Initial data commit

Task/Monty-Hall-problem/SparForte/monty-hall-problem.sparforte

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+#!/usr/local/bin/spar
+pragma annotate( summary, "monty" )
+       @( description, "Run random simulations of the Monty Hall game. Show the" )
+       @( description, "effects of a strategy of the contestant always keeping" )
+       @( description, "his first guess so it can be contrasted with the" )
+       @( description, "strategy of the contestant always switching his guess." )
+       @( description, "Simulate at least a thousand games using three doors" )
+       @( description, "for each strategy and show the results in such a way as" )
+       @( description, "to make it easy to compare the effects of each strategy." )
+       @( see_also, "http://rosettacode.org/wiki/Monty_Hall_problem" )
+       @( author, "Ken O. Burtch" );
+pragma license( unrestricted );
+
+pragma restriction( no_external_commands );
+
+procedure monty is
+  num_iterations : constant positive := 100_000;
+  type action_type is (stay, switch);
+  type prize_type is (goat, pig, car);
+  doors : array(1..3) of prize_type;
+  type door_index is new positive;
+
+  -- place the prizes behind random doors
+
+  procedure set_prizes is
+  begin
+    doors( 1 ) := goat;
+    doors( 2 ) := pig;
+    doors( 3 ) := car;
+    arrays.shuffle( doors );
+  end set_prizes;
+
+  -- determine if the prize was chosen based on strategy
+
+  function play( action : action_type ) return prize_type is
+    chosen : door_index := door_index( numerics.rnd(3) );
+    monty : door_index;
+  begin
+    set_prizes;
+    for i in arrays.first(doors)..arrays.last(doors) loop
+       if i /= chosen and doors(i) /= car then
+          monty := i;
+       end if;
+    end loop;
+    if action = switch then
+       for i in arrays.first(doors)..arrays.last(doors) loop
+           if i /= monty and i /= chosen then
+              chosen := i;
+              exit;
+           end if;
+       end loop;
+    end if;
+    return doors( chosen );
+  end play;
+
+  winners : natural; -- times won
+  pct     : float;   -- percentage won
+
+begin
+  winners := 0;
+  for i in 1..num_iterations loop
+      if play( stay ) = car then
+         winners := @+1;
+      end if;
+  end loop;
+  pct := float( winners * 100 ) / float( num_iterations );
+  put( "Stay: count" ) @ ( winners ) @ ( " = " ) @ ( pct ) @ ( "%" );
+  new_line;
+  winners := 0;
+  for i in 1..num_iterations loop
+      if play( switch ) = car then
+         winners := @+1;
+      end if;
+  end loop;
+  pct := float( winners * 100 ) / float( num_iterations );
+  put( "Switch: count" ) @ ( winners ) @ ( " = " ) @ ( pct ) @ ( "%" );
+  new_line;
+end monty;