Ben's code #1
Ben's code #1
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…al-lab # Please enter a commit message to explain why this merge is necessary, # especially if it merges an updated upstream into a topic branch. # # Lines starting with '#' will be ignored, and an empty message aborts # the commit.
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| // factors | ||
| lazy val fact: PackratParser[Expr] = | ||
| number | ||
| ( number | ||
| | "("~>expr<~")" ) |
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How does this go about actually parsing the parenthetical expression? Why can you exclude something like ^^ {case "("~e~")" ⇒ (e)}? Does your use of expr direct the parser back up to the expression parser when a parenthetical expression is detected?
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A couple of things:
factshould give back anExpr(as specified in its result type:PackratParser[Expr])- The
~>and<~combinators throw away their left and right arguments, respectively.
So, the second rule will parse a left-paren, then parse an Expr, then parse a right-paren. It'll result in whatever expr results in, so we don't need a separate action to store it.
But, if we wanted to represent the fact that this expression was parenthetical, then we would add to the intermediate representation a case class for parenthetical expressions; and we would add an action to this rule to create an instance of that case class.
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