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Commit740d389

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CFG: Del transformation: Improvement and description of steps
1 parent80a0ebd commit740d389

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+58
-22
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1 file changed

+58
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‎src/ContextFreeGrammar/ContextFreeGrammar.ts‎

Lines changed: 58 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -344,21 +344,32 @@ export class ContextFreeGrammar {
344344
}
345345

346346
publicdel():ContextFreeGrammar;
347-
publicdel(step:(cfg:ContextFreeGrammar)=>void):ContextFreeGrammar;
348-
publicdel(step?:(cfg:ContextFreeGrammar)=>void):ContextFreeGrammar{
349-
constproductions=newMap<string,Production>();
347+
publicdel(step:StepCallback<ContextFreeGrammar>):ContextFreeGrammar;
348+
publicdel(step?:StepCallback<ContextFreeGrammar>):ContextFreeGrammar{
349+
constproductions=newMap<string,Array<Array<Token>>>([...this.productions].map(([nt,p])=>[nt,p.map(s=>[...s])]));
350350

351351
constnullableNonTerminals=newSet<string>(this.nullableNonTerminals());
352352
constnullNonTerminals=newSet<string>(this.nullNonTerminals(nullableNonTerminals));
353353

354-
for(const[nt,p]of[...this.productions].sort(([a,_a],[b,_b])=>sortBySymbolButFirst(a,b,this.start))){
354+
for(const[nt,p]of[...productions].sort(([a,_a],[b,_b])=>sortBySymbolButFirst(a,b,this.start))){
355+
letchangeHappened=false;
356+
letchangeDescription:string=null;
355357
if(!nullNonTerminals.has(nt)){
356-
constproduction=newArray<ReadonlyArray<Token>>();
358+
constfactoredOut=newArray<string>();
359+
constremoved=newArray<string>();
360+
letremovedEmpty=false;
361+
letproduction=newArray<Array<Token>>();
357362
for(constsofp){
358363
constsequences=newArray<Array<Token>>(newArray<Token>());
359364
for(consttokenofs){
360-
if(token.kind===TokenKind.Empty||
361-
(token.kind===TokenKind.NonTerminal&&nullNonTerminals.has(token.identifier))){
365+
if(token.kind===TokenKind.Empty){
366+
removedEmpty=true;
367+
changeHappened=true;
368+
continue;
369+
}
370+
elseif(token.kind===TokenKind.NonTerminal&&nullNonTerminals.has(token.identifier)){
371+
removed.push(token.identifier);
372+
changeHappened=true;
362373
continue;
363374
}
364375
elseif(token.kind===TokenKind.NonTerminal&&nullableNonTerminals.has(token.identifier)){
@@ -367,6 +378,8 @@ export class ContextFreeGrammar {
367378
sequences.push([...sequences[i]]);
368379
sequences[i].push(token);
369380
}
381+
factoredOut.push(token.identifier);
382+
changeHappened=true;
370383
}
371384
else{
372385
for(constsequenceofsequences){
@@ -376,21 +389,44 @@ export class ContextFreeGrammar {
376389
}
377390
production.push(...sequences.filter(s=>s.length>0));
378391
}
379-
productions.set(nt,production);
380-
step?.(newContextFreeGrammar(
381-
newSet<string>([
382-
...productions.keys(),
383-
...[...productions.values()].flatMap(p=>
384-
p.flatMap(s=>
385-
s.filter(t=>t.kind===TokenKind.NonTerminal)
386-
.map(t=>t.identifier)
387-
)
388-
)
389-
]),
390-
this.terminals,
391-
productions,
392-
this.start,
393-
));
392+
production=production.filter(a=>a.length>0);
393+
if(production.length>0){
394+
productions.set(nt,production);
395+
if(changeHappened){
396+
constchanges=newArray<string>();
397+
if(removed.length>0){
398+
changes.push(`null producing non-terminal${removed.length>1 ?"s" :""}${descriptionNaturalList(removed)} were removed`);
399+
}
400+
if(factoredOut.length>0){
401+
changes.push(`nullable non-terminal${factoredOut.length>1 ?"s" :""}${descriptionNaturalList(factoredOut)} were factored out`);
402+
}
403+
if(removedEmpty){
404+
changes.push("empty string tokens were removed");
405+
}
406+
changeDescription=`From the production of${nt},${descriptionNaturalList(changes)}.`;
407+
}
408+
}
409+
else{
410+
productions.delete(nt);
411+
changeHappened=true;
412+
changeDescription=`The non-terminal${nt} only produced the empty string, and where thus removed.`;
413+
}
414+
}
415+
else{
416+
productions.delete(nt);
417+
changeHappened=true;
418+
changeDescription=`The non-terminal${nt} only produced the empty string, and where thus removed.`;
419+
}
420+
if(changeHappened){
421+
step?.(
422+
newContextFreeGrammar(
423+
productions.keys(),
424+
this.terminals,
425+
productions,
426+
this.start,
427+
),
428+
changeDescription
429+
);
394430
}
395431
}
396432

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