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> cons-cell is a terrible abstraction on modern hardware Could you expand on this? Also, whether or not it's better to teach to kids than JavaScript, Squirrel

> cons-cell is a terrible abstraction on modern hardware Could you expand on this? Also, whether or not it's better to teach to kids than JavaScript, Squirrel is a more traditional curly-brace alternative to Lua for embedded development.

bsder 13y ago
> > cons-cell is a terrible abstraction on modern hardware > Could you expand on this? Sure, that one is pretty easy. cons cells are effectively 2 pointers. Consequently, they are not guaranteed nor expected to be near one another in memory. Now, that's not a big deal with respect to the first pointer. That contains the thing, so we always have to chase that down. In a Lisp/Scheme cons-cell list, the second pointer needs to be referenced to get to the next cons cell. So, we have to chase a second pointer just to move to the next element. Every time you chase a non-contiguous pointer like this, the processor may have to bring in a cache line and that's a big penalty. Contrast this to say, an array/vector. To get to the next element you just add some small amount to the current index. It's likely already in the same cache line as the previous element. Arrays/vectors have a big win over pointer-based lists in terms of locality of reference on a modern microprocessor. There is a second problem with cons cells in that their abstraction in terms of the language also has problems: "Programing Language: Why Lisp Do Not Have a Generic Copy-List Function" http://xahlee.info/UnixResource_dir/writ/lisp_equal_copy_list.html http://xahlee.info/UnixResource_dir/writ/lisp_equal_copy_lis... http://www.nhplace.com/kent/PS/EQUAL.html http://www.nhplace.com/kent/PS/EQUAL.html
bsder 13y ago
What is so much better between Squirrel and Javascript? To my eye, they look pretty much the same. And Javascript has an enormous ecosystem. While Squirrel has a very small niche of the not terribly large Lua ecosystem. This isn't to knock Squirrel as a language, but I view this in the same light and Python vs. Ruby. The languages don't have enough better/different from one another for me to tell someone to switch if they already know one or the other.

bsder 13y ago

> > cons-cell is a terrible abstraction on modern hardware > Could you expand on this? Sure, that one is pretty easy. cons cells are effectively 2 pointers. Consequently, they are not guaranteed nor expected to be near one another in memory. Now, that's not a big deal with respect to the first pointer. That contains the thing, so we always have to chase that down. In a Lisp/Scheme cons-cell list, the second pointer needs to be referenced to get to the next cons cell. So, we have to chase a second pointer just to move to the next element. Every time you chase a non-contiguous pointer like this, the processor may have to bring in a cache line and that's a big penalty. Contrast this to say, an array/vector. To get to the next element you just add some small amount to the current index. It's likely already in the same cache line as the previous element. Arrays/vectors have a big win over pointer-based lists in terms of locality of reference on a modern microprocessor. There is a second problem with cons cells in that their abstraction in terms of the language also has problems: "Programing Language: Why Lisp Do Not Have a Generic Copy-List Function" http://xahlee.info/UnixResource_dir/writ/lisp_equal_copy_list.html http://xahlee.info/UnixResource_dir/writ/lisp_equal_copy_lis... http://www.nhplace.com/kent/PS/EQUAL.html http://www.nhplace.com/kent/PS/EQUAL.html

bsder 13y ago

What is so much better between Squirrel and Javascript? To my eye, they look pretty much the same. And Javascript has an enormous ecosystem. While Squirrel has a very small niche of the not terribly large Lua ecosystem. This isn't to knock Squirrel as a language, but I view this in the same light and Python vs. Ruby. The languages don't have enough better/different from one another for me to tell someone to switch if they already know one or the other.