Re: [racket-users] Confused about Semantics Engineering Exercise 12.6

[Mike MacHenry]

Also this is a *very* minor point, but I'm pretty sure exercise 13.2 should
read "Compare with the full grammar from exercise 12.2." rather than to
compare with 12.1. Maybe not worthy even of the errata page. I don't know.
But if you're going to reprint ever it'd be nice to flag for clean up.

On Sat, Nov 30, 2019 at 3:45 PM Mike MacHenry 
wrote:

> Hm... so I guess I'm "using a with clause" like the book requests if I'm
> redeveloping the iswim-general reduction relation myself, even if the only
> difference from the book's version is to name it general and to make it
> reference the new iswim language I made that has the compatible closure
> context instead of the evaluation context. This makes more sense, thanks.
> It felt like I must have misunderstood because what I did, which was the
> quickest and easiest way to do this, was to change my original language
> definition, rather than make a new one and thus need to make a new
> reduction using a with clause.
>
> -mike
>
> On Sat, Nov 30, 2019 at 11:17 AM Robby Findler 
> wrote:
>
>> 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 
>> 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
>> .
>>
>

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Re: [racket-users] Confused about Semantics Engineering Exercise 12.6

[Mike MacHenry]

Hm... so I guess I'm "using a with clause" like the book requests if I'm
redeveloping the iswim-general reduction relation myself, even if the only
difference from the book's version is to name it general and to make it
reference the new iswim language I made that has the compatible closure
context instead of the evaluation context. This makes more sense, thanks.
It felt like I must have misunderstood because what I did, which was the
quickest and easiest way to do this, was to change my original language
definition, rather than make a new one and thus need to make a new
reduction using a with clause.

-mike

On Sat, Nov 30, 2019 at 11:17 AM Robby Findler 
wrote:

> 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 
> 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
> .
>

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[racket-users] Confused about Semantics Engineering Exercise 12.6

[Mike MacHenry]

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

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Re: [racket-users] Help understanding cond expression

[Mike MacHenry]

You need to apply the function to 'John, with a single quote in front of
it. The word John without that quote is just a variable reference to
something that you have not actually defined.

On Sat, Jan 12, 2019 at 11:34 PM Hassan Shahin  wrote:

> I have this definition for a procedure:
>
> (define type-of (lambda (item)
>  (cond
>[(pair? item) 'pair]
>[(null? item) 'empty-list]
>[(number? item) 'number]
>[(symbol? item) 'symbol]
>[else 'some-other-type])))
>
> My understanding is that if the first 4 conditions fail (=> #f
> ), then the last expression (the
> else expression) is evaluated.
> When I apply this procedure to John, as in (type-of John) I get an error
> (; john: undefined; ; cannot reference an identifier before its
> definition).
>
> What is going on?
> Thanks
>
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Re: [racket-users] Getting errors running PLT-Redex book example

[Mike MacHenry]

Thanks Ben. Good to know. Hey Robbie, it's been a while. Hope everything is
going well. Great book. :)

-mike

On Jan 12, 2019 12:04, "Robby Findler"  wrote:

Hi Mike! Thanks for pointing this out. I've updated the errata
(Thanks, Ben for those links; I was having trouble finding the date of
the change.)


Robby


On Sat, Jan 12, 2019 at 4:41 AM Mike MacHenry 
wrote:
>
> Hey everyone,
>
> I'm having an issue with one of the examples from Semantics Engineering
With PLT Redex. Specifically in 12.3 on page 225, the definition for the
iswim-standard reduction relation. As printed in the book, I get the error
"reduction-relation: shortcut name may not be a non-terminal in: M".
Following this advice I've changed the M and N on this line, both the
binding and the reference, to A and B respectively. This seems to work just
fine. Have I misunderstood something or found a typo? I checked the books
errata and didn't see any mention of it in there.
>
> Thanks a bunch,
> -mike
>
> --
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[racket-users] Getting errors running PLT-Redex book example

[Mike MacHenry]

Hey everyone,

I'm having an issue with one of the examples from Semantics Engineering 
With PLT Redex. Specifically in 12.3 on page 225, the definition for the 
iswim-standard reduction relation. As printed in the book, I get the error 
"reduction-relation: shortcut name may not be a non-terminal in: M". 
Following this advice I've changed the M and N on this line, both the 
binding and the reference, to A and B respectively. This seems to work just 
fine. Have I misunderstood something or found a typo? I checked the books 
errata and didn't see any mention of it in there.

Thanks a bunch,
-mike

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