List and Array operations

This is an attempt to collect ideas and discussion on list/array operations. NB! Below, we'll try to use "lists" as a concept covering what's sometimes called "arrays" or "vectors".

For current list comprehension functionality, see List Comprehensions

Future Ideas

Old Discussion

• concat()
  • https://github.com/openscad/openscad/issues/201
  • Vector append in RapCAD: http://www.gilesbathgate.com/2011/09/rapcad-dynamic-arrays/
  • Using comma as concatenation operator: newlist = lista, listb;
  • Use the concatenation operator from the D programming language: lista ~= listb; listc = lista ~ listb;

Ideas:

• Functional list paradigm: cons/car/cdr
• List slicing (extract subset of a list)
  • Python notation: list[a:b] (a through b-1), list[a:] (a to end), list[:b] (start to b-1), list[:] (entire list)
• Picking indices

list2 = list[2,4]; // returns [3,1] ```

• Use stack-like push / unshift

• Declare lists in the same way as ranges

  • list = [2:0.5:4]; // Returns [2,2.5,3,3.5,4]

• Support list comprehensions (map):

function double(list) = _ * 2;
list = [0,1,2,3];
list2 = double(list); // Returns [0,2,4,6]

(can already do this echo([0,1,2,3]*2); // = [0,2,4,6]

• Python-inspired syntax: [for i = [a:b] f(i)];
• Advanced recursion example:

function a(b) = length(b) > 1 ? ( sin(b[0]) * 5, a(b[1:]) : sin(b[0]) * 5;

• Random access: list = [0,1,2,3]; list[1] = 4; // Returns [0,4,2,3];

• Iteration over a vector

   foreach (i=vector) {
      ...
   }

• Various math functions would help, my max/min/sum from http://www.thingiverse.com/thing:70745 for example, it would have been much easier if the built-in functions supported vectors. Where the vector is of the right type of course.

• Much of the above can be done with recursive functions IF there was a vector concatenate operator or function, e.g. v3=concat(v1,v2)