I have been using the Alloy API which can be written in Java. My goal is to compile Alloy model, display it visually, and narrow down the search for instances.
At this time, I need to command the source of the Alloy language, which may execute correctly or throw a NullPointerException, depending on the source. I have checked the contents of the API class in the eclipse debugger, but I cannot understand it properly.
The issue is: The debugger shows that TranslateAlloyToKodkod.execute_command occurs java.lang.NullPointerException.
According to the Alloy API documentation,
TranslateAlloyToKodkod.execute_commandreturns null if the user chose "save to FILE" as the SAT solver, and nonnull if the solver finishes the entire solving and is either satisfiable or unsatisfiable.
But I never changed execute options that "save to FILE" as the SAT solver. For your information, the solver, Alloy analyzer finishes the entire solving of following two sources.
Would you let me know how to fix the problem?
Here is the Java code I created, with some additions from the API example:
import java.io.File;
import edu.mit.csail.sdg.alloy4.A4Reporter;
import edu.mit.csail.sdg.alloy4.Err;
import edu.mit.csail.sdg.alloy4.ErrorWarning;
import edu.mit.csail.sdg.alloy4compiler.ast.Command;
import edu.mit.csail.sdg.alloy4compiler.ast.Module;
import edu.mit.csail.sdg.alloy4compiler.parser.CompUtil;
import edu.mit.csail.sdg.alloy4compiler.translator.A4Options;
import edu.mit.csail.sdg.alloy4compiler.translator.A4Solution;
import edu.mit.csail.sdg.alloy4compiler.translator.TranslateAlloyToKodkod;
import edu.mit.csail.sdg.alloy4viz.VizGUI;
public final class exportXML {
private static String outputfilepath;
public static void main(String[] args) throws Err {
VizGUI viz = null;
A4Reporter rep = new A4Reporter() {
@Override public void warning(ErrorWarning msg) {
System.out.print("Relevance Warning:\n"+(msg.toString().trim())+"\n\n");
System.out.flush();
}
};
String args_filename = args[0];
String[] path_split = args_filename.split("/");
int pos_fname = path_split.length -1;
String[] filename_split = path_split[pos_fname].split("\\.");
for ( int i=0; i<filename_split.length; i++ ) {
System.out.println(filename_split[i]);
}
String dir = "";
for ( int i = 0; i < path_split.length - 1; i++ ) {
dir = dir.concat(path_split[i]) + "/";
}
String out_fname = "Instance_of_" + filename_split[0];
outputfilepath = dir + out_fname;
File outdir = new File(outputfilepath);
outdir.mkdir();
for(String filename:args) {
System.out.println("=========== parse + typechecking: "+filename+" =============");
Module world = CompUtil.parseEverything_fromFile(rep, null, filename);
A4Options options = new A4Options();
options.solver = A4Options.SatSolver.SAT4J;
for (Command command: world.getAllCommands()) {
System.out.println("=========== command : "+command+" ============");
A4Solution ans = TranslateAlloyToKodkod.execute_command(rep, world.getAllReachableSigs(), command, options);
System.out.println(ans);
if (ans.satisfiable()) {
int cnt = 1;
A4Solution tmp = ans.next();
while ( tmp.satisfiable() ) {
tmp = tmp.next();
cnt++;
}
System.out.println("=========== "+cnt+" satisfiable solution found ============");
tmp = ans;
String[] outXml = new String[cnt];
for ( int i = 0; i < cnt; i++ ) {
outXml[i] = outputfilepath + "/" + out_fname + String.valueOf(i+1) + ".xml";
tmp.writeXML(outXml[i]);
tmp = tmp.next();
}
}
}
}
}
}
This is the sample of Alloy sources that will be successfully executed:
module adressBook
open ordering [Book]
abstract sig Target {}
sig Addr extends Target {}
abstract sig Name extends Target {}
sig Alias, Group extends Name {}
sig Book {
names: set Name,
addr: names -> some Target
}
{
no n: Name | n in n.^(addr)
all a: Alias | lone a.addr
}
pred add (b, b': Book, n: Name, t: Target) {
t in Addr or some lookup [b, t]
b'.addr = b.addr + n -> t
}
pred del (b, b': Book, n: Name, t: Target) {
no b.addr.n or some n.(b.addr) - t
b'.addr = b.addr - n -> t
}
fun lookup (b: Book, n: Name): set Addr {
n.^(b.addr) & Addr
}
pred init (b: Book) {no b.addr}
fact traces {
init [first]
all b: Book - last | let b' = next [b] |
some n: Name, t: Target | add [b, b', n, t] or del [b, b', n, t]
}
pred show {}
run show for 10
assert lookupYields {
all b: Book, n: b.names | some lookup [b, n]
}
check lookupYields for 3 but 4 Book
check lookupYields for 6
This is the Alloy source that will fail to execute (it will throw a null pointer):
sig Element {}
one sig Group {
elements: set Element,
unit: one elements,
mult: elements -> elements -> one elements,
inv: elements -> one elements
}
fact NoRedundantElements {
all e: Element | e in Group.elements
}
fact UnitLaw1 {
all a: Group.elements | Group.mult [a] [Group.unit] = a
}
fact UnitLaw2 {
all a: Group.elements |
Group.mult [Group.unit] [a] = a
}
fact AssociativeLaw {
all a: Group.elements | all b: Group.elements | all c:Group.elements |
Group.mult [Group.mult [a] [b]] [c] = Group.mult [a] [Group.mult [b] [c]]
}
fact InvLaw1{
all a: Group.elements | Group.mult [Group.inv[a]] [a] = Group.unit
}
assert InvLaw2 {
all a: Group.elements | Group.mult [a] [Group.inv[a]] = Group.unit
}
check InvLaw2
assert Commutativity {
all a: Group.elements | all b: Group.elements | Group.mult [a] [b] = Group.mult [b] [a]
}
check Commutativity for 6
pred subgroup (g: set Element, h: set Element) {
(all a: g | a in h) and
(Group.unit in g) and
(all a, b: g | Group.mult [a] [b] in g) and
(all a: g | Group.inv[a] in g)
}
pred regularSubgroup(n: set Element, g: set Element) {
subgroup [n, g] and
(all n0: n, g0: g | Group.mult [Group.mult [g0] [n0]] [Group.inv[g0]] in n)
}
pred main(n1: set Element, n2: set Element) {
let g = Group.elements |
regularSubgroup [n1, g] and
(some g0: g | (not g0 in n1)) and
regularSubgroup [n2, n1] and
(some n10: n1 | (not n10 in n2)) and
(not regularSubgroup [n2, g])
}
run main for 8
I think this should be reported as an issue on the https://github.com/alloytools/org.alloytools.alloy site? Preferably with a PR that fixes it.