Some fast answers/hints on Problems in chapter 3

Problem 2. Probably the quickest way of finding reliable syntax
for common languages like Pascal and C i3 to use my lookup320
program on the WWW:
http://www.csci.csusb.edu/cgi-bin/dick/lookup320
and type in patterns like
	pascal.*proce
and select the relevant link.

A "procedure call statement"in the book is officially described as a
	procedure statement

Similarly my syntax for C has no switch_statement but it
does have a selection_statement.  A float leteral is listed as a float constant...

Another approach is to find the complete syntax description and use
your browser's "Search in page" menu item.

Problem 5.  Needs a "for instance" of ambiguity....so
	Draw TWO trees for one sentence.  No waffle!


Problem 7.  You can rewrite the grammar in English, but if you
think a bit more you can describe the whole language in
a single phrase:
	"one or more 'a's followed by one or more 'b's followed by
	 one or more 'c's"

Problem 10. This needs you to either know or create a trick....
it is tempting to start
	S ::= A B,
but if you do, you loose control over the number  of 'a's in A
and the number of 'b's in B.  You need to back out of this obvious
blind alley and think of a different way of looking at the language:
Look at the incomplete list below:
	   ab
	  aabb
	 aaabbb
	aaaabbbb
Does it suggest a different pattern to you?

If not look at this:
		ab
	      a ab b        = aabb
	    a  aabb b       = aaabbb
	  a   aaabbb  b     = ???
Does that give you a different structure for { a^n b^n | n>0}?

If not here is a clue:

It is a single BNF statement like this:

	S ::= ?? | ? S ? .

Problem 12.  There won't be any Pascal in the final, but
could you do the virtual semantics for the equivalent C/C++
	a. do-while
	b. for(i=start; i>=stop; i--)S
?

Problem 13 is actually a simple exercise in algebra....
	substitute a=2*(b-1)-1 in {a>0} to get {2*(b-1)-1>0}
		and simplify.

Problem 14 is slightly harder.  Two steps.  Work BACKWARDS.

Problem 15.  Very tough.... in fact I'd only set this in the 600
level programming language class final. :-)