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  • package org
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  • package benknoble
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  • package ebnf

    Provides classes for dealing with context-free grammars in EBNF form.

    Provides classes for dealing with context-free grammars in EBNF form.

    Provides a org.benknoble.ebnf.Grammar model, complete with scala DSL for creating complex grammars in code, and an org.benknoble.ebnf.EbnfParser to generate Grammars from a String.

    Overview

    The main class is org.benknoble.ebnf.Grammar:

    scala> val grammar = Grammar(
     |   new Production(
     |     Nonterminal('A),
     |     Alternation(Nonterminal('A),
     |     Sequence(Repetition(Terminal("abc")), Option(Terminal("def"))))))
grammar: org.benknoble.ebnf.Grammar = Grammar(List(Production(Nonterminal('A), Alternation(Nonterminal('A),Sequence(Repetition(Terminal(abc)),Option(Terminal(def)))))))

scala> val s = grammar.format
s: String = <A> ::= <A>|{'abc'}['def'] ;

    If you include org.benknoble.ebnf.ExprImplicits and take advantage of org.benknoble.ebnf.Expr syntax, it looks a lot cleaner:

    scala> val grammar = Grammar('A ::= 'A || Terminal("abc").* ~ "def".?)
grammar: org.benknoble.ebnf.Grammar = Grammar(List(Production(Nonterminal('A), Alternation(Nonterminal('A),Sequence(Repetition(Terminal(abc)),Option(Terminal(def)))))))

scala> val s = grammar.format
s: String = <A> ::= <A>|{'abc'}['def'] ;

    Finally, you can take advantage of org.benknoble.ebnf.EbnfParser:

    scala> val grammar = EbnfParser("<A> ::= <A>|{'abc'}['def'] ;")
grammar: Either[String,org.benknoble.ebnf.Grammar] = Right(Grammar(List(Production(Nonterminal('A), Alternation(Nonterminal('A),Sequence(Repetition(Terminal(abc)),Option(Terminal(def))))))))

scala> val msg = grammar.fold(s => s, g => g.format)
msg: String = <A> ::= <A>|{'abc'}['def'] ;
    Definition Classes
    benknoble
  • Alternation
  • EbnfParser
  • Expr
  • ExprImplicits
  • Grammar
  • Main
  • Nonterminal
  • Option
  • Production
  • Repetition
  • Sequence
  • Terminal
  • Word
  • ε
o

org.benknoble.ebnf

ExprImplicits

object ExprImplicits

Implicit conversions for Expr

Creates a DSL-like system, with Strings automatically converted to org.benknoble.ebnf.Terminals and Symbols converted to org.benknoble.ebnf.Nonterminal:

scala> import org.benknoble.ebnf._
import org.benknoble.ebnf._

scala> import ExprImplicits._
import ExprImplicits._

scala> val p = 'A ::= ("abc" || 'B.?) ~ 'C.*
p: org.benknoble.ebnf.Production = Production(Nonterminal('A), Sequence(Alternation(Terminal(abc),Option(Nonterminal('B))),Repetition(Nonterminal('C))))

scala> val f = p.format
f: String = <A> ::= ('abc'|[<B>]){<C>}

Do note that val r: Expr = "abc".* will not work, due to ambiguity:

scala> val r: Expr = "abc".*
<console>:17: error: type mismatch;
 found   : String("abc")
 required: ?{def *: ?}
Note that implicit conversions are not applicable because they are ambiguous:
 both method augmentString in object Predef of type (x: String)scala.collection.immutable.StringOps
 and method charToTerminal in object ExprImplicits of type (s: String)org.benknoble.ebnf.Terminal
 are possible conversion functions from String("abc") to ?{def *: ?}
       val r: Expr = "abc".*
                     ^
<console>:17: error: value * is not a member of String
       val r: Expr = "abc".*
                           ^
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