Arc Forum | i think it's the fact that those concerns don't occur in the language to begin w...

Arc Forum

4 points by tokipin 5943 days ago | link | parent

i think it's the fact that those concerns don't occur in the language to begin with. from what i glanced (i can't find the pdf anymore,) the interpreter switches between different representations depending on how the particular table is used, and can switch between the representations dynamically for the given table (i'm not sure if the switching is bidirectional)

but the user never sees any of that. if you want an array or tuple you type

  local blah = { 1, "two", function return 3 end }

if you want a hash table you type

  local blah = { bleh = "yep", bleagh = "whatever" }

  -- both of the following are valid
  print( blah["bleh"] )
  print( blah.bleh )

sparse array:

  local blah = { "my", "name", "is", [12] = "slim", [888] = "shady" }

hybrid:

  local blah = { "element 1", "element 2", name = "son", lastname = "goku" }

nesting:

  local blah = { { "star", "bucks" }, { "apple", "sauce" } }

etc:

  local blah = { [{ 1, 3, 5 }] = "odd", [{ 2, 4 }] = "even" }

basically, any sequency, key-valuey, or structured ish thingie, i can just write out without worrying about anything. i'm sure it's doin' some sort 'o magic under the hood, but to that end they could be sacrificing lawn gnomes for all i care

and keep in mind that Lua is likely the fastest interpreted language... or at least it was before the Javascript optimization race started. i think one of the Javascript engines has features inspired by the Lua VM

and then there's metatables, which are properties that can be set to control the behavior of values in different situations. for example, one of the properties is __index, which is referred to when a table doesn't have a value for a given key. this enables straightforward memoization, inheritance, hidden data management, infinite data structures, etc

other metatable properties determine the operation of the value under addition, comparison, etc

you could, for example, implement complex numbers as if they were part of the language, simply by creating a seed table called i. when an expression such as 1 + 2 * i is reached, the __mul property would perform the complex multiplication, then return a new Complex table which would in turn perform the addition. along each step it would be a normal table, so you could do, for example:

  print( (1 + 2 * i).polar_form )

keeping in mind that the table access is dynamic, hence polar_form can be calculated each time it's accessed, no need for getting/setting. also, this:

  print( 8 * i^5 + 2 * i )

would work as it should because there's a __tostring property

i've been thinking of making an APL-like DSL (would be nice to be able to implicitly map and whatnot) in this sort of manner. i haven't looked deep into Ruby but i believe it has things of this nature

here's a description of metatables:

http://www.lua.org/manual/5.1/manual.html#2.8

the fact that tables are used everywhere is unoverstatable. environments are tables, therefore you can do powerful things with environments. like writing your own import/include function, reading and writing global state in a file, anaphora and implicits... pretty much a bunch of crazy shit

along with this some very well-chosen features such as coroutines, closures, the implementation of most language features as modules (eg file.open, coroutine.wrap) to keep the syntax clean, etc

the tables by themselves go a long way, especially with their It Just Works® all-purpose syntax. but the way this flexibility is encouraged through the rest of the language makes it a wonderful unified package