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Try Clojure

try-clojure.org

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Re: Try Clojure

#51

Post by [deleted] »

geocar wrote: post #49
Avshalom wrote: post #47

This isn't really a Clojure specific question but is there any benefit to making 'if' a special form? Meaning you can't do: (map if [true false true] [1 1 1] [2 2 2]) not that I can think of any reason why you'd want to do that (specifically) but Picolisp, Factor, REBOL and I'm sure a couple other languages implement if as a normal function. To take an example from some edition of programming clojure: (defmacro unles…

Making "if" a special form means that it can short-circuit, and I'd rather write (if x big_expensive_expression y) than (funcall (if x (lambda () big_expensive_expression) (lambda () y)))

[deleted]

Re: Try Clojure

#52

Post by gecko »

geocar wrote: post #49
Avshalom wrote: post #47

This isn't really a Clojure specific question but is there any benefit to making 'if' a special form? Meaning you can't do: (map if [true false true] [1 1 1] [2 2 2]) not that I can think of any reason why you'd want to do that (specifically) but Picolisp, Factor, REBOL and I'm sure a couple other languages implement if as a normal function. To take an example from some edition of programming clojure: (defmacro unles…

Making "if" a special form means that it can short-circuit, and I'd rather write (if x big_expensive_expression y) than (funcall (if x (lambda () big_expensive_expression) (lambda () y)))

You mind it mostly because the Lisp funcall/lambda syntax is complex. Contrast with Smalltalk, which lacks special forms, and does use lambdas to get short circuiting:

    someBoolean ifTrue: [ 'it was true' ] ifFalse: [ 'it was false' ]
Brackets introduce lambdas. I don't find this syntax clunky, and while I've never wanted to map ifTrue:/ifFalse: before, it's nice to be able to write your own special-form-like operators this way.

Re: Try Clojure

#53

Post by [deleted] »

[deleted] wrote: post #51
geocar wrote: post #49

Earlier quoted context omitted.

Making "if" a special form means that it can short-circuit, and I'd rather write (if x big_expensive_expression y) than (funcall (if x (lambda () big_expensive_expression) (lambda () y)))

[deleted]

[deleted]

Re: Try Clojure

#54

Post by geocar »

[deleted] wrote: post #51
geocar wrote: post #49

Earlier quoted context omitted.

Making "if" a special form means that it can short-circuit, and I'd rather write (if x big_expensive_expression y) than (funcall (if x (lambda () big_expensive_expression) (lambda () y)))

[deleted]

Are you familiar with python? Perhaps this will help:

    if cnd:
      return do_big_stuff
    else:
      return do_other_big_stuff
has different semantics than a hypothetical "if" function call:

    def a():
      return do_big_stuff
    def b():
      return do_other_big_stuff
    return if(cnd,a(),b())
Note here, both "do_big_stuff" and "do_other_big_stuff" are evaluated, regardless of the value of "cond".

A short-circuiting if (only possible if "if" is a special form) will ONLY evaluate a() (and thus "do_big_stuff") if "cond" returns a truth-value.

Now, Factor's "if" works like this (in python):

    return if(cnd,a,b)()
That's fine- and it still has the short-circuiting semantics, but there's still a question of taste here.

Re: Try Clojure

#55

Post by geocar »

gecko wrote: post #52
geocar wrote: post #49

Earlier quoted context omitted.

Making "if" a special form means that it can short-circuit, and I'd rather write (if x big_expensive_expression y) than (funcall (if x (lambda () big_expensive_expression) (lambda () y)))

You mind it mostly because the Lisp funcall/lambda syntax is complex. Contrast with Smalltalk, which lacks special forms, and does use lambdas to get short circuiting: someBoolean ifTrue: [ 'it was true' ] ifFalse: [ 'it was false' ] Brackets introduce lambdas. I don't find this syntax clunky, and while I've never wanted to map ifTrue:/ifFalse: before, it's nice to be able to write your own special-form-like operator…

Factor and Ruby do the same thing. I agree that there's definitely value in having dedicated closure syntax.

