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diff --git a/sucl/spine.dcl b/sucl/spine.dcl new file mode 100644 index 0000000..2ebe3a6 --- /dev/null +++ b/sucl/spine.dcl @@ -0,0 +1,193 @@ +definition module spine + +from rule import Rgraph,Rule +from pfun import Pfun +from basic import Optional + +/* + +spine.lit - The extended functional strategy +============================================ + +Description +----------- + +This script implements the strategy answer, and a function to compute it +for a given graph in a rewrite system. + +The strategy answer is a spine -- in principle a colon of partial +matches from patterns of rewrite rules to the graph, with at the bottom +the insteresting part: a redex, an open node or something else. See the +definition of subspine for that. + +The strategy function attempts to find a redex to reduce the graph to +normal form instead of root normal form. This is done by applying a +root normal form strategy recursively in preorder over the graph (of +course ignoring cycles). The node at which the root normal form +strategy was applied is returned in the strategy answer, so laziness can +be preserved. + +------------------------------------------------------------ + +Interface +--------- + +Exported identifiers: + +> %export +> answer || Strategy answer type +> foldspine || Higher order general spine folding +> ifopen || Check for answer indicating Open +> printanswer || Make a human-readable representation of an answer +> printspine || Make a human-readable representation of a spine +> showanswer || Make a representation of an answer +> showspine || Make a representation of a spine +> showsubspine || Make a representation of a subspine +> spine || Colon of partial matches +> spinenodes || Determine nodes in a spine +> spinetip || Determine bottom of spine +> subspine || Bottom of spine + +> history || Symbolic reduction history type +> printhistory || Make a human-readable representation of a history +> showhistory || Make a representation of a history + +Required types: + + subspine - rule@rule.lit,rgraph@rule.lit,pfun@pfun.lit + +------------------------------------------------------------ + +Includes +-------- + +> %include "basic.lit" || optional +> %include "pfun.lit" || pfun +> %include "graph.lit" || graph +> %include "rule.lit" || rgraph rule + +------------------------------------------------------------ + +Implementation +-------------- + + +Answer describes the answer of a strategy. Absence of a spine implies +that the node was in root normal form. + +> answer * ** *** == optional (spine * ** ***) + +> showanswer showa showb showc = showoptional (showspine showa showb showc) +> printanswer printa printb printc = foldoptional ["Rnf"] (printspine printa printb printc) + +*/ + +:: Answer sym var pvar + :== Optional (Spine sym var pvar) + +/* + +Spine describes the spine returned by a strategy. It contains the node +at which the strategy was applied, and the result for that node. + +> spine * ** *** == (**,subspine * ** ***) + +> showspine showa showb showc = showpair showb (showsubspine showa showb showc) + +> printspine printa printb printc +> = foldspine pair cycle delta force missingcase open partial unsafe redex strict +> where pair node (line,lines) = (printb node++" => "++line):lines +> cycle = ("Cycle",[]) +> delta = ("Delta",[]) +> force lines = ("Force",lines) +> missingcase = ("MissingCase",[]) +> open rgraph = ("Open "++printrgraph printa printc rgraph,[]) +> partial rule matching lines = ("Partial <fn> "++printrule printa printc rule++' ':printpfun printc printb matching,lines) +> unsafe rgraph = ("Unsafe "++printrgraph printa printb rgraph,[]) +> redex rule matching = ("Redex <fn> "++printrule printa printc rule++' ':printpfun printc printb matching,[]) +> strict = ("Strict",[]) + +*/ + +:: Spine sym var pvar + :== (var,Subspine sym var pvar) + +/* + +Subspine describes what was the result of the strategy applied to a node +in a graph. + +> subspine * ** *** +> ::= Cycle | || The spine contains a cycle +> Delta | || An imported (delta) rule was found +> Force (spine * ** ***) | || Global strictness annotation forced evaluation of a subgraph +> MissingCase | || All alternatives failed for a function symbol +> Open (rgraph * ***) | || Need root normal form of open node for matching +> Partial (rule * ***) (pfun *** **) (spine * ** ***) | || A rule was strictly partially matched +> Unsafe (rgraph * **) | || Terminated due to immininent recursion +> Redex (rule * ***) (pfun *** **) | || Total match +> Strict || Need root normal form due to strictness + +> showsubspine showa showb showc +> = sh +> where sh Cycle = "Cycle" +> sh Delta = "Delta" +> sh (Force spine) = "(Force "++showspine showa showb showc spine++")" +> sh MissingCase = "MissingCase" +> sh (Open rgraph) = "(Open "++showrgraph showa showc rgraph++")" +> sh (Partial rule matching spine) = "(Partial "++showrule showa showc rule++' ':showpfun showc showb matching++' ':showspine showa showb showc spine++")" +> sh (Unsafe rgraph) = "(Unsafe "++showrgraph showa showb rgraph++")" +> sh (Redex rule matching) = "(Redex "++showrule showa showc rule++' ':showpfun showc showb matching++")" +> sh Strict = "Strict" + + printsubspine printa printb printc + = pr + where pr Cycle = "Cycle" + pr Delta = "Delta" + pr (Force spine) = "(Force "++printspine printa printb printc spine++")" + pr MissingCase = "MissingCase" + pr (Open rgraph) = "(Open "++printrgraph printa printc rgraph++")" + pr (Partial rule matching spine) = "(Partial "++printrule printa printc rule++' ':printpfun printc printb matching++' ':printspine printa printb printc spine++")" + pr (Unsafe rgraph) = "(Unsafe "++printrgraph printa printb rgraph++")" + pr (Redex rule matching) = "(Redex "++printrule printa printc rule++' ':printpfun printc printb matching++")" + pr Strict = "Strict" + +*/ + +:: Subspine sym var pvar + = Cycle // The spine contains a cycle + | Delta // An imported (delta) rule was found + | Force (Spine sym var pvar) // Global strictness annotation forced evaluation of a subgraph + | MissingCase // All alternatives failed for a function symbol + | Open (Rgraph sym pvar) // Need root normal form of open node for matching + | Partial (Rule sym pvar) (Pfun pvar var) (Spine sym var pvar) // A rule was strictly partially matched + | Unsafe (Rgraph sym var) // Terminated due to immininent recursion + | Redex (Rule sym pvar) (Pfun pvar var) // Total match + | Strict // Need root normal form due to strictness + +// Fold up a spine using a function for each constructor +foldspine + :: !(var .subresult -> .result) + .subresult + .subresult + (.result -> .subresult) + .subresult + ((Rgraph sym pvar) -> .subresult) + ((Rule sym pvar) (Pfun pvar var) .result -> .subresult) + ((Rgraph sym var) -> .subresult) + ((Rule sym pvar) (Pfun pvar var) -> .subresult) + .subresult + .(Spine sym var pvar) + -> .result + +// Get the tip of a spine, +// i.e. the last part when all Partial's and Force's are stripped. +spinetip :: !(Spine sym var pvar) -> Spine sym var pvar + +// Get the main nodes of a spine, +// i.e. where the spine constructors are applied +// (not the matched nodes of partial matchings) +spinenodes :: .(Spine sym var pvar) -> [var] + +// Make a decision (continuation based) on whether a spine ends in Open +ifopen :: result result !.(Answer sym var pvar) -> result |