diff options
author | Eduardo Julian | 2017-05-30 21:35:37 -0400 |
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committer | Eduardo Julian | 2017-05-30 21:35:37 -0400 |
commit | b73f1c909d19d5492d6d9a7dc707a3b817c73619 (patch) | |
tree | 369d957687852bb5ca0024e9175072f5c92bf6d1 /new-luxc/source/luxc/analyser/case/coverage.lux | |
parent | 56b0ca377a30e30bf832d6dfdb789676f67e7ade (diff) |
- Documented the analysis phase.
- Some refactoring.
- Removed singleton variants.
Diffstat (limited to 'new-luxc/source/luxc/analyser/case/coverage.lux')
-rw-r--r-- | new-luxc/source/luxc/analyser/case/coverage.lux | 287 |
1 files changed, 287 insertions, 0 deletions
diff --git a/new-luxc/source/luxc/analyser/case/coverage.lux b/new-luxc/source/luxc/analyser/case/coverage.lux new file mode 100644 index 000000000..754e555b2 --- /dev/null +++ b/new-luxc/source/luxc/analyser/case/coverage.lux @@ -0,0 +1,287 @@ +(;module: + lux + (lux (control monad + eq) + (data [bool "B/" Eq<Bool>] + [number] + ["R" result "R/" Monad<Result>] + (coll [list "L/" Fold<List>] + ["D" dict]))) + (luxc (lang ["la" analysis]))) + +## The coverage of a pattern-matching expression summarizes how well +## all the possible values of an input are being covered by the +## different patterns involved. +## Ideally, the pattern-matching has "total" coverage, which just +## means that every possible value can be matched by at least 1 +## pattern. +## Every other coverage is considered partial, and it would be valued +## as insuficient (since it could lead to runtime errors due to values +## not being handled by any pattern). +## The #Partial tag covers arbitrary partial coverages in a general +## way, while the other tags cover more specific cases for booleans +## and variants. +(type: #export #rec Coverage + #Partial + (#Bool Bool) + (#Variant Nat (D;Dict Nat Coverage)) + (#Seq Coverage Coverage) + (#Alt Coverage Coverage) + #Total) + +(def: #export (total? coverage) + (-> Coverage Bool) + (case coverage + (#Total _) + true + + _ + false)) + +(def: #export (determine pattern) + (-> la;Pattern Coverage) + (case pattern + ## Binding amounts to total coverage because any value can be + ## matched that way. + ## Unit [] amounts to total coverage because there is only one + ## possible value, so matching against it covers all cases. + (^or (#la;BindP _) (^ (#la;TupleP (list)))) + #Total + + (^ (#la;TupleP (list singleton))) + (determine singleton) + + ## Primitive patterns always have partial coverage because there + ## are too many possibilities as far as values go. + (^or (#la;NatP _) (#la;IntP _) (#la;DegP _) + (#la;RealP _) (#la;CharP _) (#la;TextP _)) + #Partial + + ## Bools are the exception, since there is only "true" and + ## "false", which means it is possible for boolean + ## pattern-matching to become total if complementary parts meet. + (#la;BoolP value) + (#Bool value) + + ## Tuple patterns can be total if there is totality for all of + ## their sub-patterns. + (#la;TupleP subs) + (loop [subs subs] + (case subs + #;Nil + #Total + + (#;Cons sub subs') + (let [post (recur subs')] + (if (total? post) + (determine sub) + (#Seq (determine sub) + post))))) + + ## Variant patterns can be shown to be total if all the possible + ## cases are handled totally. + (#la;VariantP tag-id num-tags sub) + (#Variant num-tags + (|> (D;new number;Hash<Nat>) + (D;put tag-id (determine sub)))))) + +(def: (xor left right) + (-> Bool Bool Bool) + (or (and left (not right)) + (and (not left) right))) + +## The coverage checker not only verifies that pattern-matching is +## total, but also that there are no redundant patterns. +## Redundant patterns will never be executed, since there will +## always be a pattern prior to them that would match the input. +## Because of that, the presence of redundant patterns is assumed to +## be a bug, likely due to programmer carelessness. +(def: redundant-pattern + (R;Result Coverage) + (R;fail "Redundant pattern.")) + +(def: (flatten-alt coverage) + (-> Coverage (List Coverage)) + (case coverage + (#Alt left right) + (list& left (flatten-alt right)) + + _ + (list coverage))) + +(struct: _ (Eq Coverage) + (def: (= reference sample) + (case [reference sample] + [#Total #Total] + true + + [(#Bool sideR) (#Bool sideS)] + (B/= sideR sideS) + + [(#Variant allR casesR) (#Variant allS casesS)] + (and (n.