grading criteria of hw4

From: Rui Shi (shearer@cs.bu.edu)
Date: Thu Oct 19 2006 - 12:47:40 EDT 

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From: "Rui Shi" <shearer@cs.bu.edu>
To: "'cs520 Course Account'" <cs520@cs.bu.edu>
Subject: grading criteria of hw4
Date: Thu, 19 Oct 2006 12:47:40 -0400
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Hi all,
 
Here is the grading criteria of hw4.
 
Thanks,
 
Rui
 
============================================================================
=============================================================
Grading Criteria
 
 1. (T-Abs-Wild) 4 pt, (E-AppAbs-Wild) 3 pt. Proof: derivability of typing
rule has to use weakening of \Gamma (4 pt), and evaluation rule has to
mention x \notin fv(t12) so [x |-> t2] t12 = t12 (4 pt).
 
 2. violates call-by-value (2 pt). does not preserve ill-typedness (3 pt).
 
 3. if t0 then t1 else t2 (2 pt); true, false, Bool (1 pt ea).
 
 4. equal (2 pt); plus, times, factorial (1 pt ea).
 
 5. part (1): type system guarantees that S = T in the evaluation rules
mentioned for well-typed programs (5 pt); part (2): more ill-typed programs
are now stuck (5 pt). Extra credit: 5 pts for showing typing derivation of t
and t' for some t -> t' with these evaluation rules; 5 pts for observing
that head[T] nil[T] and tail[T] nil[T] get stuck, but they're well-typed
programs.
 
Grades break down:
 
(1) 15 pts, (2) 5 pts, (3) 5 pts, (4) 5 pts, (5) 10 pts + 10 extra.
 
total: 40 pts + 10 extra
 
 

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