Use Prolog.Feature to control reflection, IO

The Prolog.Feature settings now control what features are available
to the running interpreter. Currently there are:

 * JAVA_REFLECTION: Use the java_* predicates.
 * IO:              Access to the local filesystem and console.

18 files changed, 115 insertions, 47 deletions

diff --git a/src/builtin/PRED_close_2.java b/src/builtin/PRED_close_2.java
index 4d7237c..e028100 100644
--- a/src/builtin/PRED_close_2.java
+++ b/src/builtin/PRED_close_2.java
@@ -20,6 +20,7 @@ public class PRED_close_2 extends Predicate.P2 {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.IO, this, arg1);
         engine.setB0();
         Term a1, a2;
         a1 = arg1;
diff --git a/src/builtin/PRED_current_input_1.java b/src/builtin/PRED_current_input_1.java
index fc1f2a2..fc4a0b9 100644
--- a/src/builtin/PRED_current_input_1.java
+++ b/src/builtin/PRED_current_input_1.java
@@ -13,6 +13,7 @@ public class PRED_current_input_1 extends Predicate.P1 {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.IO, this, arg1);
         engine.setB0();
 	Term a1;
 	a1 = arg1;
diff --git a/src/builtin/PRED_current_output_1.java b/src/builtin/PRED_current_output_1.java
index 0741e4a..4638118 100644
--- a/src/builtin/PRED_current_output_1.java
+++ b/src/builtin/PRED_current_output_1.java
@@ -13,6 +13,7 @@ public class PRED_current_output_1 extends Predicate.P1 {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.IO, this, arg1);
         engine.setB0();
 	Term a1;
 	a1 = arg1;
diff --git a/src/builtin/PRED_exists_directory_1.java b/src/builtin/PRED_exists_directory_1.java
index c63fff2..16ecaee 100644
--- a/src/builtin/PRED_exists_directory_1.java
+++ b/src/builtin/PRED_exists_directory_1.java
@@ -20,6 +20,7 @@ public class PRED_exists_directory_1 extends Predicate.P1 {
 
   @Override
   public Operation exec(Prolog engine) throws PrologException {
+    engine.requireFeature(Prolog.Feature.IO, this, arg1);
     engine.setB0();
 
     Term a1 = arg1.dereference();
diff --git a/src/builtin/PRED_exists_file_1.java b/src/builtin/PRED_exists_file_1.java
index 4703824..1aaebc0 100644
--- a/src/builtin/PRED_exists_file_1.java
+++ b/src/builtin/PRED_exists_file_1.java
@@ -20,6 +20,7 @@ public class PRED_exists_file_1 extends Predicate.P1 {
 
   @Override
   public Operation exec(Prolog engine) throws PrologException {
+    engine.requireFeature(Prolog.Feature.IO, this, arg1);
     engine.setB0();
 
     Term a1 = arg1.dereference();
diff --git a/src/builtin/PRED_file_directory_name_2.java b/src/builtin/PRED_file_directory_name_2.java
index 49aad15..739c223 100644
--- a/src/builtin/PRED_file_directory_name_2.java
+++ b/src/builtin/PRED_file_directory_name_2.java
@@ -22,6 +22,7 @@ public class PRED_file_directory_name_2 extends Predicate.P2 {
 
   @Override
   public Operation exec(Prolog engine) throws PrologException {
+    engine.requireFeature(Prolog.Feature.IO, this, arg1);
     engine.setB0();
 
