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reduce/resuce precedence #51

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reduce/resuce precedence #51

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f66e283
reduce/reduce and shift/reduce precedence
mrgleba Mar 23, 2016
faf82e7
New arguments
mrgleba May 30, 2016
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11 changes: 9 additions & 2 deletions src/FsYacc/fsyacc.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,8 @@ let out = ref None
let tokenize = ref false
let compat = ref false
let log = ref false
let newprec = ref false
let norec = ref false
let light = ref None
let inputCodePage = ref None
let mutable lexlib = "Microsoft.FSharp.Text.Lexing"
Expand All @@ -62,7 +64,9 @@ let usage =
ArgInfo("--tokens", ArgType.Set tokenize, "Simply tokenize the specification file itself.");
ArgInfo("--lexlib", ArgType.String (fun s -> lexlib <- s), "Specify the namespace for the implementation of the lexer (default: Microsoft.FSharp.Text.Lexing)");
ArgInfo("--parslib", ArgType.String (fun s -> parslib <- s), "Specify the namespace for the implementation of the parser table interpreter (default: Microsoft.FSharp.Text.Parsing)");
ArgInfo("--codepage", ArgType.Int (fun i -> inputCodePage := Some i), "Assume input lexer specification file is encoded with the given codepage."); ]
ArgInfo("--codepage", ArgType.Int (fun i -> inputCodePage := Some i), "Assume input lexer specification file is encoded with the given codepage.");
ArgInfo("--newprec", ArgType.Unit (fun () -> newprec := true), "Use the new precedence resolving behaviour. See: https://github.com/fsprojects/FsLexYacc/pull/51");
ArgInfo("--no-recovery", ArgType.Unit (fun () -> norec := true), "Don't try recovering from invalid input") ]

let _ = ArgParser.Parse(usage,(fun x -> match !input with Some _ -> failwith "more than one input given" | None -> input := Some x),"fsyacc <filename>")

Expand All @@ -89,6 +93,9 @@ let actionCoding action =

let main() =
let filename = (match !input with Some x -> x | None -> failwith "no input given") in
if not <| !newprec then
printfn "FSYACC is running in a compatibility mode - consider adding then --newprec argument"

let spec =
let stream,reader,lexbuf = UnicodeFileAsLexbuf(filename, !inputCodePage)
use stream = stream
Expand Down Expand Up @@ -147,7 +154,7 @@ let main() =
printfn "building tables";
let spec1 = ProcessParserSpecAst spec
let (prods,states, startStates,actionTable,immediateActionTable,gotoTable,endOfInputTerminalIdx,errorTerminalIdx,nonTerminals) =
CompilerLalrParserSpec logf spec1
CompilerLalrParserSpec logf !newprec !norec spec1

let (code,pos) = spec.Header
printfn "%d states" states.Length;
Expand Down
65 changes: 39 additions & 26 deletions src/FsYacc/fsyaccast.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -347,7 +347,7 @@ type PropagateTable() =


