Forlan Manual

The Debug Module

Synopsis

signature DEBUG
structure Debug :> DEBUG

This module contains a function for debugging Forlan code.

Interface

val debug : ('a -> PP.pp) -> PP.pp * 'a -> 'a

Description

debug h
returns the function that, when called with (msgPP, x), prints on the standard output PP.toString msgPP, followed by a colon, followed by PP.toString(h x), followed by a newline, followed by "(press RETURN to continue or interrupt character to interrupt) "; it then waits for user input; if the user responds by typing RETURN, then the function will return x.
Example:

We can instrument the factorial function 

  fun fact n =
        if n = 0
        then 1
        else n * fact(n - 1);
for debugging as follows: 
  val debugInt = Debug.debug(PP.fromString o Int.toString);

  fun fact n =
        debugInt
        (PP.fromString
         ("returning from fact " ^ Int.toString n ^ " with result"),
         if debugInt(PP.fromString "entering fact with argument", n) = 0
         then 1
         else n * fact(n - 1));


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