ebnf_test.go

package participle_test

import (
	"strings"
	"testing"

	require "github.com/alecthomas/assert/v2"
	"github.com/alecthomas/participle/v2"
)

func TestEBNF(t *testing.T) {
	parser := mustTestParser[EBNF](t)
	expected := `
EBNF = Production* .
Production = <ident> "=" Expression+ "." .
Expression = Sequence ("|" Sequence)* .
Sequence = Term+ .
Term = <ident> | Literal | Range | Group | LookaheadGroup | EBNFOption | Repetition | Negation .
Literal = <string> .
Range = <string> "…" <string> .
Group = "(" Expression ")" .
LookaheadGroup = "(" "?" ("=" | "!") Expression ")" .
EBNFOption = "[" Expression "]" .
Repetition = "{" Expression "}" .
Negation = "!" Expression .
`
	require.Equal(t, strings.TrimSpace(expected), parser.String())
}

func TestEBNF_Other(t *testing.T) {
	type Grammar struct {
		PositiveLookahead string `  (?= 'good') @Ident`
		NegativeLookahead string `| (?! 'bad' | "worse") @Ident`
		Negation          string `| !("anything" | 'but')`
	}

	parser := mustTestParser[Grammar](t)
	expected := `Grammar = ((?= "good") <ident>) | ((?! "bad" | "worse") <ident>) | ~("anything" | "but") .`
	require.Equal(t, expected, parser.String())
}

type (
	EBNFUnion interface{ ebnfUnion() }

	EBNFUnionA struct {
		A string `@Ident`
	}

	EBNFUnionB struct {
		B string `@String`
	}

	EBNFUnionC struct {
		C string `@Float`
	}
)

func (EBNFUnionA) ebnfUnion() {}
func (EBNFUnionB) ebnfUnion() {}
func (EBNFUnionC) ebnfUnion() {}

func TestEBNF_Union(t *testing.T) {
	type Grammar struct {
		TheUnion EBNFUnion `@@`
	}

	parser := mustTestParser[Grammar](t, participle.Union[EBNFUnion](EBNFUnionA{}, EBNFUnionB{}, EBNFUnionC{}))
	require.Equal(t,
		strings.TrimSpace(`
Grammar = EBNFUnion .
EBNFUnion = EBNFUnionA | EBNFUnionB | EBNFUnionC .
EBNFUnionA = <ident> .
EBNFUnionB = <string> .
EBNFUnionC = <float> .
`),
		parser.String())
}