7 files changed, 72 insertions, 83 deletions
diff --git a/src/main/java/au/id/zancanaro/javacheck/statem/Command.java b/src/main/java/au/id/zancanaro/javacheck/state/Command.java
index a741f0a..afa3957 100644
--- a/src/main/java/au/id/zancanaro/javacheck/statem/Command.java
+++ b/src/main/java/au/id/zancanaro/javacheck/state/Command.java
@@ -1,4 +1,4 @@
-package au.id.zancanaro.javacheck.statem;
+package au.id.zancanaro.javacheck.state;
 
 import au.id.zancanaro.javacheck.Generator;
 
diff --git a/src/main/java/au/id/zancanaro/javacheck/statem/CommandList.java b/src/main/java/au/id/zancanaro/javacheck/state/CommandList.java
index 9e8948a..0426fd3 100644
--- a/src/main/java/au/id/zancanaro/javacheck/statem/CommandList.java
+++ b/src/main/java/au/id/zancanaro/javacheck/state/CommandList.java
@@ -1,9 +1,6 @@
-package au.id.zancanaro.javacheck.statem;
+package au.id.zancanaro.javacheck.state;
 
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 public class CommandList<State> {
     private final List<GeneratedCommand<State, ?, ?>> commands;
@@ -35,11 +32,14 @@ public class CommandList<State> {
             if (!command.preCondition(state, args)) {
                 return CommandResult.fail(state, new Error("Precondition failed"));
             }
-            Result result = command.runCommand(args);
+            Result result = CommandValue.withValues(values, () ->
+                    command.runCommand(args));
             values.put(id, result);
-            State oldState = state;
-            state = command.nextState(state, args, new CommandValue.ConcreteValue<>(id, values));
-            if (!command.postCondition(oldState, state, args, result)) {
+            final State oldState = state;
+            final State newState = CommandValue.withValues(values, () ->
+                    command.nextState(oldState, args, new CommandValue<>(id)));
+            state = newState;
+            if (!CommandValue.withValues(values, () -> command.postCondition(oldState, newState, args, result))) {
                 return CommandResult.fail(state, new Error("Postcondition failed"));
             }
             return CommandResult.success(state);
@@ -58,7 +58,7 @@ public class CommandList<State> {
             if (!command.preCondition(state, args)) {
                 return CommandResult.fail(state, new Error("Precondition failed"));
             }
-            state = command.nextState(state, args, new CommandValue.AbstractValue<>(id));
+            state = command.nextState(state, args, new CommandValue<>(id));
             return CommandResult.success(state);
         } catch (Throwable ex) {
             return CommandResult.fail(state, ex);
@@ -78,8 +78,14 @@ public class CommandList<State> {
 
     @Override
     public String toString() {
-        return "CommandList{" +
-                "commands=" + commands +
-                '}';
+        StringBuilder builder = new StringBuilder();
+        Iterator<GeneratedCommand<State, ?, ?>> iterator = commands.iterator();
+        while (iterator.hasNext()) {
+            builder.append(iterator.next());
+            if (iterator.hasNext()) {
+                builder.append(", ");
+            }
+        }
+        return builder.toString();
     }
 }
diff --git a/src/main/java/au/id/zancanaro/javacheck/statem/CommandListGenerator.java b/src/main/java/au/id/zancanaro/javacheck/state/CommandListGenerator.java
index a0df66f..4c2c47f 100644
--- a/src/main/java/au/id/zancanaro/javacheck/statem/CommandListGenerator.java
+++ b/src/main/java/au/id/zancanaro/javacheck/state/CommandListGenerator.java
@@ -1,4 +1,4 @@
-package au.id.zancanaro.javacheck.statem;
+package au.id.zancanaro.javacheck.state;
 
 import au.id.zancanaro.javacheck.Generator;
 import au.id.zancanaro.javacheck.ShrinkTree;
@@ -29,7 +29,7 @@ public class CommandListGenerator<State> implements Generator<CommandList<State>
     }
 
     public <Args, Result> State nextState(int id, GeneratedCommand<State, Args, Result> generatedCommand, State state) {
-        return generatedCommand.getCommand().nextState(state, generatedCommand.getArgs(), new CommandValue.AbstractValue<>(id));
+        return generatedCommand.getCommand().nextState(state, generatedCommand.getArgs(), new CommandValue<>(id));
     }
 
