X-Git-Url: http://git.megacz.com/?p=sbp.git;a=blobdiff_plain;f=src%2Fedu%2Fberkeley%2Fsbp%2Fmisc%2FDemo.java;h=c567eddaadf5c34af41b77f8ab969b17b54294f8;hp=92726187d3b8f47c9d6c45a13c0373eb54534c0c;hb=bb4357ee026741cacecdfbfdcdd2d44699306536;hpb=a96edcbb9051f33f65256dcd5adcbae6925956eb

diff --git a/src/edu/berkeley/sbp/misc/Demo.java b/src/edu/berkeley/sbp/misc/Demo.java
index 9272618..c567edd 100644
--- a/src/edu/berkeley/sbp/misc/Demo.java
+++ b/src/edu/berkeley/sbp/misc/Demo.java
@@ -3,17 +3,749 @@ import edu.berkeley.sbp.util.*;
 import edu.berkeley.sbp.*;
 import edu.berkeley.sbp.chr.*;
 import java.util.*;
+import java.lang.annotation.*;
+import java.lang.reflect.*;
 import java.io.*;
 
 public class Demo {
+    
+    public static boolean harsh = false;
+
     public static void main(String[] s) throws Exception {
-        Tree<String> gram = new CharParser(MetaGrammar.make()).parse(new FileInputStream(s[0])).expand1();
-        MetaGrammar g = (MetaGrammar)new MetaGrammar().walk(gram);
-        Union meta = g.done();
-        //Tree<String> out = new CharParser(meta).parse(new FileInputStream(s[1])).expand1();
-        Forest<String> out = new CharParser(meta).parse(new FileInputStream(s[1]));
-        GraphViz gv = new GraphViz();
-        out.toGraphViz(gv);
-        gv.dump(new PrintWriter(new OutputStreamWriter(System.out)));
+
+        ReflectiveMeta m = new ReflectiveMeta();
+        Tree<String> res = new CharParser(MetaGrammar.make()).parse(new FileInputStream(s[0])).expand1();
+        MetaGrammar.Meta.MetaGrammarFile mgf = m.new MetaGrammarFile(res);
+        MetaGrammar.BuildContext bc = new MetaGrammar.BuildContext(mgf);
+        Union meta = mgf.get("s").build(bc);
+        System.err.println("parsing " + s[1]);
+        Tree t = new CharParser(meta).parse(new FileInputStream(s[1])).expand1();
+        System.out.println("tree:\n" + t.toPrettyString());
+
+        Reducer red = (Reducer)t.head();
+        MG.Grammar g = (MG.Grammar)red.reduce(t);
+        System.out.println(g);
+        
+        Context cx = new Context(g,m);
+        Element u = null;
+        for(MG.NonTerminal nt : g.nonterminals) {
+            Union el = (Union)cx.get(nt.name);
+            StringBuffer st = new StringBuffer();
+            el.toString(st);
+            System.err.println(st);
+            if (nt.name.equals("s")) u = el;
+        }
+        System.err.println();
+
+        System.err.println("== parsing with parsed grammar =================================================================================");
+        t = new CharParser((Union)u).parse(new FileInputStream(s[1])).expand1();
+        System.out.println(t.toPrettyString());
+
+        System.err.println("== parsing with parsed-parsed grammar ==========================================================================");
+        t = new CharParser(new Context(t, m).build()).parse(new FileInputStream(s[1])).expand1();
+        System.out.println(t.toPrettyString());
+    }
+
+    public static class ReflectiveMeta extends MetaGrammar.Meta {
+        private final Class _cl;
+        private final Class[] _inner;
+        public ReflectiveMeta() {
+            this(MG.class,
+                 new Class[] {
+                     MG.Grammar.class,
+                     MG.NonTerminal.class,
+                     MG.AnonUn.class,
+                     MG.Range.class,
+                     MG.El.class,
+                     MG.Seq.class,
+                     MG.NonTerminalReference.class,
+                     MG.StringLiteral.class,
+                     MG.Tree.class,
+                     MG.CharClass.class
+                 });
+        }
+        public ReflectiveMeta(Class c, Class[] inner) {
+            this._cl = c;
+            this._inner = inner;
+        }
+        private boolean match(Method m, String s) { return match(m.getAnnotation(tag.class), null, s); }
+        private boolean match(tag t, Class c, String s) {
+            if (t==null) return false;
+            if (t.value().equals(s)) return true;
+            if (c != null && t.equals("") && c.getSimpleName().equals(s)) return true;
+            return false;
+        }
+        private boolean match(nonterminal t, Class c, String s) {
+            if (t==null) return false;
+            if (t.value().equals(s)) return true;
+            if (c != null && t.equals("") && c.getSimpleName().equals(s)) return true;
+            return false;
+        }
