1 Analyse lexicale (7 points)

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1 Université de Nice-Sophia Antipolis U.E. Analyses (semestre 6) Licence d'informatique - 3e année Épreuve de contrôle continu N 1 du vendredi 21 mars 2008 Durée : 2 heures Tous documents autorisés 1 Analyse lexicale (7 s) Le RFC résume la syntaxe des adresses électroniques. En voici des extraits. Contemporary addresses consist of a "local part" separated from a "domain part" (a fully-qualified domain name) by an at-sign ("@"). The syntax of the domain part corresponds to that in the previous section. The concerns identified in that section about filtering and lists of names apply to the domain names used in an context as well. The domain name can also be replaced by an IP address in square brackets, but that form is strongly discouraged except for testing and troubleshooting purposes. The local part may appear using the quoting conventions described below. The quoted forms are rarely used in practice, but are required for some legitimate purposes. Hence, they should not be rejected in filtering routines but, should instead be passed to the system for evaluation by the destination host. The exact rule is that any ASCII character, including control characters, may appear quoted, or in a quoted string. When quoting is needed, the backslash character is used to quote the following character. For example "Abc\@def"@example.com is a valid form of an address. Blank spaces may also appear, as in "Fred\ Bloggs"@example.com The backslash character may also be used to quote itself, e.g., "Joe.\\Blow"@example.com In addition to quoting using the backslash character, conventional double-quote characters may be used to surround strings. For example "Abc@def"@example.com "Fred Bloggs"@example.com are alternate forms of the first two examples above. These quoted 1 Request For Comments.

2 2 forms are rarely recommended, and are uncommon in practice, but, as discussed above, must be supported by applications that are processing addresses. In particular, the quoted forms often appear in the context of addresses associated with transitions from other systems and contexts; those transitional requirements do still arise and, since a system that accepts a user-provided address cannot "know" whether that address is associated with a legacy system, the address forms must be accepted and passed into the environment. Without quotes, local-parts may consist of any combination of alphabetic characters, digits, or any of the special characters! # $ % & ' * + - / =? ^ _ `. { ~ period (".") may also appear, but may not be used to start or end the local part, nor may two or more consecutive periods appear. Stated differently, any ASCII graphic (printing) character other than the at-sign ("@"), backslash, double quote, comma, or square brackets may appear without quoting. If any of that list of excluded characters are to appear, they must be quoted. Forms such as user+mailbox@example.com customer/department=shipping@example.com $A12345@example.com!def!xyz%abc@example.com _somename@example.com are valid and are seen fairly regularly, but any of the characters listed above are permitted. In the context of local parts, apostrophe ("'") and acute accent ("`") are ordinary characters, not quoting characters. Some of the characters listed above are used in conventions about routing or other types of special handling by some receiving hosts. But, since there is no way to know whether the remote host is using those conventions or just treating these characters as normal text, sending programs (and programs evaluating address validity) must simply accept the strings and pass them on. In addition to restrictions on syntax, there is a length limit on addresses. That limit is a maximum of 64 characters (octets) in the "local part" (before the "@") and a maximum of 255 characters (octets) in the domain part (after the "@") for a total length of 320 characters. However, there is a restriction in RFC 2821 on the length of an address in MAIL and RCPT commands of 256 characters. Since addresses that do not fit in those fields are not normally useful, the upper limit on address lengths should normally be considered to be 256. Questions : 1. Dessinez le diagramme d'états permettant de reconnaître une adresse électronique telle que décrite par la norme (on ne tient pas compte de la longueur limite). On se limitera pour le nom du domaine à la syntaxe suivante (nom étant une suite de caractères s minuscules)

3 3 nom 1 "."nom 2 "."..."."nom n Vous pouvez commencer par décrire la local-part sans guillemets, et ensuite agrandir votre diagramme. " ASCII \ car. permis \ 2. Quelle description doit-on donner à Flex pour que la fonction yylex produite renvoie 1 si le texte lu sur yyin est considéré comme une adresse électronique valide, 0 si ce n'est pas le cas. On tient compte cette fois des longueurs limites. localpart " \, ] + d o m a i n p a r t [ a za Z]+ ". " [ a za Z]+ %{ #i n c l u d e < s t d l i b. h> #i n c l u d e < s t r i n g s. h> i n t t e s t l g ( c h a r s ) { i n t l l p, l d p ; c h a r a t = s t r c h r ( s, '@ ' ) ; l l p = ( a t s ) / s i z e o f ( c h a r ) ; l d p = s t r l e n ( a t + 1 ) ; p r i n t f ( " lg de lp = %d, lg de dp = %d\n ", l l p, l d p ) ; r e t u r n ( l l p <= 6 4 ) && ( l d p <= ) ;

4 4 % %% \".+\" " { d o m a i n p a r t r e t u r n t e s t l g ( y y t e x t ) ; { l o c a l p a r t " { d o m a i n p a r t r e t u r n t e s t l g ( y y t e x t ) ;. p r i n t f ( " erreur lexicale \n " ) ; %% i n t main ( i n t a r g c, c h a r a r g v [ ] ) { i f ( y y l e x ( ) ) p r i n t f ( " %s: adresse correcte \n ", y y t e x t ) ; e l s e p r i n t f ( " %s: adresse incorrecte \n ", y y t e x t ) ; r e t u r n 0 ; 2 Grammaire LL(k) (6 s) On considère la grammaire : Axiome = S N = { S, A, B T = { a, b, 0, 1 P = { Grammaire G 1 S A S B A aab A 0 B abbb B 1 Questions : 1. Est-ce que la grammaire G 1 est LL(1)? G 1 n'est pas LL(1), car pour les productions de S, les ensembles directeurs ne sont pas disjoints deux à deux. PREM 1 (A SUIV 1 (S)) = {a PREM 1 (B SUIV 1 (S)) = {a 2. Pouvez-vous construire un automate à pile déterministe qui reconnaisse le langage produit par G 1? Non, pour les automates descendants, on ne peut trouver un k permettant de savoir si on prend la production A aab ou B abbb.

5 5 3 Analyse en descente récursive (7 s) BBCode 2 est une simplication du langage HTML utilisée pour mettre en forme les messages dans les forums de discussion. Le nom d'une balise est délimité par les crochets []. Certaines balises ont un attribut, dont la valeur est donnée à l'aide du symbole =. Quelques exemples : [b]texte[/b] [i]texte[/i] [color=red]texte[/color]. texte en gras texte en italique texte en rouge. Question : Écrivez un programme en pseudo-langage an qu'il transcrive un texte contenant du BBCode en un texte en LATEX. On se limitera aux balises données en exemple. Le texte à transcrire est lu sur l'entrée standard, et le texte nal est écrit sur la sortie standard. Rappels : En LATEX, \textbf{texte en gras, \textit{texte en italique, \textcolor{couleur{texte en couleur. Voici une grammaire LL(1) du langage à reconnaître : S BBCode BBCode [ b ] BBCode [ / b ] BBCode [ i ] BBCode [ / i ] BBCode [ c o l o r=r e d ] BBCode [ / c o l o r ] BBCode t e x t e S a n s B a l i s e BBCode BBCode ν Il sut ensuite d'écrire un analyseur en descente récursive, et de mettre les actions au bon endroit pour que les balises [b] soient transcrites en \textbf{, etc Bulletin Board Code.