     Term a1 = arg1.dereference();
diff --git a/src/builtin/PRED_java_constructor0_2.java b/src/builtin/PRED_java_constructor0_2.java
index c6da4c8..e76e22c 100644
--- a/src/builtin/PRED_java_constructor0_2.java
+++ b/src/builtin/PRED_java_constructor0_2.java
@@ -17,9 +17,8 @@ public class PRED_java_constructor0_2 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_declared_constructor0_2.java b/src/builtin/PRED_java_declared_constructor0_2.java
index 7e1a596..64e8836 100644
--- a/src/builtin/PRED_java_declared_constructor0_2.java
+++ b/src/builtin/PRED_java_declared_constructor0_2.java
@@ -17,9 +17,8 @@ public class PRED_java_declared_constructor0_2 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_declared_method0_3.java b/src/builtin/PRED_java_declared_method0_3.java
index e1fa3e6..37877df 100644
--- a/src/builtin/PRED_java_declared_method0_3.java
+++ b/src/builtin/PRED_java_declared_method0_3.java
@@ -18,9 +18,8 @@ public class PRED_java_declared_method0_3 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2, a3;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_get_declared_field0_3.java b/src/builtin/PRED_java_get_declared_field0_3.java
index 0a76452..0e8265f 100644
--- a/src/builtin/PRED_java_get_declared_field0_3.java
+++ b/src/builtin/PRED_java_get_declared_field0_3.java
@@ -18,9 +18,8 @@ public class PRED_java_get_declared_field0_3 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2, a3;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_get_field0_3.java b/src/builtin/PRED_java_get_field0_3.java
index 3c8a7b0..ff4d084 100644
--- a/src/builtin/PRED_java_get_field0_3.java
+++ b/src/builtin/PRED_java_get_field0_3.java
@@ -18,9 +18,8 @@ public class PRED_java_get_field0_3 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2, a3;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_method0_3.java b/src/builtin/PRED_java_method0_3.java
index b9a83c7..5fc6fad 100644
--- a/src/builtin/PRED_java_method0_3.java
+++ b/src/builtin/PRED_java_method0_3.java
@@ -18,9 +18,8 @@ public class PRED_java_method0_3 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2, a3;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_set_declared_field0_3.java b/src/builtin/PRED_java_set_declared_field0_3.java
index 1fcc6c0..451851e 100644
--- a/src/builtin/PRED_java_set_declared_field0_3.java
+++ b/src/builtin/PRED_java_set_declared_field0_3.java
@@ -18,9 +18,8 @@ public class PRED_java_set_declared_field0_3 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2, a3;
 	a1 = arg1;
diff --git a/src/builtin/PRED_java_set_field0_3.java b/src/builtin/PRED_java_set_field0_3.java
index 1aca99f..133d8ff 100644
--- a/src/builtin/PRED_java_set_field0_3.java
+++ b/src/builtin/PRED_java_set_field0_3.java
@@ -18,9 +18,8 @@ public class PRED_java_set_field0_3 extends JavaPredicate {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.JAVA_REFLECTION, this, arg1);
         engine.setB0();
-        if (!engine.control.getEnableReflection())
-          throw new PermissionException(this, "reflection", "call", arg1, "disabled");
 
 	Term a1, a2, a3;
 	a1 = arg1;
diff --git a/src/builtin/PRED_make_directory_1.java b/src/builtin/PRED_make_directory_1.java
index fa9a463..fc4b678 100644
--- a/src/builtin/PRED_make_directory_1.java
+++ b/src/builtin/PRED_make_directory_1.java
@@ -21,6 +21,7 @@ public class PRED_make_directory_1 extends Predicate.P1 {
 
   @Override
   public Operation exec(Prolog engine) throws PrologException {
+    engine.requireFeature(Prolog.Feature.IO, this, arg1);
     engine.setB0();
 
     Term a1 = arg1.dereference();
diff --git a/src/builtin/PRED_open_4.java b/src/builtin/PRED_open_4.java
index 24e482c..438df3c 100644
--- a/src/builtin/PRED_open_4.java
+++ b/src/builtin/PRED_open_4.java
@@ -29,6 +29,7 @@ public class PRED_open_4 extends Predicate.P4 {
     }
 
     public Operation exec(Prolog engine) {
+        engine.requireFeature(Prolog.Feature.IO, this, arg1);
         engine.setB0();
 	File file;
 	Term alias = null;
diff --git a/src/lang/Prolog.java b/src/lang/Prolog.java
index b74bfd8..1510732 100644
--- a/src/lang/Prolog.java
+++ b/src/lang/Prolog.java
@@ -1,6 +1,15 @@
 package com.googlecode.prolog_cafe.lang;
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.PushbackReader;
+import java.io.Reader;
+import java.io.Writer;
+import java.util.EnumSet;
 import java.util.HashMap;
-import java.io.*;
 /**
  * Prolog engine.
  *
@@ -111,6 +120,15 @@ public final class Prolog {
     static final SymbolTerm SYM_USEROUTPUT = SymbolTerm.makeSymbol("user_output");
     static final SymbolTerm SYM_USERERROR  = SymbolTerm.makeSymbol("user_error");
 
+    public static enum Feature {
+      /** Enable the {@code java_*} predicates, supporting reflection in Prolog. */
+      JAVA_REFLECTION,
+
+      /** Access to the local filesystem and console. */
+      IO;
+    }
+    protected final EnumSet<Feature> features = EnumSet.allOf(Feature.class);
+
     /** Constructs new Prolog engine. */
     public Prolog(PrologControl c) { 
 	control    = c;
@@ -120,7 +138,7 @@ public final class Prolog {
 	hashManager = new HashtableOfTerm();
     }
 
