Question

Consider the following context free grammar. Write an attribute grammar that specifies the calculation rules, i.e. how the value of E or T is calculated. There is no need to perform type checking. We assume all types are matched correctly. Please clearly specify the type of attribute(s) you introduce, i.e. synthesized, inherited, or intrinsic. E ::= E + T | T T ::= T * F | F F ::= NUM NUM ::= 1 | 2 | 3 | 4 | 5

Answer 1

Answer : Given Context free grammar is E ::= E + T | T T ::= T * F | F F ::= NUM NUM ::= 1 | 2 | 3 | 4 | 5

                  Grammars with attributes stored at each node is called attribute grammar.

                   Productions                       Attribute Grammar

                   E ::= E₁ + T                     E.val = E₁ .val + T . val

   E ::= T                                  E.val = T . val

                   T ::= T * F                             T.val = T₁ .val * F . val

                   T ::= F                                   T.val = F . val

                   F ::= NUM                             F.val = NUM.val

                   NUM ::= 1                             NUM.lexval = 1

                   NUM ::= 2                              NUM.lexval = 2

                   NUM ::= 3                              NUM.lexval = 3

                   NUM ::= 4                               NUM.lexval = 4

                   NUM ::= 5                              NUM.lexval = 5

                   Synthesized attributes are those computed from children. Inherited attributes computed from sibling or

                   parent.

                 Here all attributes 'val' are synthesized as its computed from child nodes attribute.

                 For example   in , E.val = E₁ .val + T . val

                 To compute value of E , we need to compute value of E₁ and value of T..

                 NUM.lexval is intrinsic attribute.

                Here there is no inherited attribute.