CS 541 Lecture -*- Outline -*-

* Judging programming language designs

     goal: explore the questions:
     	When is one language better than another?
	How to formalize that?

** Flon's axiom: can write bad programs in any language
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              FLON'S AXIOM
 (SIGPLAN Notices, 10(10):16-17, Oct 1975)

"There does not now, nor will there ever,
exist a programming language in which it
is the least bit hard to write
bad programs."
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        Q: Do you believe that?
        Q: What are some examples of good features that can be abused?
        Q: So what do we really care about?

** The paradox of judgement
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        THE PARADOX OF JUDGEMENT

  - all languages Turing-complete
       (Turing tarpit, Church equivalence)

  - all constructs can be abused

  - so how can one formally:
      compare languages,
      evaluate them, and
      make judgements?
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	Answers: evaluate them on specific tasks (what they can do)
			--> problem: how to formalize, what tasks?
		other metrics (e.g., principles)
			--> principles
		restrict the translations
			--> Felleisen's homomorphic translation approach

***	MacLennan's principles of language design
		from his book "Principles of Programming Languages"
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 MACLENNAN'S PRINCIPLES OF LANGUAGE DESIGN
    (Principles of Programming Languages,
     Holt, Rinehart and Winston, 1987)
 
Expressiveness:

   - abstraction,
   - automation,
   - information hiding,
   - allowing expression of security,
   - structure or readability,
   - meta-linguistic abstraction

Efficiency:

   - programming time,
   - compile-time,
   - run-time,
   - object file size,
   - run-time space,
   - localized costs,
   - portability

Aesthetics:

   - simplicity,
   - syntactic consistency,
   - orthogonality,
   - regularity,
   - zero-one-infinity,
   - terseness or syntactic abstraction 
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    Q: how to formalize expressiveness and aesthetics?