Programming Languages (CS302 2006S)

Notes on the Syntax of Scheme (R5RS 7.1)

Comments on:

Kelsey, R., Clinger, W., and Rees, J. (Eds). (1998). Revised5 Report on the Algorithmic Language Scheme. Section 7.1

Comments from: Peter Brown, Michael Claveria, Davis Hart, Alex Leach (*), Brad Miller, Angeline Namai, Mark Nettling, Dave Ventresca (late).

No Comments from: Dimitar Tasev (x).

I was unable to make much sense of section 7 beyond what I already understand Scheme's syntax, maybe its just my brain being fried right now, but I feel like I should have been able to get more out of it, but its not coming.

I think I understood most of 7.1.1 except for the number representations (The @ sign in the def for <complex R> for example, was confusing) 7.1.3 was less clear to me, specifically the section on <derived expression>'s I have no idea what the <macro block> at the end of section 7.1.3 is talking about. I would also appreciate some guidance on section 7.1.4

Can you go over the scheme representation of complex numbers. The rest of the reading was basically just a grammar of lefthand->righthand rules for scheme and mostly fit to my understanding of the language.

I actually found this reading more enjoyable than I thought I might because we are going over context-free languages right now in CSC 341. It's neat to see the theory put into practice in designing a language. The sections on Quasiquotations was a little unclear to me though. Where exactly do quasiquotations fit into the "scheme" of things? The auxillary functions were a little dense, are they describing functions syntatically/mathematically, essentially?

In the expression <number> -> <num 2> | <num 8> | <num 10> | <num 16>, what is the significance of the integers 2,8,10 and 16? I know that binary, octal, hexidecimal and decimal numerical notation is conventional, but why not have 4 or 32?

What is <ellipsis> -> <the identifier..> in section 7.1.5? What does any of those symbols on page 41 mean? My head hurts just looking at them. Could you go over one of those little sections so I could maybe understand a little.

The Scheme grammar looks similar to all of the other one grammar I have ever seen before - that one being for Rebelsky's STUPID language. I was surprised to see such informal rules like <comment> -> ;<a; subsequent characters up to a line break> which, while clear in their meaning, omit some of the formalism I expected to see in a grammar. I am also interested by the fact that the designers included a number of the built-in procedure names such as 'set!'. I expected to see control structures such as conditionals, but not procedures which do not have special format or significance, like 'set!'.

The reading was pretty straightforward. One thing I noticed is that it had real, unsigned real, and unsigned int, but there was no signed int. Is there a reason for this? Also, if sequence is just 0 or more instances of command followed by an expression, and command is just an expression, why isn't sequence just defined by expression*? Or command*? Does <statement>* just imply that the statements are the same, since <statement> could imply any of many different things?


I don't really understand how the quasiquotation syntax works. I think I understand _what_ quasiquoting is but the syntax is confusing.

Why are there #'s in the numbers rules?

I am not sure what comments to give, especially since the section is mainly about grammar rules. It's like trying to explain the reason behind the structure of a spoken language such as English. I suppose Scheme's syntax supports as many grammar rules as possible in order to provide a solution to computable programming problems. However, even after reading this section, I do not understand why we are required to take a course in formal languages. Some claim that a grammar is useful for those who are trying to learn the syntax of a language, but Grinnell CS majors learn the syntax of three languages with no profound understanding of grammars. Aside from linguists, theoreticians, and the designers of compilers and interpreters, I wonder whether any programmers apply most of what they have learnt from a course like CS341. Aren't there other branches of computing that do not require a semester's-worth knowledge of formal languages and grammars? I guess I am puzzled as to why CS341 is a core requirement for the major. Then again, I may not have clearly understood the power of formal languages.

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Samuel A. Rebelsky,