ebnf范式_使用Scala基于词法单元的解析器定制EBNF范式文法解析
前言
近期在做Oracle遷移到Spark平臺(tái)的項(xiàng)目上遇到了一些平臺(tái)公式翻譯為SparkSQL(on Hive)的需求，而Spark采用親媽語(yǔ)言Scala進(jìn)行開發(fā)。下面是個(gè)意外，被論文查重了,移步至我的Leanote博客查看點(diǎn)我，先亂碼一段時(shí)間[分后，擬使中的EB式，進(jìn)行基于@#@#@法解析。
平臺(tái)公式及翻譯后的SparkSQL
平臺(tái)公式的樣子如下所示：
if (XX1_m001[D003]="邢おb7骯α?薇" || XX1_m001[H003]
這里面字段值"邢おb7骯α?薇"為這個(gè)的目的是為了測(cè)試各種字符集是否都能匹配滿足。
那么對(duì)應(yīng)的SparkSQL應(yīng)該是這個(gè)樣子的,由于是使用的Hive on Spark，因而長(zhǎng)得跟Oracle的SQL語(yǔ)句差不多：
SELECT COUNT(H022) FROM XX1_m001 WHERE (XX1_m001.D003='邢おb7骯α?薇' OR XX1_m001.H003
總體而言比較簡(jiǎn)單，因?yàn)槲抑皇窍朐谶@里做一個(gè)Demo。
平臺(tái)公式的EBNF范式及詞法解析設(shè)計(jì)
expr-condition ::= tableName "[" valueName "]" comparator Condition
expr-front ::= expr-condition (("&&"|"||")expr-front)*
expr-back ::= tableName "[" valueName "," operator "]"
expr ::= "if" expr-front "then" expr-back
其中詞法定義如下
operator => [SUM,COUNT]
tableName,valueName =>ident #ident為關(guān)鍵字
comparator => ["=",">=","<=",">","
Condition => stringLit #stringLit為字符串常量
使用Scala基于詞法單元的解析器解析上述EBNF文法
Scala基于詞法單元的解析器是需要繼承StandardTokenParsers這個(gè)類的，該類提供了很方便的解析函數(shù)，以及詞法集合。
我們可以通過(guò)使用lexical.delimiters列表來(lái)存放在文法翻譯器執(zhí)行過(guò)程中遇到的分隔符，使用lexical.reserved列表來(lái)存放執(zhí)行過(guò)程中的關(guān)鍵字。
比如，我們參照平臺(tái)公式，看到"=",">=","<=",">","=","<=",">","
表現(xiàn)在代碼中是醬紫的：
lexical.delimiters += ("=",">=","<=",">","
lexical.reserved += ("if","then","SUM","COUNT")
是不是so easy~。
我們?cè)賮?lái)看一下如何使用基于詞法單元的解析器解析前面我們?cè)O(shè)計(jì)的EBNF文法呢。我在這里先上代碼：
class ExprParsre extends StandardTokenParsers{
lexical.delimiters += ("=",">=","<=",">","
lexical.reserved += ("if","then","SUM","COUNT")
def expr: Parser[String] = "if" ~ expr_front ~ "then" ~ expr_back ^^{
case "if" ~ exp1 ~ "then" ~ exp2 => exp2 + " WHERE " +exp1
}
def expr_priority: Parser[String] = opt("(") ~ expr_condition ~ opt(")") ^^{
case Some("(") ~ conditions ~ Some(")") => "(" + conditions +")"
case Some("(") ~ conditions ~ None => "(" + conditions
case None ~ conditions ~ Some(")") => conditions +")"
case None ~ conditions ~ None => conditions
}
def expr_condition: Parser[String] = ident ~ "[" ~ ident ~ "]" ~ ("="|">="|"<="|">"|"
case ident1~"["~ident2~"]"~"="~stringList => ident1 + "." + ident2 +"='" + stringList +"'"
case ident1~"["~ident2~"]"~">="~stringList => ident1 + "." + ident2 +">='" + stringList +"'"
case ident1~"["~ident2~"]"~"<="~stringList => ident1 + "." + ident2 +"<='" + stringList +"'"
case ident1~"["~ident2~"]"~">"~stringList => ident1 + "." + ident2 +">'" + stringList +"'"
case ident1~"["~ident2~"]"~" ident1 + "." + ident2 +"
case ident1~"["~ident2~"]"~"!="~stringList => ident1 + "." + ident2 +"!='" + stringList +"'"
}
def comparator: Parser[String] = ("&&"|"||") ^^{
case "&&" => " AND "
case "||" => " OR "
}
def expr_front: Parser[String] = expr_priority ~ rep(comparator ~ expr_priority) ^^{
case exp1 ~ exp2 => exp1 + exp2.map(x =>{x._1 + " " + x._2}).mkString(" ")
}
def expr_back: Parser[String] = ident ~ "[" ~ ident ~ "," ~ ("SUM"|"COUNT") ~ "]" ^^ {
case ident1~"["~ident2~","~"COUNT"~"]" => "SELECT COUNT("+ ident2.toString() +") FROM " + ident1.toString()
case ident1~"["~ident2~","~"SUM"~"]" => "SELECT SUM("+ ident2.toString() +") FROM " + ident1.toString()
}
def parserAll[T]( p : Parser[T], input :String) = {
phrase(p)( new lexical.Scanner(input))
}
}
總結(jié)
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