go-ungrammar

Ungrammar implementation and API in Go. Blog post for background.

Ungrammar is a DSL for concrete syntax trees (CST). This implementation is based on the original ungrammar crate, also borrowing some test files from it.

Ungrammar syntax

The syntax of Ungrammar files is very simple:

//           -- comment
Name =       -- non-terminal definition
'ident'      -- token (terminal)
A B          -- sequence
A | B        -- alternation
A*           -- repetition (zero or more)
A?           -- optional (zero or one)
(A B)        -- grouping elements for precedence control
label:A      -- label hint for naming

For some concrete examples, look at files in the testdata directory.

Usage

Usage example:

go-ungrammar/example_test.go

Lines 13 to 31 in 229d0dd

	func ExampleParseAndExamine() {
	input := `
	Foo = Bar Baz
	Baz = ( Kay Jay )* | 'id'`
	// Create an Ungrammar parser and parse input.
	p := ungrammar.NewParser(input)
	ungram, err := p.ParseGrammar()
	if err != nil {
	panic(err)
	}
	// Display the string representation of the parsed ungrammar.
	fmt.Println(ungram.Rules["Foo"].String())
	fmt.Println(ungram.Rules["Baz"].String())
	// Output:
	// Seq(Bar, Baz)
	// Alt(Rep(Seq(Kay, Jay)), 'id')
	}

For somewhat more sophisticated usage, see the cmd/ungrammar2json command.