     @Override
diff --git a/src/main/java/au/id/zancanaro/javacheck/statem/CommandResult.java b/src/main/java/au/id/zancanaro/javacheck/state/CommandResult.java
index dc5b085..12f650d 100644
--- a/src/main/java/au/id/zancanaro/javacheck/statem/CommandResult.java
+++ b/src/main/java/au/id/zancanaro/javacheck/state/CommandResult.java
@@ -1,4 +1,4 @@
-package au.id.zancanaro.javacheck.statem;
+package au.id.zancanaro.javacheck.state;
 
 public class CommandResult<State> {
     private final State state;
diff --git a/src/main/java/au/id/zancanaro/javacheck/state/CommandValue.java b/src/main/java/au/id/zancanaro/javacheck/state/CommandValue.java
new file mode 100644
index 0000000..8d3f272
--- /dev/null
+++ b/src/main/java/au/id/zancanaro/javacheck/state/CommandValue.java
@@ -0,0 +1,47 @@
+package au.id.zancanaro.javacheck.state;
+
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.function.Supplier;
+
+public class CommandValue<T> {
+    private static Map<Integer, Object> values = null;
+
+    public static <T> T withValues(Map<Integer, Object> newValues, Supplier<T> action) {
+        Map<Integer,Object> oldValues = values;
+        try {
+            values = newValues;
+            return action.get();
+        } finally {
+            values = oldValues;
+        }
+    }
+
+    private final int id;
+
+    public CommandValue(int id) {
+        this.id = id;
+    }
+
+    public boolean isAbstract() {
+        return values == null;
+    }
+
+    @SuppressWarnings("unchecked")
+    public T get() {
+        if (values.containsKey(getId())) {
+            return (T) values.get(getId());
+        } else {
+            throw new NoSuchElementException("Concrete values cannot be supplied prior to being calculated");
+        }
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    @Override
+    public String toString() {
+        return "#{" + id + "}";
+    }
+}
diff --git a/src/main/java/au/id/zancanaro/javacheck/statem/GeneratedCommand.java b/src/main/java/au/id/zancanaro/javacheck/state/GeneratedCommand.java
index 5e576b4..90d9a47 100644
--- a/src/main/java/au/id/zancanaro/javacheck/statem/GeneratedCommand.java
+++ b/src/main/java/au/id/zancanaro/javacheck/state/GeneratedCommand.java
@@ -1,4 +1,4 @@
-package au.id.zancanaro.javacheck.statem;
+package au.id.zancanaro.javacheck.state;
 
 public class GeneratedCommand<State, Args, Result> {
     private final int id;
@@ -47,10 +47,6 @@ public class GeneratedCommand<State, Args, Result> {
 
     @Override
     public String toString() {
-        return "GeneratedCommand{" +
-                "id=" + id +
-                ", command=" + command +
-                ", args=" + args +
-                '}';
+        return "#{" + id + "} = " + command + " <- " + args;
     }
 }
diff --git a/src/main/java/au/id/zancanaro/javacheck/statem/CommandValue.java b/src/main/java/au/id/zancanaro/javacheck/statem/CommandValue.java
deleted file mode 100644
index 0a1fb61..0000000
--- a/src/main/java/au/id/zancanaro/javacheck/statem/CommandValue.java
+++ /dev/null
@@ -1,60 +0,0 @@
-package au.id.zancanaro.javacheck.statem;
-
-import java.util.Map;
-import java.util.NoSuchElementException;
-
-public abstract class CommandValue<T> {
-    private final int id;
-
-    public CommandValue(int id) {
-        this.id = id;
-    }
-
-    public abstract boolean isAbstract();
-
-    public abstract T get();
-
-    public int getId() {
-        return id;
-    }
-
-    static class AbstractValue<T> extends CommandValue<T> {
-        public AbstractValue(int id) {
-            super(id);
-        }
-
-        @Override
-        public boolean isAbstract() {
-            return true;
-        }
-
-        @Override
-        public T get() {
-            throw new NoSuchElementException("Abstract values cannot be supplied");
-        }
-    }
-
-    static class ConcreteValue<T> extends CommandValue<T> {
-        private final Map<Integer, Object> values;
-
-        public ConcreteValue(int id, Map<Integer, Object> values) {
-            super(id);
-            this.values = values;
-        }
-
-        @Override
-        public boolean isAbstract() {
-            return true;
-        }
-
-        @Override
-        @SuppressWarnings("unchecked")
-        public T get() {
-            if (values.containsKey(getId())) {
-                return (T) values.get(getId());
-            } else {
-                throw new NoSuchElementException("Concrete values cannot be supplied prior to being calculated");
-            }
-        }
-    }
-}