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.
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