Hi Mike: it looks to me like you have the right definition in the sense that it relates the right terms to each other. The rest of the exercise is just to get you to use Redex's `with` to express it and to avoid using the name `E` for a non-evaluation context. These are very minor things! What's being asked is that you use the name `C` for the compatible closure context (not change `E` like you've done) and then use `with` in the reduction relation definition to lift the axioms to arbitrary contexts. You would also not call this new (racket-level) definition `iswim-standard` (since it isn't the standard reduction).
Robby On Fri, Nov 29, 2019 at 12:47 PM Mike MacHenry <mike.mache...@gmail.com> wrote: > > Hey everyone, > > I am a little confused about Exercise 12.6 from Semantics Engineering with > PLT-Redex. The exercise is as follows: > > "Formulate a general reduction relation for ISWIM using a with clause. Use > traces to demonstrate that programs may be reduced to values along several > different paths in a reduction graph. " > > The problem I'm having with this is that to accomplish this goal, I needed to > make a change to the ISWIM language definition on page 217 at the beginning > of this chapter, particularly in the contexts section, and I made absolutely > no change to the reduction relation given on page 225 directly above this > exercise. > > So for me, that language definition from 217, along with the reduction > relation on 225, as well as the definitions for the meta functions in this > chapter, I get the standard reduction, which permits only one reduction path > for, say, an expression like (+ (1 1) (+ 1 1)). The left-most (+ 1 1) reduces > to 2 first. > > When I make the change to the contexts in the language definition, and change > it from > > (E hole (V E) (E M) (o V ... E M ...)) > > to > > (E hole (M E) (E M) (o M ... E M ...)) > > My traces for the above expression gives what I think the exercise is > expecting. I have a diamond shaped in my reduction DAG. > > The problem I have with this is that I haven't done anything to the reduction > relation to do this. The exercise seems pretty explicit to create a reduction > relation using a with clause. so it seems like the purpose of the exercise is > to get you to understand the with clause by developing something new using > it. Now granted my reduction relation does use a with clause, because it's > the one I copied out of the book. But I didn't write that one and use the > with clause in my own new way. > > So is there a different way to get the reduction relation to support the > general reduction that requires one to change the reduction relation and not > the grammar? > > Thanks for the help, > -mike > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/CAAzRdbcM9w9wi-mPzdpY_4tBWSWv_QaXvZDpgNiXSEr05OaMoA%40mail.gmail.com. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAL3TdOOziqT5365jtknP8N9pJAA-UJiLTVZi12oEXSofGgjkgg%40mail.gmail.com.
