go =>
  S = "Picat is fun",
  N = 3,
  M = 4,
  C = 'i', % must be a char
  SS = "is",
  test(S,N,M,C,SS).

test(S,N,M,C,SS) =>
  println($test(S,N,M,C,SS)),

  % - starting from n characters in and of m length;
  println(1=slice(S,N,N+M)),
  println(1=S[N..N+M]),

  % - starting from n characters in, up to the end of the string;
  println(2=S.slice(N)),

  % - whole string minus last character;
  println(3=but_last(S)),
  println(3=S[1..S.len-1]),

  % - starting from a known character within the string and of m length;
  println(4=substring4(S,C)),

  % - starting from a known substring within the string and of m length.
  println(5=substring5(S,SS,M)),
  nl.

but_last(S) = slice(S,1,S.length-1).

substring4(S,C) = slice(S,S.find_first_of(C)).

% find is non-deterministic, hence the once/1
substring5(S,SS,M) = slice(S,Start,Start+M) =>
  once(find(S,SS,Start,_End)).