= allR allS) + (:: (D;Eq<Dict> =) = casesR casesS)) + + [(#Seq leftR rightR) (#Seq leftS rightS)] + (and (= leftR leftS) + (= rightR rightS)) + + [(#Alt _) (#Alt _)] + (let [flatR (flatten-alt reference) + flatS (flatten-alt sample)] + (and (n.= (list;size flatR) (list;size flatS)) + (list;every? (function [[coverageR coverageS]] + (= coverageR coverageS)) + (list;zip2 flatR flatS)))) + + _ + false))) + +(open Eq<Coverage> "C/") + +## After determining the coverage of each individual pattern, it is +## necessary to merge them all to figure out if the entire +## pattern-matching expression is total and whether it contains +## redundant patterns. +(def: #export (merge addition so-far) + (-> Coverage Coverage (R;Result Coverage)) + (case [addition so-far] + ## The addition cannot possibly improve the coverage. + [_ #Total] + redundant-pattern + + ## The addition completes the coverage. + [#Total _] + (R/wrap #Total) + + [#Partial #Partial] + (R/wrap #Partial) + + ## 2 boolean coverages are total if they compliment one another. + (^multi [(#Bool sideA) (#Bool sideSF)] + (xor sideA sideSF)) + (R/wrap #Total) + + [(#Variant allA casesA) (#Variant allSF casesSF)] + (cond (not (n.= allSF allA)) + (R;fail "Variants do not match.") + + (:: (D;Eq<Dict> Eq<Coverage>) = casesSF casesA) + redundant-pattern + + ## else + (do R;Monad<Result> + [casesM (foldM @ + (function [[tagA coverageA] casesSF'] + (case (D;get tagA casesSF') + (#;Some coverageSF) + (do @ + [coverageM (merge coverageA coverageSF)] + (wrap (D;put tagA coverageM casesSF'))) + + #;None + (wrap (D;put tagA coverageA casesSF')))) + casesSF (D;entries casesA))] + (wrap (if (let [case-coverages (D;values casesM)] + (and (n.= allSF (list;size case-coverages)) + (list;every? total? case-coverages))) + #Total + (#Variant allSF casesM))))) + + [(#Seq leftA rightA) (#Seq leftSF rightSF)] + (case [(C/= leftSF leftA) (C/= rightSF rightA)] + ## There is nothing the addition adds to the coverage. + [true true] + redundant-pattern + + ## The 2 sequences cannot possibly be merged. + [false false] + (R/wrap (#Alt so-far addition)) + + ## Same prefix + [true false] + (do R;Monad<Result> + [rightM (merge rightA rightSF)] + (if (total? rightM) + ## If all that follows is total, then it can be safely dropped + ## (since only the "left" part would influence whether the + ## merged coverage is total or not). + (wrap leftSF) + (wrap (#Seq leftSF rightM)))) + + ## Same suffix + [false true] + (do R;Monad<Result> + [leftM (merge leftA leftSF)] + (wrap (#Seq leftM rightA)))) + + ## The left part will always match, so the addition is redundant. + (^multi [(#Seq left right) single] + (C/= left single)) + redundant-pattern + + ## The right part is not necessary, since it can always match the left. + (^multi [single (#Seq left right)] + (C/= left single)) + (R/wrap single) + + ## When merging a new coverage against one based on Alt, it may be + ## that one of the many coverages in the Alt is complementary to + ## the new one, so effort must be made to fuse carefully, to match + ## the right coverages together. + ## If one of the Alt sub-coverages matches the new one, the cycle + ## must be repeated, in case the resulting coverage can now match + ## other ones in the original Alt. + ## This process must be repeated until no further productive + ## merges can be done. + [_ (#Alt leftS rightS)] + (do R;Monad<Result> + [#let [fuse-once (: (-> Coverage (List Coverage) + (R;Result [(Maybe Coverage) + (List Coverage)])) + (function [coverage possibilities] + (loop [alts possibilities] + (case alts + #;Nil + (wrap [#;None (list coverage)]) + + (#;Cons alt alts') + (case (merge coverage alt) + (#R;Success altM) + (case altM + (#Alt _) + (do @ + [[success alts+] (recur alts')] + (wrap [success (#;Cons alt alts+)])) + + _ + (wrap [(#;Some altM) alts'])) + + (#R;Error error) + (R;fail error)) + ))))] + [success possibilities] (fuse-once addition (flatten-alt so-far))] + (loop [success success + possibilities possibilities] + (case success + (#;Some coverage') + (do @ + [[success' possibilities'] (fuse-once coverage' possibilities)] + (recur success' possibilities')) + + #;None + (case (list;reverse possibilities) + #;Nil + (R;fail "{ This is not supposed to happen... }") + + (#;Cons last prevs) + (wrap (L/fold (function [left right] (#Alt left right)) + last + prevs)))))) + + _ + (if (C/= so-far addition) + ## The addition cannot possibly improve the coverage. + redundant-pattern + ## There are now 2 alternative paths. + (R/wrap (#Alt so-far addition))))) |