cek machine

cek.pl

% https://github.com/pycket/pycket/blob/master/papers/icfp15-paper.pdf
% e ::= x | λ(x,e) | e $ e | i | e + e | add(x,x)
% k ::= [] | [arg(e,p)|k] | [fun(v,p)|k]
:- op(1100,yfx,$).
v(I):- integer(I).
v(λ(_X,_E)).
cek(X/P/K                 , V/P/K):- atom(X),member(X->V,P).
cek((E1$E2)/P/K           , E1/P/[arg(E2,P)|K]).
cek(V/P/[arg(E,P_)|K]     , E/P_/[fun(V,P)|K]):- v(V).
cek(V/_/[fun(λ(X,E),P_)|K], E/[X->V|P_]/K):- v(V).
cek((E1+E2)/P/K           , λ(x,λ(y,add(x,y)))/P/[arg(E1,P),arg(E2,P)|K]).
cek(add(X,Y)/P/K          , I/P/K):- member(X->I1,P),member(Y->I2,P),I is I1+I2.
eval(CEK,CEK2):- cek(CEK,CEK1),!,eval(CEK1,CEK2).
eval(CEK,CEK).
run(E,R):- eval(E/[]/[],R/_/_).
:- run(1+2,R),writeln(R),R=3.
:- run(1+2+3,R),writeln(R),R=6.
:- run(λ(x,λ(y,x+y))$10$2,R),writeln(R),R=12.
:- halt.