Awesome

Higher-Level-Transformer

Implementation of the higher-level transformers as described in the paper "The Next 700 Program Transformers"

The implementation can be built and executed using stack.

Execution

The execution is a REPL, with the prompt "POT> " and the following commands:

POT> :help

:load <filename>        To load the given filename  
:prog                   To print the current program  
:term                   To print the current term  
:eval                   To evaluate the current program  
:trans <int>            To transform the current program using a level <int> transformer.  
:quit                   To quit  
:help                   To print this message  

The first thing to do is to load a program file:

POT> :load nrev

This will load the program nrev.pot (the.pot extension is assumed).

To see the contents of this program:

POT> :prog  
main = nrev xs;
append xs ys = case xs of
                  Nil -> ys
                | Cons(x,xs) -> Cons(x,append xs ys);
nrev xs = case xs of
             Nil -> []
           | Cons(x,xs) -> (append (nrev xs) [x])

To see the top-level term:

POT> :term  
nrev xs

To apply the level 1 program transformer to the current program:

POT> :trans 1 
main = f xs;
f xs = case xs of
          Nil -> []
        | Cons(x,xs) -> (case (f xs) of
                            Nil -> [x]
                          | Cons(x',xs) -> Cons(x',append xs [x]));
append xs ys = case xs of
                  Nil -> ys
                | Cons(x,xs) -> Cons(x,append xs ys)  

To apply the level 2 program transformer to the current program:

POT> :trans 2
main = case xs of
          Nil -> []
        | Cons(x,xs) -> (f xs x []);
f xs' x x'' = case xs' of
                 Nil -> Cons(x,x'')
               | Cons(x',xs) -> (f xs x' Cons(x,x''))

To evaluate the current program:

POT> :eval

This will prompt for values of the free variables:

xs = [1,2,3,4,5,6,7,8,9]
[9,8,7,6,5,4,3,2,1]
Reductions: 118
Allocations: 10  

To quit from the program:

POT> :quit