pascal.erl

-module(pascal).
-export([triangle/1]).

triangle(Rows) ->
  triangle([[0,1,0]],1,Rows).

triangle(List, Count, Rows) when Count >= Rows -> lists:reverse(List);

triangle(List, Count, Rows) ->
  [Previous | _] = List,
  triangle([add_row(Previous) | List], Count+1, Rows).

add_row(Initial) ->
  add_row(Initial, 0, []). % last initialize to zero

add_row([], 0, Final) ->
  [0 | Final];

add_row([H | T], Last, New) ->
  add_row(T, H, [Last + H | New]).





%%       1
%%     1   1
%%   1   2   1
%% 1   3   3   1

%% Endpoint: no element left in the old list
%% Rule: new element = current + next

%% Trace:
%% H  T    Last  New      T      H   [Last + H | New]
%% 0 [1,0] 0     []    => [1,0], 0,  [0]
%% 1 [0]   0     [0]   => [0],   1,  [1,0]
%% 0 []    1     [1,0] => [],    0,  [1,1,0]