Agda-2.6.4.1: A dependently typed functional programming language and proof assistant
Safe HaskellSafe-Inferred
LanguageHaskell2010

Agda.Termination.Order

Description

An Abstract domain of relative sizes, i.e., differences between size of formal function parameter and function argument in recursive call; used in the termination checker.

Synopsis

Structural orderings

data Order Source #

In the paper referred to above, there is an order R with Unknown <= Le <= Lt.

This is generalized to Unknown <= 'Decr k' where Decr 1 replaces Lt and Decr 0 replaces Le. A negative decrease means an increase. The generalization allows the termination checker to record an increase by 1 which can be compensated by a following decrease by 2 which results in an overall decrease.

However, the termination checker of the paper itself terminates because there are only finitely many different call-matrices. To maintain termination of the terminator we set a cutoff point which determines how high the termination checker can count. This value should be set by a global or file-wise option.

See Call for more information.

TODO: document orders which are call-matrices themselves.

Constructors

Decr !Bool !Int

Decrease of callee argument wrt. caller parameter.

The Bool indicates whether the decrease (if any) is usable. In any chain, there needs to be one usable decrease. Unusable decreases come from SIZELT constraints which are not in inductive pattern match or a coinductive copattern match. See issue #2331.

UPDATE: Andreas, 2017-07-26: Feature #2331 is unsound due to size quantification in terms. While the infrastructure for usable/unusable decrease remains in place, no unusable decreases are generated by TermCheck.

Unknown

No relation, infinite increase, or increase beyond termination depth.

Mat !(Matrix Int Order)

Matrix-shaped order, currently UNUSED.

Instances

Instances details
Pretty CallMatrix Source # 
Instance details

Defined in Agda.Termination.CallMatrix

Pretty Order Source # 
Instance details

Defined in Agda.Termination.Order

CallComb CallMatrix Source #

Call matrix multiplication.

f --(m1)--> g --(m2)--> h is combined to f --(m2 mul m1)--> h

Note the reversed order of multiplication: The matrix c1 of the second call g-->h in the sequence f-->g-->h is multiplied with the matrix c2 of the first call.

Preconditions: m1 has dimensions ar(g) × ar(f). m2 has dimensions ar(h) × ar(g).

Postcondition: m1 >*< m2 has dimensions ar(h) × ar(f).

Instance details

Defined in Agda.Termination.CallMatrix

NotWorse CallMatrix Source # 
Instance details

Defined in Agda.Termination.CallMatrix

NotWorse Order Source #

It does not get worse then `increase'. If we are still decreasing, it can get worse: less decreasing.

Instance details

Defined in Agda.Termination.Order

Methods

notWorse :: Order -> Order -> Bool Source #

HasZero Order Source # 
Instance details

Defined in Agda.Termination.Order

PartialOrd Order Source #

Information order: Unknown is least information. The more we decrease, the more information we have.

When having comparable call-matrices, we keep the lesser one. Call graph completion works toward losing the good calls, tending towards Unknown (the least information).

Instance details

Defined in Agda.Termination.Order

Show Order Source # 
Instance details

Defined in Agda.Termination.Order

Eq Order Source # 
Instance details

Defined in Agda.Termination.Order

Methods

(==) :: Order -> Order -> Bool Source #

(/=) :: Order -> Order -> Bool Source #

Ord Order Source # 
Instance details

Defined in Agda.Termination.Order

Diagonal (CallMatrixAug cinfo) Order Source # 
Instance details

Defined in Agda.Termination.CallMatrix

Methods

diagonal :: CallMatrixAug cinfo -> [Order] Source #

decr :: (?cutoff :: CutOff) => Bool -> Int -> Order Source #

Smart constructor for Decr k :: Order which cuts off too big values.

Possible values for k: - ?cutoff <= k <= ?cutoff + 1.

increase :: Int -> Order -> Order Source #

Raw increase which does not cut off.

decrease :: Int -> Order -> Order Source #

Raw decrease which does not cut off.

(.*.) :: (?cutoff :: CutOff) => Order -> Order -> Order Source #

Multiplication of Orders. (Corresponds to sequential composition.)

supremum :: (?cutoff :: CutOff) => [Order] -> Order Source #

The supremum of a (possibly empty) list of Orders. More information (i.e., more decrease) is bigger. Unknown is no information, thus, smallest.

infimum :: (?cutoff :: CutOff) => [Order] -> Order Source #

The infimum of a (non empty) list of Orders. Gets the worst information. Unknown is the least element, thus, dominant.

orderSemiring :: (?cutoff :: CutOff) => Semiring Order Source #

We use a record for semiring instead of a type class since implicit arguments cannot occur in instance constraints, like instance (?cutoff :: Int) => SemiRing Order.

le :: Order Source #

le, lt, decreasing, unknown: for backwards compatibility, and for external use.

lt :: Order Source #

Usable decrease.

orderMat :: Matrix Int Order -> Order Source #

Smart constructor for matrix shaped orders, avoiding empty and singleton matrices.

collapseO :: (?cutoff :: CutOff) => Order -> Order Source #

decreasing :: Order -> Bool Source #

Decreasing and usable?

isDecr :: Order -> Bool Source #

Matrix-shaped order is decreasing if any diagonal element is decreasing.

class NotWorse a where Source #

A partial order, aimed at deciding whether a call graph gets worse during the completion.

Methods

notWorse :: a -> a -> Bool Source #

Instances

Instances details
NotWorse CallMatrix Source # 
Instance details

Defined in Agda.Termination.CallMatrix

NotWorse Order Source #

It does not get worse then `increase'. If we are still decreasing, it can get worse: less decreasing.

Instance details

Defined in Agda.Termination.Order

Methods

notWorse :: Order -> Order -> Bool Source #

NotWorse (CallMatrixAug cinfo) Source # 
Instance details

Defined in Agda.Termination.CallMatrix

Methods

notWorse :: CallMatrixAug cinfo -> CallMatrixAug cinfo -> Bool Source #

(Ord i, HasZero o, NotWorse o) => NotWorse (Matrix i o) Source #

We assume the matrices have the same dimension.

Instance details

Defined in Agda.Termination.Order

Methods

notWorse :: Matrix i o -> Matrix i o -> Bool Source #

isOrder :: (?cutoff :: CutOff) => Order -> Bool Source #