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[alecthomas]

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[ThomasWidmann]

Hi, I am Thomas.

Have recently seen your parser implemented with go. Actually I have to cope with ldap based search filters and found your parser interesting. I am going to use this parser to interpret search filters but I think I haven't fully got how to approach this.

LDAP Filter

An ldap filter may look like this but could also be more complex using & (and) and |( or)

(&(objectClass=user)(objectCategory=person)(mail=a.b@cde.fg))

Approach to Parse

I have created the struct below to parse the filter but I immediately recognized that this is not working because

1. @Ident regular expression does create multiple tokens of mail address
2. & is seen as invalid character

Struct

// Ldapfilters
type Ldapfilters struct {
	Filter []*Ldapfilter `@@*`
}

// Ldapfilter
type Ldapfilter struct {
	Filtertype string          `"(" @("&" | "|")`
	Properties []*LdapProperty `@@* ")"`
}

// LdapProperty
type LdapProperty struct {
	Key string `"(" @Ident "="`
	Val string `@Ident")"`
}

Using Custom Lexer Definition

I tried to use a custom lever but I am not able to set it up properly. I am getting a compile error if I am getting a compile error when I do call participle.Build() or participle.MustBuild() - lever is not accepted. I think it is a type mismatch.

// LdapProperty
type EmailProperty struct {
	Key string `"(" @Ident "="`
	Val string `@MyVal")"`
}

func TestEmailToken(t *testing.T) {

	basicLexer, err := stateful.NewSimple([]stateful.Rule{
		{"Comment", `(?i)rem[^\n]*`, nil},
		{"String", `"(\\"|[^"])*"`, nil},
		{"Number", `[-+]?(\d*\.)?\d+`, nil},
		{"Ident", `[a-zA-Z_.@]\w*`, nil},
		{"MyVal", `[a-zA-Z_][a-zA-Z0-9_.@]{0,}`, nil},
		{"Punct", `[-[!@#$%^&*()+_={}\|:;"'<,>.?/]|]`, nil},
		{"EOL", `[\n\r]+`, nil},
		{"whitespace", `[ \t]+`, nil},
	})
	p3 := "(mail=a.b@cde.fg)"
	parser, err := participle.Build(
		&EmailProperty{},
		participle.Lexer(basicLexer),
	)
	ep := &EmailProperty{}
	err = parser.ParseString(p3, ep)

Probably someone can enlighten me :)

[alecthomas]

You haven't said what the exact error/issue is?

[ThomasWidmann]

The problem was sitting in front of the computer. I lost track with trial and error at some point. I copied the Basic Lexer and simply adjusted the regular expression at the type "Ident" so that I can parse a mail address as a value. This works fine now. I think the parser is really good, what did you originally build it for?