+        private boolean match(Class c, String s, String nonTerminalName) {
+            if (match((tag)c.getAnnotation(tag.class), c, s)) return true;
+            if (match((nonterminal)c.getAnnotation(nonterminal.class), c, nonTerminalName)) return true;
+            return false;
+        }
+        public boolean match(Constructor con, String s, String nonTerminalName) {
+            Class c = con.getDeclaringClass();
+            if (match((tag)con.getAnnotation(tag.class), null, s)) return true;
+            if (match((nonterminal)con.getAnnotation(nonterminal.class), c, s)) return true;
+            return false;
+        }
+        public Object repeatTag() {
+            return new Reducer() {
+                    public String toString() { return "[**]"; }
+                    public Object reduce(Tree t) {
+                        Object[] ret = new Object[t.numChildren()];
+                        for(int i=0; i<t.numChildren(); i++) {
+                            Tree tc = t.child(i);
+                            if (tc.head() != null && tc.head() instanceof Reducer)
+                                ret[i] = ((Reducer)tc.head()).reduce(tc);
+                            else if (tc.numChildren() == 0)
+                                ret[i] = tc.head();
+                            else {
+                                System.err.println("FIXME: don't know what to do about " + tc);
+                                ret[i] = null;
+                            }
+                        }
+                        return ret;
+                    }
+                };
+        }
+        public Sequence tryResolveTag(String tag, String nonTerminalName, Element[] els, Object[] labels, boolean[] drops) {
+            Production p = new Production(tag, nonTerminalName, els, labels, drops);
+            for(Method m : _cl.getMethods())
+                if (new TargetMethod(m).isCompatible(p))
+                    return new TargetMethod(m).makeSequence(p);
+            for(Class c : _inner)
+                for(Constructor con : c.getConstructors())
+                    if (new TargetConstructor(con).isCompatible(p))
+                        return new TargetConstructor(con).makeSequence(p);
+            for(Class c : _inner)
+                if (new TargetClass(c).isCompatible(p))
+                    return new TargetClass(c).makeSequence(p);
+            return null;
+        }
+        public Sequence resolveTag(String tag, String nonTerminalName, Element[] els, Object[] labels, boolean[] drops) {
+            Sequence ret = tryResolveTag(tag, nonTerminalName, els, labels, drops);
+            if (ret != null) return ret;
+            String message = "could not find a Java method/class/ctor matching tag \""+tag+
+                "\", nonterminal \""+nonTerminalName+"\" with " + els.length + " arguments";
+            if (harsh) {
+                throw new RuntimeException(message);
+            } else {
+                System.err.println(message);
+                return Sequence.rewritingSequence(tag, els, labels, drops);
+            }
+        }
+    }
+
+    
+    /**
+     *  Constructors, classes, and methods with this attribute will
+     *  match every production of the nonterminal called "value()"
+     *  that is arg-compatible.  If value() is undefined, then the
+     *  class/constructor/method name is used.
+     */ 
+    @Retention(RetentionPolicy.RUNTIME) public static @interface nonterminal { String value() default ""; }
+
+    /**
+     *  Constructors, classes, and methods with this attribute will
+     *  match every tree tagged with "value()" that is arg-compatible.
+     *  If value() is undefined, then the class/constructor/method
+     *  name is used.
+     */ 
+    @Retention(RetentionPolicy.RUNTIME) public static @interface tag         { String value() default ""; }
+
+    /**
+     *  If any parameter to a method or field in a class has a named
+     *  arg-tag, that parameter/field matches the child of the tree
+     *  which either has that label or else is a reference to a
+     *  nonterminal with the corresponding name.
+     *  
+     *  The remaining non-named arg-tags match the remaining children
+     *  of the tree in sequential order.
+     *
+     *  If any arg-tagged parameters/fields remain, the match fails.
+     *  If there were no arg-tagged parameters-fields, it is as if all
+     *  of them were non-named and arg-tagged.
