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I wish Julia the best after 7 years of having to use Matlab, but despite its metaprogramming facilities, it's not actually homoiconic. It appears enough people

by KingMob 10y ago

I wish Julia the best after 7 years of having to use Matlab, but despite its metaprogramming facilities, it's not actually homoiconic. It appears enough people pointed this out that they finally stopped using the word on their website.

leephillips 10y ago
"Like Lisp, Julia represents its own code as a data structure of the language itself. Since code is represented by objects that can be created and manipulated from within the language, it is possible for a program to transform and generate its own code. This allows sophisticated code generation without extra build steps, and also allows true Lisp-style macros operating at the level of abstract syntax trees." (http://docs.julialang.org/en/stable/manual/metaprogramming/#macros http://docs.julialang.org/en/stable/manual/metaprogramming/#...) Doesn't this qualify? I may certainly be missing something in my understanding of what "homoiconic" means.
- KingMob 10y ago
  Homoiconic means that the code structure is similar to the actual AST. In Lisps, this is easy to see, because a nested list of symbols is pretty much the definition of an AST. In truth, real homoiconicity is hard to achieve in any language that doesn't represent code as trees/S-expressions. In Julia, they built a data structure that can represent code, and can be accessed via reflection, but it's no more homoiconic than most languages (note that "homoiconic" is nowhere on the page you linked to). In Lisps, the code is just nested lists, like other list data, and can be manipulated using the all of the standard list-processing functions. Whereas, if you look at the examples in Julia, you'll see that using macros vs functions involves special syntax all over the place. A good page for this is http://c2.com/cgi/wiki?HomoiconicLanguages http://c2.com/cgi/wiki?HomoiconicLanguages
  - leephillips 10y ago
    I see - you're exactly right. Thanks for the clear explanation.
  - KenoFischer 10y ago
    Usually I avoid splitting hairs, but since the terminology bikeshed is all about that, let me make a little correction. In julia, there is a data structure called `Expr`, which is what's used internally by the compiler to represent code and is exposed to julia. It's not a list, it's a tree, but the power of being able to access it like any other tree still remains. Of course julia's surface syntax is significantly more complicated than lisp, so macros are more complicated.

by KingMob 10y ago

leephillips 10y ago

"Like Lisp, Julia represents its own code as a data structure of the language itself. Since code is represented by objects that can be created and manipulated from within the language, it is possible for a program to transform and generate its own code. This allows sophisticated code generation without extra build steps, and also allows true Lisp-style macros operating at the level of abstract syntax trees." (http://docs.julialang.org/en/stable/manual/metaprogramming/#macros http://docs.julialang.org/en/stable/manual/metaprogramming/#...) Doesn't this qualify? I may certainly be missing something in my understanding of what "homoiconic" means.

KingMob 10y ago
Homoiconic means that the code structure is similar to the actual AST. In Lisps, this is easy to see, because a nested list of symbols is pretty much the definition of an AST. In truth, real homoiconicity is hard to achieve in any language that doesn't represent code as trees/S-expressions. In Julia, they built a data structure that can represent code, and can be accessed via reflection, but it's no more homoiconic than most languages (note that "homoiconic" is nowhere on the page you linked to). In Lisps, the code is just nested lists, like other list data, and can be manipulated using the all of the standard list-processing functions. Whereas, if you look at the examples in Julia, you'll see that using macros vs functions involves special syntax all over the place. A good page for this is http://c2.com/cgi/wiki?HomoiconicLanguages http://c2.com/cgi/wiki?HomoiconicLanguages
- leephillips 10y ago
  I see - you're exactly right. Thanks for the clear explanation.
- KenoFischer 10y ago
  Usually I avoid splitting hairs, but since the terminology bikeshed is all about that, let me make a little correction. In julia, there is a data structure called `Expr`, which is what's used internally by the compiler to represent code and is exposed to julia. It's not a list, it's a tree, but the power of being able to access it like any other tree still remains. Of course julia's surface syntax is significantly more complicated than lisp, so macros are more complicated.