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演算順序付きの難しい表現のパーサーを作りたいです。いくつかの例がありますが、動作が非常に遅く、例外 OutOfMemoryError がスローされます。どうすれば改善できますか？

def expr: Parser[Expression] = term5
def term5: Parser[Expression] =
    (term4 ~ "OR" ~ term4) ^^ { case lhs~o~rhs => BinaryOp("OR", lhs, rhs) } |
    term4
def term4: Parser[Expression] =
    (term3 ~ "AND" ~ term3) ^^ { case lhs~a~rhs => BinaryOp("AND", lhs, rhs) } |
    term3
def term3: Parser[Expression] =
    (term2 ~ "<>" ~ term2) ^^ { case lhs~ne~rhs => BinaryOp("NE", lhs, rhs) } |
    (term2 ~ "=" ~ term2) ^^ { case lhs~eq~rhs => BinaryOp("EQ", lhs, rhs) } |
    (term2 ~ "NE" ~ term2) ^^ { case lhs~ne~rhs => BinaryOp("NE", lhs, rhs) } |
    (term2 ~ "EQ" ~ term2) ^^ { case lhs~eq~rhs => BinaryOp("EQ", lhs, rhs) } |
    term2
def term2: Parser[Expression] =
    (term1 ~ "<" ~ term1) ^^ { case lhs~lt~rhs => BinaryOp("LT", lhs, rhs) } |
    (term1 ~ ">" ~ term1) ^^ { case lhs~gt~rhs => BinaryOp("GT", lhs, rhs) } |
    (term1 ~ "<=" ~ term1) ^^ { case lhs~le~rhs => BinaryOp("LE", lhs, rhs) } |
    (term1 ~ ">=" ~ term1) ^^ { case lhs~ge~rhs => BinaryOp("GE", lhs, rhs) } |
    (term1 ~ "LT" ~ term1) ^^ { case lhs~lt~rhs => BinaryOp("LT", lhs, rhs) } |
    (term1 ~ "GT" ~ term1) ^^ { case lhs~gt~rhs => BinaryOp("GT", lhs, rhs) } |
    (term1 ~ "LE" ~ term1) ^^ { case lhs~le~rhs => BinaryOp("LE", lhs, rhs) } |
    (term1 ~ "GE" ~ term1) ^^ { case lhs~ge~rhs => BinaryOp("GE", lhs, rhs) } |
    term1
def term1: Parser[Expression] =
    (term ~ "+" ~ term) ^^ { case lhs~plus~rhs => BinaryOp("+", lhs, rhs) } |
    (term ~ "-" ~ term) ^^ { case lhs~minus~rhs => BinaryOp("-", lhs, rhs) } |
    (term ~ ":" ~ term) ^^ { case lhs~concat~rhs => BinaryOp(":", lhs, rhs) } |
    term 
def term: Parser[Expression] =
    (factor ~ "*" ~ factor) ^^ { case lhs~times~rhs => BinaryOp("*", lhs, rhs) } |
    (factor ~ "/" ~ factor) ^^ { case lhs~div~rhs => BinaryOp("/", lhs, rhs) } |
    (factor ~ "MOD" ~ factor) ^^ { case lhs~div~rhs => BinaryOp("MOD", lhs, rhs) } |
    factor
def factor: Parser[Expression] =
    "(" ~> expr <~ ")" |
    ("+" | "-") ~ factor ^^ { case op~rhs => UnaryOp(op, rhs) } |
    function |
    numericLit ^^ { case x => Number(x/*.toFloat*/) } |
    stringLit ^^ { case s => Literal(s) } |
    ident ^^ { case id => Variable(id) }
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2 に答える 2

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私の最初の改善は次のようなものでした：

def term3: Parser[Expression] =
log((term2 ~ ("<>" | "=" | "NE" | "EQ") ~ term2) ^^ { case lhs~op~rhs => BinaryOp(op, lhs, rhs) })("term3 <>,=,NE,EQ") |
log(term2)("term3 term2")

OutOfMemoryError なしで動作しますが、遅くなります。doc/scala-devel-docs/examples/parsing/lambda/TestParser.scala を表示した後、次のソースを入手しました。

def expr: Parser[Expression] = term5
def term5: Parser[Expression] =
    log(chainl1(term4, term5, "OR" ^^ {o => (a: Expression, b: Expression) => BinaryOp(o, a, b)}))("term5 OR")
def term4: Parser[Expression] =
    log(chainl1(term3, term4, "AND" ^^ {o => (a: Expression, b: Expression) => BinaryOp(o, a, b)}))("term4 AND")
def term3: Parser[Expression] =
    log(chainl1(term2, term3, ("<>" | "=" | "NE" | "EQ") ^^ {o => (a: Expression, b: Expression) => BinaryOp(o, a, b)}))("term3 <>,=,NE,EQ")
def term2: Parser[Expression] =
    log(chainl1(term1, term2, ("<" | ">" | "<=" | ">=" | "LT" | "GT" | "LE" | "GE") ^^ {o => (a: Expression, b: Expression) => BinaryOp(o, a, b)}))("term2 <,>,...")
def term1: Parser[Expression] =
    log(chainl1(term, term1, ("+" | "-" | ":") ^^ {o => (a: Expression, b: Expression) => BinaryOp(o, a, b)}))("term1 +,-,:")
def term: Parser[Expression] =
    log(chainl1(factor, term, ("*" | "/" | "MOD") ^^ {o => (a: Expression, b: Expression) => BinaryOp(o, a, b)}))("term *,/,MOD")
def factor: Parser[Expression] =
    log("(" ~> expr <~ ")")("factor ()") |
    log(("+" | "-") ~ factor ^^ { case op~rhs => UnaryOp(op, rhs) })("factor unary") |
    log(function)("factor function") |
    log(numericLit ^^ { case x => Number(x/*.toFloat*/) })("factor numLit") |
    log(stringLit ^^ { case s => Literal(s) })("factor strLit") |
    log(ident ^^ { case id => Variable(id) })("factor ident")

それは速く働きます。申し訳ありませんが、chainl1 関数がソースを改善する方法を理解できません。仕組みがわかりません。

于 2011-12-21T10:27:15.240 に答える