Agda.TypeChecking.Coverage.Match

Documentation

match :: [Clause] -> [Arg Pattern] -> Permutation -> Match Nat

Given

1. the function clauses cs 2. the patterns ps and permutation perm of a split clause

we want to compute a variable index of the split clause to split on next.

First, we find the set cs' of all the clauses that are instances (via substitutions rhos) of the split clause.

In these substitutions, we look for a column that has only constructor patterns. We try to split on this column first.

Match the given patterns against a list of clauses

data MPat

We use a special representation of the patterns we're trying to match against a clause. In particular we want to keep track of which variables are blocking a match.

Constructors

VarMP Nat

ConMP ConHead [Arg MPat]

LitMP Literal

WildMP

For dot patterns that cannot be turned into patterns.

ProjMP QName

Projection copattern.

buildMPatterns :: Permutation -> [Arg Pattern] -> [Arg MPat]

data Match a

If matching is inconclusive (Block) we want to know which variables are blocking the match.

Constructors

Yes a

Matches unconditionally.

No

Definitely does not match.

Block BlockingVars

Could match if non-empty list of blocking variables is instantiated properly.

BlockP

Could match if split on possible projections is performed.

Instances

Functor Match

Monoid a => Monoid (Match a)

Combine results of checking whether function clause patterns covers split clause patterns.

No is dominant: if one function clause pattern is disjoint to the corresponding split clause pattern, then the whole clauses are disjoint.

Yes is neutral: for a match, all patterns have to match.

Block accumulates variables of the split clause that have to be instantiated to make the split clause an instance of the function clause.

BlockP yields to Block, since blocking vars can also block the result type.

type BlockingVar = (Nat, Maybe [ConHead])

Nothing means there is an overlapping match for this variable. Just cons means that it is an non-overlapping match and cons are the encountered constructors.

type BlockingVars = [BlockingVar]

overlapping :: BlockingVars -> BlockingVars

zipBlockingVars :: BlockingVars -> BlockingVars -> BlockingVars

Left dominant merge of blocking vars.

choice :: Match a -> Match a -> Match a

choice m m' combines the match results m of a function clause with the (already combined) match results $m'$ of the later clauses. It is for skipping clauses that definitely do not match (No). It is left-strict, to be used with foldr. If one clause unconditionally matches (Yes) we do not look further.

type MatchLit = Literal -> MPat -> Match ()

noMatchLit :: MatchLit

yesMatchLit :: MatchLit

matchLits :: Clause -> [Arg Pattern] -> Permutation -> Bool

Check if a clause could match given generously chosen literals

matchClause :: MatchLit -> [Arg MPat] -> Nat -> Clause -> Match Nat

matchClause mlit qs i c checks whether clause c number i covers a split clause with patterns qs.

matchPats :: MatchLit -> [Arg Pattern] -> [Arg MPat] -> Match ()

matchPats mlit ps qs checks whether a function clause with patterns ps covers a split clause with patterns qs.

Issue 842: if in case of functions with varying arity, the split clause has proper patterns left, we refuse to match, because it would be troublesome to construct the split tree later. We would have to move bindings from the rhs to the lhs. For example, this is rejected: F : Bool -> Set1 F true = Set F = x -> Set

matchPat :: MatchLit -> Pattern -> MPat -> Match ()

matchPat mlit p q checks whether a function clause pattern p covers a split clause pattern q. There are three results: Yes () means it covers, because p is a variable pattern or q is a wildcard. No means it does not cover. Block [x] means p is a proper instance of q and could become a cover if q was split on variable x.