% tail_call - Simulate effect of tail call
%
% tail_call :: (A{1:N}->B{1:M}), A{1:N} -> thunk(B{1:M}).
%
% thunk(B{1:M}) ::= 
%    exists C{1:L} . cell { C{1:L}->B{1:M}, cell { C{1:L} } }
%  | cell { {0}, cell { B{1:L} } }
%  | unit -> B{1:M}.
function ret=tail_call(fn,varargin), ret={fn,varargin}; end
