True

From the SETL Wiki

true is the name of the predefined boolean constant that represents logical truth in SETL (like most high-level languages.)

Operations involving true include:

• Use it as the condition in an if statement:

  if true then
    print('You should see this');
  else
    print('You should not see this');
  end;
  

  
  

• Use it as the condition in an while statement:

  (while true)
    print('You should see this repeated infinitely');
  end while;
  
  (until true)
    print('You should not see this');
  end until;
  

  
  

• Convert it to a string:

  str true
  

  Result: '#t'

• Parse it from a string:

  unstr '#T'
  

  Result:true

• Query its type:

  print(type true, is_boolean true, is_integer true, denotype '#t');
  

  Output:BOOLEAN #T #F BOOLEAN

• Insert it into a set or map:

  s := {true};
  true in s;
  false in s;
  
  not_map := {[true, false], [false, true]};
  not_map(true);
  not_map(false);
  

  Results:
  #T
#F

#F
#T