System T in Twelf
To run, start twelf-server and load system-t.elf.
$ twelf-server
Twelf 1.7.1 ...
%%% OK %%
loadFile system-t.elf
top
?- has-typ (lam nat [x] x) T.
Solving...
T = nat => nat.
You can evaluate things like this:
?- step (ap (lam nat [x] (s x)) (s s z)) E.
Solving...
E = s s s z.