CS 405/505 ASSIGNMENT #2
Due Wednesday, January 31, 2007
Consider the following extended BNF grammar for a subset of the Perl programming language,
called MicroPerl.
program ::= use strict ;
require “list.pl” ;
{sub-definition }
{ { declaration ;}{statement } }
sub-definition ::= sub sub-identifier {
my variable-identifier = @ ;
{declaration ;}{statement }
return ( expression ) ;
}
declaration ::= my variable-identifier
statement ::= variable-identifier = expression ;
|if ( expression )statement-block [else statement-block ]
|while ( expression )statement-block
|print variable-identifier ;
statement-block ::= {statement {statement } }
expression ::= term |expression binary-op expression
term ::= primary-expression |unary-op term
primary-expression ::= variable-identifier |integer |list-expression
|sub-identifier list-expression
|hd list-expression
|tl list-expression
|isNil list-expression
list-expression ::= ([ expression {,expression }])
Syntactic and Semantic Conventions The keywords and the token symbols in MicroPerl
are in bold. Note that MicroPerl has symbols {and }, which are distinguished from grammar
metasymbols {and }, respectively, by underlining. The unary operators are +, −and ! (negation)
Binary operators obey the customary precedence rules, from highest to lowest:
multiplicative ∗, /
binary additive +,−
relational ==, ! =, <,>,<=, >=
boolean &&, k
A MicroPerl sub identifier is a bare name, which consists of letters (only alphabetic characters),
digits, and underscores ( ) with the restrictions that it must begin with a letter, cannot end with
an underscore and cannot have two consecutive underscores. For example, give 2 Joe, tell me and
A45Asm3 are valid bare names, but 6gh, two bad, and no end are not. A MicroPerl variable may
be a scalar variable or a list variable. A scalar variable identifier begins with a $, followed by a bare
name. A list variable identifier begins with a @, followed by a bare name. integer is an unsigned
integer. MicroPerl comments are indicated by being preceded by # and terminated by the end of
the line.