Re: Try Clojure

#56

Post by ggruschow »

Rayne wrote: post #35
ggruschow wrote: post #13

Nice work. Assuming you're trying to advocate Clojure, I'd recommend changing your tutorial to make things look easy (as opposed to highlighting gotchas). I recommend doing math examples first. Show how it makes a good calculator, but avoid discussion of ratios. That's (unnecessarily) confusing.. just like everything in the hello world example starting from the nil output on. By the time I got to the sequence page, I…

I don't know if you noticed, but I tried to be very explicit about the fact that the tutorial is nowhere near finished. I wrote that up in 1 hour yesterday. I'm well aware that it needs filling in with less difficult stuff. I intend to start serious work on it today. Also, I'm trying to get Michael Fogus (author of Joy of Clojure) to write the tutorial. If he decides to do so, I can almost promise you quality. ;)

I just meant to be offering constructive feedback. The tutorial was useful for me. It's certainly way better than the tutorial I had before you wrote it! It's pretty impressive for an hour of work.

Re: Try Clojure

#57

Post by stonemetal »

Avshalom wrote: post #50
Rayne wrote: post #48

Earlier quoted context omitted.

Well, it's actually impossible to write if as a function in Clojure.

I think it's impossible to write if as a function in anything, I'm pretty sure that at some point you need a branching primitive, but the if the VM uses and the if exposed to the user don't have to be the same thing. Like I said though, it's not a Clojure specific question, CL and Scheme both use a special form for if as well. Even if it can't be done in a JVM language it can be done. I'm just curious if there's any…

The first problem you run into is call by value. As a function the args to if would be evaluated before the function call. You could force the user to quote the branches to the if call to get around it but the special form is less error prone.

Re: Try Clojure

#58

Post by Avshalom »

geocar wrote: post #54
[deleted] wrote: post #51

Earlier quoted context omitted.

[deleted]

Are you familiar with python? Perhaps this will help: if cnd: return do_big_stuff else: return do_other_big_stuff has different semantics than a hypothetical "if" function call: def a(): return do_big_stuff def b(): return do_other_big_stuff return if(cnd,a(),b()) Note here, both "do_big_stuff" and "do_other_big_stuff" are evaluated, regardless of the value of "cond". A short-circuiting if (only possible if "if" is a…

Yeah okay I got it. I think the funcall/lambda stuff got me confused, it's kind of obvious in hindsight.

In which case I agree it's a matter of taste. I guess I just like the taste of Factor/REBOL always passing blocks to if, having to say t [ 0 ] [ 3 ] if instead of simply say t 0 3 if is the trade off I suppose[1].

I'm guessing it works for picolisp because it's purely interpreted? because it certainly doesn't seem to be passing lambdas to 'if'. Can anyone confirm/deny?

[1]well actually the word ? does that but to make it work for both you need to do:

: myif ( ? true false -- ) ? dup quotation? [ call ] [ ] if ; inline

Re: Try Clojure

#59

Post by anonymousDan »

geocar wrote: post #49
Avshalom wrote: post #47

This isn't really a Clojure specific question but is there any benefit to making 'if' a special form? Meaning you can't do: (map if [true false true] [1 1 1] [2 2 2]) not that I can think of any reason why you'd want to do that (specifically) but Picolisp, Factor, REBOL and I'm sure a couple other languages implement if as a normal function. To take an example from some edition of programming clojure: (defmacro unles…

Making "if" a special form means that it can short-circuit, and I'd rather write (if x big_expensive_expression y) than (funcall (if x (lambda () big_expensive_expression) (lambda () y)))

What about for lazy languages such as Haskell? I guess you get short circuiting by default there no?

Re: Try Clojure

#60

Post by Rayne »

ggruschow wrote: post #56
Rayne wrote: post #35

Earlier quoted context omitted.

I don't know if you noticed, but I tried to be very explicit about the fact that the tutorial is nowhere near finished. I wrote that up in 1 hour yesterday. I'm well aware that it needs filling in with less difficult stuff. I intend to start serious work on it today. Also, I'm trying to get Michael Fogus (author of Joy of Clojure) to write the tutorial. If he decides to do so, I can almost promise you quality. ;)

I just meant to be offering constructive feedback. The tutorial was useful for me. It's certainly way better than the tutorial I had before you wrote it! It's pretty impressive for an hour of work.

I appreciate the feedback! I didn't take any offense to what you said. :)

I'm not entirely certain I'm qualified to write a Clojure tutorial anyway, which is why I hope Michael is interested.

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