func Identifier(l *lex.Lexer) lex.StateFn {
typ := ItemIdentifier
r, _ := utf8.DecodeRuneInString(l.Input[l.Start:])
if r == '!' {
l.Ignore()
typ = ItemBuiltin
}
for {
// should not appear in the first identifier of an expression of sub-expression (since it must be a function)
r = l.Next()
if r == ':' {
typ = ItemArgKey
l.Backup()
l.Emit(typ)
l.Next()
l.Ignore()
return InsideAction
}
if !IsValidIdentifierChar(r) {
l.Backup()
break
}
}
l.Emit(typ)
return InsideAction
}