Compiler Construction 2015
Computer Laboratory 
University of Cambridge 
Timothy G. Griffin (tgg22@cam.ac.uk) 

Practical Exercises, Set 1. (For slang1_interpret.)

There are many possible extensions or modifications 
possible for the Slang.1 that be fun programming 
(nested comments, better verbose output, etc). 
However, I'll list only those exercises that I feel 
reinforce the main points of the lectures. 

They are listed from easiest to hardest. 


) In this simple language, do we really need the 
  return types of functions? Could we always infer them? 

) Add division to the arithmetic operations. How will 
  you handle division by zero? 

) We have blurred the distinction between the defining 
  language (OCaml) and the defined language (Slang.1) 
  in several ways.  For example, Slang.1 integers are 
  the ints supplied by OCaml on your machine. Now 
  suppose that Slang.1 only allows 16-bit integers, 
  where overflow or underflow should raise a 
  run-time error.  Can you modify the implementation 
  to match this? Are there additional build-in functions 
  that you might want to add to such a language? 
    
) Add mutual recursion to Slang1.  Such as 

    let g(x : int) : int = ... f(e) ... 
    and f(z :int) : int  = .... g(e') ... 
    in ... end 

   This requires careful treatment of environments! 

) Consider adding references to Slang.1. We could do 
  this in several ways, from simplest to most complex: 
  --- Allow references to be used only locally. 
  --- Allow refs to be passed to functions and 
      then updated by the called function. 
  --- Allow refs to be returned by functions

  Can interp_0.ml be extended to handle each of these?