the operand types are not the same is always real. When they are the same, the EXAMPLE $3\mathrm{.}2$

A Grammar for Simple Assignment Statements

$=$

$AB|C$

$+$

$*$

$|()$

The grammar of Example $3\mathrm{.}2$ describes assignment statements whose right

sides are arithmetic expressions with multiplication and addition operators and

parentheses. For example, the statement

$A=B*(A+C)$

is generated by the leftmost derivation:

$$ assign

$=>A=$

$=>A=B*$

$=>A=B*()$

$=>A=B*(+)$

$=>A=B*(A+)$

$=>A=B*(A+)$

$=>A=B*(A+C)$ Write an attribute grammar whose base BNF is that of Example $3\mathrm{.}2$ and

whose type rules are the same as for the assignment statement example

of Section $3\mathrm{.}4\mathrm{.}5.$

expression type is that of the operands. The type of the left side of the assign$-$

ment must match the type of the right side. So the types of operands in the

right side can be mixed, but the assignment is valid only if the target and the

value resulting from evaluating the right side have the same type. The attribute

grammar specifies these static semantic rules.

The syntax pertion of our example attribute grammar is

$=$

$+$

$|$

$A|B|C$

The attributes for the nonterminals in the example attribute grammar are

described in the following paragraphs:

actual$\_$type$-$A synthesized attribute associated with the nonterminals Syntax rule: procedure $[1]$

end $[2]$;

Predicate: $[1]$ string $==<mtext></mtext><mi>p</mi><mi>r</mi><mi>o</mi><msub><mrow><mi>c</mi></mrow><mrow><mi>n</mi></mrow></msub>$ame $>[2].$ string