-    /** 
+    /**
      * Initializes some local instances only once.
      * This <code>initOnce</code> method is invoked in the constructor
      * and initializes the following instances:
@@ -132,30 +150,59 @@ public final class Prolog {
      *   <li><code>streamManager</code>
      * </ul>
      */
-    protected void initOnce() {
-	aregs = new Term[Math.max(0, maxArity - 8)];
-	if (pcl == null)
-	  pcl = new PrologClassLoader();
-	if (internalDB == null)
-	  internalDB = new InternalDatabase();
-
-	userInput   = new PushbackReader(new BufferedReader(new InputStreamReader(System.in)), PUSHBACK_SIZE);
-	userOutput  = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)), true);
-	userError   = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.err)), true);
-
-	copyHash      = new HashMap<VariableTerm,VariableTerm>();
-	streamManager = new HashtableOfTerm();
-
-	streamManager.put(SYM_USERINPUT, new JavaObjectTerm(userInput));
-	streamManager.put(new JavaObjectTerm(userInput), 
-			  makeStreamProperty(SYM_READ, SYM_INPUT, SYM_USERINPUT, SYM_TEXT));
-	streamManager.put(SYM_USEROUTPUT, new JavaObjectTerm(userOutput));
-	streamManager.put(new JavaObjectTerm(userOutput),
-			  makeStreamProperty(SYM_APPEND, SYM_OUTPUT, SYM_USEROUTPUT, SYM_TEXT));
-	streamManager.put(SYM_USERERROR, new JavaObjectTerm(userError));
-	streamManager.put(new JavaObjectTerm(userError),
-			  makeStreamProperty(SYM_APPEND, SYM_OUTPUT, SYM_USERERROR, SYM_TEXT));
+  protected void initOnce() {
+    aregs = new Term[Math.max(0, maxArity - 8)];
+    if (pcl == null) pcl = new PrologClassLoader();
+    if (internalDB == null) internalDB = new InternalDatabase();
+
+    copyHash = new HashMap<VariableTerm, VariableTerm>();
+    streamManager = new HashtableOfTerm();
+
+    if (features.contains(Feature.IO)) {
+      userInput = new PushbackReader(new BufferedReader(new InputStreamReader(System.in)), PUSHBACK_SIZE);
+      userOutput = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)), true);
+      userError = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.err)), true);
+
+      streamManager.put(SYM_USERINPUT, new JavaObjectTerm(userInput));
+      streamManager.put(new JavaObjectTerm(userInput),
+        makeStreamProperty(SYM_READ, SYM_INPUT, SYM_USERINPUT, SYM_TEXT));
+
+      streamManager.put(SYM_USEROUTPUT, new JavaObjectTerm(userOutput));
+      streamManager.put(new JavaObjectTerm(userOutput),
+        makeStreamProperty(SYM_APPEND, SYM_OUTPUT, SYM_USEROUTPUT, SYM_TEXT));
+
+      streamManager.put(SYM_USERERROR, new JavaObjectTerm(userError));
+      streamManager.put(new JavaObjectTerm(userError),
+        makeStreamProperty(SYM_APPEND, SYM_OUTPUT, SYM_USERERROR, SYM_TEXT));
+    } else {
+      userInput = new PushbackReader(new Reader() {
+        @Override
+        public int read(char[] cbuf, int off, int len) throws IOException {
+          return -1;
+        }
+
+        @Override
+        public void close() throws IOException {
+        }
+      });
+
+      userOutput = new PrintWriter(new Writer() {
+        @Override
+        public void write(char[] cbuf, int off, int len) throws IOException {
+          throw new IOException("Prolog.Feature.IO disabled");
+        }
+
+        @Override
+        public void flush() throws IOException {
+        }
+
+        @Override
+        public void close() throws IOException {
+        }
+      });
+      userError = userOutput;
     }
+  }
 
     /** Initializes this Prolog engine. */
     public void init() { 
@@ -194,6 +241,13 @@ public final class Prolog {
 	currentOutput = userOutput;
     }
 
+    /** Ensure a feature is enabled, throwing if not. */
+    public void requireFeature(Prolog.Feature f, Operation goal, Term arg) {
+      if (!features.contains(f)) {
+        throw new PermissionException(goal, "use", f.toString().toLowerCase(), arg, "disabled");
+      }
+    }
+
     /** Sets B0 to the top of the choice point stack.. */
     public void setB0()    { B0 = stack.top(); }
 
diff --git a/src/lang/PrologControl.java b/src/lang/PrologControl.java
index 91b1834..cb4d5b0 100644
--- a/src/lang/PrologControl.java
+++ b/src/lang/PrologControl.java
@@ -1,4 +1,7 @@
 package com.googlecode.prolog_cafe.lang;
+
+import java.util.Set;
+
 /**
  * Tracks current evaluation goal and results.
  * <p>
@@ -18,18 +21,29 @@ public abstract class PrologControl {
     /** Holds a Prolog goal to be executed. */
     protected Operation code;
 
-    /** Should Java reflection be permitted. */
-    private boolean enableReflection;
-
     /** Constructs a new <code>PrologControl</code>. */
     public PrologControl() {
 	engine = new Prolog(this);
 	code = null;
-	enableReflection = true;
     }
 
-    public boolean getEnableReflection() { return enableReflection; }
-    public void setEnableReflection(boolean on) { enableReflection = on; }
+    public boolean isEnabled(Prolog.Feature f) {
+      return engine.features.contains(f);
+    }
+
+    public void setEnabled(Prolog.Feature f, boolean on) {
+      if (on)
+        engine.features.add(f);
+      else
+        engine.features.remove(f);
+    }
+
+    public void setEnabled(Set<Prolog.Feature> f, boolean on) {
+      if (on)
+        engine.features.addAll(f);
+      else
+        engine.features.removeAll(f);
+    }
 
     public int getMaxDatabaseSize() {
       if (engine.internalDB != null)