ((α → ρ → Prop) × Unit) := rfl
example : PostCond α (.except ε .pure) = ((α → Prop) × (ε → Prop) × Unit) := rfl
example : PostCond α (.arg σ (.except ε .pure)) = ((α → σ → Prop) × (ε → Prop) × Unit) := rfl
example : PostCond α (.except ε (.arg σ .pure)) = ((α → σ → Prop) × (ε → σ → Prop) × Unit) := rfl
Equations
- Std.Do.PostCond α s = ((α → Std.Do.Assertion s) × Std.Do.FailConds s)
Instances For
Equations
- One or more equations did not get rendered due to their size.
Instances For
A postcondition expressing partial correctness.
Equations
Instances For
Equations
- Std.Do.«term_⊢ₚ_» = Lean.ParserDescr.trailingNode `Std.Do.«term_⊢ₚ_» 25 26 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol " ⊢ₚ ") (Lean.ParserDescr.cat `term 25))
Instances For
Equations
- Std.Do.«term_∧ₚ_» = Lean.ParserDescr.trailingNode `Std.Do.«term_∧ₚ_» 35 36 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol " ∧ₚ ") (Lean.ParserDescr.cat `term 35))