On Monday, March 11, 2019 at 1:13:30 PM UTC-4, Brian Adkins wrote:
>
>
>
> On Monday, March 11, 2019 at 12:29:40 PM UTC-4, Matthias Felleisen wrote:
>>
>>
>>
>> > On Mar 11, 2019, at 11:21 AM, Brian Adkins <lojic...@gmail.com> wrote: 
>> > 
>> > I just discovered that define will fail at runtime, where let would 
>> fail at compile time. Besides helping to keep the indentation level from 
>> marching to the right "too much", what are the benefits of define over let? 
>> > 
>> > --- snip --- 
>> > #lang racket 
>> > 
>> > (define (f n) (+ n 1)) 
>> > 
>> > (define (foo) 
>> >   (define b (f a)) 
>> >   (define a 7) 
>> >   
>> >   b) 
>> > 
>> > (define (bar) 
>> >   (let ([b (f a)] 
>> >         [a 7]) 
>> > 
>> >     b)) 
>> > --- snip --- 
>>
>>
>>
>> I think your characterization is a bit misleading here. 
>>
>> In ‘bar’ ‘a’ is not bound, something that Racket (and DrRacket) properly 
>> signal at compile time. 
>>
>> In ‘foo’ ‘a’ *is* bound, because you’ve set up a mutually recursive 
>> scope. But, when Racket evaluates (foo) it notices that ‘a’ is bound but 
>> uninitialized, which is two different things. 
>>
>> If you want to compare apples to apples, use a ‘letrec' instead of a 
>> ‘let' in ‘bar'. Then you have (1) the same semantics and (2) the same 
>> error. 
>>
>> — Matthias 
>>
>>
> I want let semantics, but I've been using define more because it's 
> preferred in the Racket style guide. I don't want the behavior of define 
> above, so using letrec to get a runtime error instead of compile time error 
> doesn't make sense.
>

Oops - I should've used let* in my example. 

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