/// Compile a pre-processed LALR parser spec to tables following the Dragon book algorithm
let CompilerLalrParserSpec logf (spec : ProcessedParserSpec) =
let CompilerLalrParserSpec logf (newprec:bool) (norec:bool) (spec : ProcessedParserSpec) =
let stopWatch = new System.Diagnostics.Stopwatch()
let reportTime() = printfn "time: %A" stopWatch.Elapsed; stopWatch.Reset(); stopWatch.Start()
stopWatch.Start()
Expand Down Expand Up @@ -768,26 +768,39 @@ let CompilerLalrParserSpec logf (spec : ProcessedParserSpec) =
| (((precReduce,Reduce prodIdx) as reduceItem),
((precShift,Shift sIdx) as shiftItem)) ->
match precReduce, precShift with
| (ExplicitPrec (_,p1), ExplicitPrec(assocNew,p2)) ->
| (ExplicitPrec (_,p1) as pp, ExplicitPrec(assocNew,p2)) ->
if p1 < p2 then shiftItem
elif p1 > p2 then reduceItem
else
match assocNew with
| LeftAssoc -> reduceItem
| RightAssoc -> shiftItem
| NonAssoc ->
reportConflict shiftItem reduceItem "we preffer shift on equal precedences"
incr shiftReduceConflicts;
shiftItem
| NonAssoc ->
if newprec then
pp, Error
else
reportConflict shiftItem reduceItem "we preffer shift on equal precedences"
incr shiftReduceConflicts;
shiftItem
| _ ->
reportConflict shiftItem reduceItem "we preffer shift when unable to compare precedences"
incr shiftReduceConflicts;
shiftItem
| ((_,Reduce prodIdx1),(_, Reduce prodIdx2)) ->
"we prefer the rule earlier in the file"
|> if prodIdx1 < prodIdx2 then reportConflict itemSoFar itemNew else reportConflict itemNew itemSoFar
incr reduceReduceConflicts;
if prodIdx1 < prodIdx2 then itemSoFar else itemNew
| ((prec1,Reduce prodIdx1),(prec2, Reduce prodIdx2)) ->
match prec1, prec2 with
| (ExplicitPrec (_,p1), ExplicitPrec(assocNew,p2)) when newprec ->
if p1 < p2 then itemNew
elif p1 > p2 then itemSoFar
else
"we prefer the rule earlier in the file on equal precedences"
|> if prodIdx1 < prodIdx2 then reportConflict itemSoFar itemNew else reportConflict itemNew itemSoFar
incr reduceReduceConflicts;
if prodIdx1 < prodIdx2 then itemSoFar else itemNew
| _ ->
"we prefer the rule earlier in the file when unable to compare precedences"
|> if prodIdx1 < prodIdx2 then reportConflict itemSoFar itemNew else reportConflict itemNew itemSoFar
incr reduceReduceConflicts;
if prodIdx1 < prodIdx2 then itemSoFar else itemNew
| _ -> itemNew
arr.[termIdx] <- winner

Expand Down Expand Up @@ -840,29 +853,29 @@ let CompilerLalrParserSpec logf (spec : ProcessedParserSpec) =
let immediateAction =
match Set.toList closure with
| [item0] ->
let pItem0 = prodIdx_of_item0 item0
match (rsym_of_item0 item0) with
| None when (let reduceOrErrorAction = function Error | Reduce _ -> true | Shift _ | Accept -> false
termTab.Indexes |> List.forall(fun terminalIdx -> reduceOrErrorAction (snd(arr.[terminalIdx]))))
-> Some (Reduce (prodIdx_of_item0 item0))
| None when (termTab.Indexes |> List.forall(fun terminalIdx -> arr.[terminalIdx] |> function (_, Reduce pItem0) -> true | (_, Error) when not <| norec -> true | _ -> false))
-> Some (Reduce pItem0)

| None when (let acceptOrErrorAction = function Error | Accept -> true | Shift _ | Reduce _ -> false
List.forall (fun terminalIdx -> acceptOrErrorAction (snd(arr.[terminalIdx]))) termTab.Indexes)
| None when (termTab.Indexes |> List.forall(fun terminalIdx -> arr.[terminalIdx] |> function (_, Accept) -> true | (_, Error) when not <| norec -> true | _ -> false))
-> Some Accept

| _ -> None
| _ -> None

// A -> B C . rules give rise to reductions in favour of errors
for item0 in ComputeClosure0 kernel do
let prec = prec_of_item0 item0
match rsym_of_item0 item0 with
| None ->
for terminalIdx in termTab.Indexes do
if snd(arr.[terminalIdx]) = Error then
let prodIdx = prodIdx_of_item0 item0
let action = (prec, (if IsStartItem(item0) then Accept else Reduce prodIdx))
addResolvingPrecedence arr kernelIdx terminalIdx action
| _ -> ()
if not <| norec then
for item0 in ComputeClosure0 kernel do
let prec = prec_of_item0 item0
match rsym_of_item0 item0 with
| None ->
for terminalIdx in termTab.Indexes do
if snd(arr.[terminalIdx]) = Error then
let prodIdx = prodIdx_of_item0 item0
let action = (prec, (if IsStartItem(item0) then Accept else Reduce prodIdx))
addResolvingPrecedence arr kernelIdx terminalIdx action
| _ -> ()

arr,immediateAction

Expand Down