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 > <javascript:>> 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.
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