这是一阶 ODE 系统的语法:
system ::= equation { equation }
equation ::= variable "=" (arithExpr | param) "\n"
variable ::= algebraicVar | stateVar
algrebraicVar ::= identifier
stateVar ::= algebraicVar'
arithExpr ::= term { "+" term | "-" term }
term ::= factor { "*" factor | "/" factor }
factor ::= algebraicVar
| powerExpr
| floatingPointNumber
| functionCall
| "(" arithExpr ")"
powerExpr ::= arithExpr {"^" arithExpr}
笔记:
- 标识符应该是有效的 Scala 标识符。
- stateVar 是一个 algebraicVar 后跟一个撇号(x' 表示 x 的一阶导数——关于时间——)
- 我没有为 a 编写任何代码,
functionCall
但我的意思是Cos[Omega]
这是我已经拥有的
package tests
import scala.util.parsing.combinator.lexical.StdLexical
import scala.util.parsing.combinator.syntactical.StandardTokenParsers
import scala.util.parsing.combinator._
import scala.util.parsing.combinator.JavaTokenParsers
import token._
object Parser1 extends StandardTokenParsers {
lexical.delimiters ++= List("(", ")", "=", "+", "-", "*", "/", "\n")
lexical.reserved ++= List(
"Log", "Ln", "Exp",
"Sin", "Cos", "Tan",
"Cot", "Sec", "Csc",
"Sqrt", "Param", "'")
def system: Parser[Any] = repsep(equation, "\n")
def equation: Parser[Any] = variable ~ "=" ~ ("Param" | arithExpr )
def variable: Parser[Any] = stateVar | algebraicVar
def algebraicVar: Parser[Any] = ident
def stateVar: Parser[Any] = algebraicVar ~ "\'"
def arithExpr: Parser[Any] = term ~ rep("+" ~ term | "-" ~ term)
def term: Parser[Any] = factor ~ rep("*" ~ factor | "/" ~ factor)
def factor: Parser[Any] = algebraicVar | floatingPointNumber | "(" ~ arithExpr ~ ")"
def powerExpr: Parser[Any] = arithExpr ~ rep("^" ~ arithExpr)
def main(args: Array[String]) {
val code = "x1 = 2.5 * x2"
equation(new lexical.Scanner(code)) match {
case Success(msg, _) => println(msg)
case Failure(msg, _) => println(msg)
case Error(msg, _) => println(msg)
}
}
}
但是这条线不起作用:
def factor: Parser[Any] = algebraicVar | floatingPointNumber | "(" ~ arithExpr ~ ")"
因为我还没有定义什么是floatingPointNumber
. 首先,我尝试混合使用 JavaTokenParsers,但随后我得到了相互冲突的定义。我尝试使用 StandardTokenParsers 而不是 JavaTokenParsers 的原因是能够使用一组预定义的关键字
lexical.reserved ++= List(
"Log", "Ln", "Exp",
"Sin", "Cos", "Tan",
"Cot", "Sec", "Csc",
"Sqrt", "Param", "'")
我在 Scala 用户邮件列表 ( https://groups.google.com/forum/?fromgroups#!topic/scala-user/KXlfGauGR9Q ) 上问过这个问题,但我没有收到足够的回复。非常感谢您的帮助。