Specify grammar syntax with a grammar

Author: willfaught

README.md

@@ -4,10 +4,15 @@ Package ebnf represents and parses a variant of [Extended Backus-Naur Form](http
 
 Grammars are written like so:
 
-	Expression = Term {("+" | "-") Term}.
-	Term = Factor {("*" | "/") Factor}.
-	Factor = Number | "(" Expression ")".
-	Number = Digit {Digit}.
-	Digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9".
+	Grammar = {Production}.
+	Production = Identifier "=" Expression ".".
+	Expression = Term {"|" Term}.
+	Term = Factor {Factor}.
+	Factor = Group | Identifier | Literal | Option | Repetition.
+	Group = "(" Expression ")".
+	Identifier = letter {letter}.
+	Literal = "\"" {character} "\"".
+	Option = "[" Expression "]".
+	Repetition = "{" Expression "}".
 
 They can be parsed by [Parse](https://pkg.go.dev/github.com/willfaught/ebnf#Parse) into a [Grammar](https://pkg.go.dev/github.com/willfaught/ebnf#Grammar). [Grammar.Validate](https://pkg.go.dev/github.com/willfaught/ebnf#Grammar.Validate) determines whether a grammar is valid. [Grammar.First](https://pkg.go.dev/github.com/willfaught/ebnf#Grammar.First) and [Grammar.Follow](https://pkg.go.dev/github.com/willfaught/ebnf#Grammar.Follow) compute the first and follow sets for nonterminal identifiers. [Grammar.LL1](https://pkg.go.dev/github.com/willfaught/ebnf#Grammar.LL1) determines whether a valid grammar can be parsed by an LL(1) parser.

ebnf.go

@@ -7,11 +7,16 @@
 //
 // Grammars are written like so:
 //
-//	Expression = Term {("+" | "-") Term}.
-//	Term = Factor {("*" | "/") Factor}.
-//	Factor = Number | "(" Expression ")".
-//	Number = Digit {Digit}.
-//	Digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9".
+//	Grammar = {Production}.
+//	Production = Identifier "=" Expression ".".
+//	Expression = Term {"|" Term}.
+//	Term = Factor {Factor}.
+//	Factor = Group | Identifier | Literal | Option | Repetition.
+//	Group = "(" Expression ")".
+//	Identifier = letter {letter}.
+//	Literal = "\"" {character} "\"".
+//	Option = "[" Expression "]".
+//	Repetition = "{" Expression "}".
 //
 // They can be parsed by [Parse] into a [Grammar].
 // [Grammar.Validate] determines whether a grammar is valid.

ebnf_test.go

@@ -245,6 +245,17 @@ TA = F TB.
 TB = "*" F TB | "".
 F = id | "(" EA ")".`
 
+const wsn = `Grammar = {Production}.
+Production = Identifier "=" Expression ".".
+Expression = Term {"|" Term}.
+Term = Factor {Factor}.
+Factor = Group | Identifier | Literal | Option | Repetition.
+Group = "(" Expression ")".
+Identifier = letter {letter}.
+Literal = "\"" {character} "\"".
+Option = "[" Expression "]".
+Repetition = "{" Expression "}".`
+
 func TestParseValid(t *testing.T) {
 	t.Parallel()
 	for _, test := range []string{
@@ -293,6 +304,7 @@ func TestParseValidateValid(t *testing.T) {
 		arith,
 		modula2,
 		oberon2,
+		wsn,
 	} {
 		t.Log(test)
 		g, err := Parse(test)