+     *
+     *  A method/constructor is arg-compatible if all of its arguments
+     *  are arg-compatible.
+     *
+     *  A class is arg-compatible if all of its fields are
+     *  arg-compatible, or if one of its constructors is arg-compatible.
+     *
+     */
+    @Retention(RetentionPolicy.RUNTIME) public static @interface arg         { String value() default ""; }
+
+    public static class Production {
+        public String tag;
+        public String nonTerminal;
+        public Object[] labels;
+        public boolean[] drops;
+        public Element[] elements;
+        public int count = 0;
+        public Production(String tag, String nonTerminal, Element[] elements, Object[] labels, boolean[] drops) {
+            this.tag = tag;
+            this.elements = elements;
+            this.nonTerminal = nonTerminal;
+            this.labels = labels;
+            this.drops = drops;
+            for(int i=0; i<drops.length; i++)
+                if (!drops[i])
+                    count++;
+        }
+    }
+
+    public static abstract class Target {
+        public abstract String getName();
+        public abstract tag getTag();
+        public abstract nonterminal getNonTerminal();
+        public abstract int[] buildSequence(Production p);
+        public boolean isCompatible(Production p) {
+            tag t = getTag();
+            if (t != null &&
+                (t.value().equals(p.tag) ||
+                 (t.value().equals("") && p.tag.equals(getName()))))
+                return buildSequence(p)!=null;
+
+            nonterminal n = getNonTerminal();
+            if (n != null &&
+                (n.value().equals(p.nonTerminal) ||
+                 (n.value().equals("") && p.nonTerminal.equals(getName()))))
+                return buildSequence(p)!=null;
+
+            return false;
+        }
+        public int[] buildSequence(Production p, String[] names, arg[] argtags) {
+            int argTagged = 0;
+            for(int i=0; i<argtags.length; i++)
+                if (argtags[i] != null)
+                    argTagged++;
+
+            // FIXME: can be smarter here
+            if (names.length==p.count) {
+                int[] ret = new int[p.count];
+                for(int i=0; i<p.count; i++) ret[i] = i;
+                return ret;
+            } else if (argTagged==p.count) {
+                int[] ret = new int[argtags.length];
+                int j = 0;
+                for(int i=0; i<argtags.length; i++)
+                    ret[i] = argtags[i]==null ? -1 : (j++);
+                return ret;
+            } else {
+                return null;
+            }
+        }
+        public Sequence makeSequence(Production p) {
+            return Sequence.rewritingSequence(new TargetReducer(p), p.elements, p.labels, p.drops);
+        }
+        public abstract Object plant(Object[] fields, int[] map);
+        public class TargetReducer implements Reducer {
+            private Production p;
+            private int[] map;
+            public TargetReducer(Production p) {
+                this.p = p;
+                this.map = buildSequence(p);
+            }
+            public String toString() { return "reducer-"+Target.this; }
+            public Object reduce(Tree t) {
+                Object[] objects = new Object[t.numChildren()];
+                for(int i=0; i<t.numChildren(); i++) {
+                    Tree tc = t.child(i);
+                    if (tc.head() != null && tc.head() instanceof Reducer)
+                        objects[i] = ((Reducer)tc.head()).reduce(tc);
+                    else if (tc.numChildren() == 0)
+                        objects[i] = tc.head();
+                    else {
+                        System.err.println("FIXME: don't know what to do about " + tc);
+                        objects[i] = null;
+                    }
+                }
+                System.err.println("input tree: " + t);
+                return plant(objects, map);
+            }
+        }
+    }
+
+    public static interface Reducer {
+        public Object reduce(Tree t);
+    }
+
+    public static class TargetClass extends Target {
+        public final Class _class;
+        public TargetClass(Class _class) { this._class = _class; }
+        public String getName() { return _class.getSimpleName(); }
+        public tag getTag() { return (tag)_class.getAnnotation(tag.class); }
+        public nonterminal getNonTerminal() { return (nonterminal)_class.getAnnotation(nonterminal.class); }
+        public String toString() { return _class.getSimpleName(); }
+        public int[] buildSequence(Production p) {
+            Field[]  f       = _class.getDeclaredFields();
+            String[] names   = new String[f.length];
+            arg[]    argtags = new arg[f.length];
+            for(int i=0; i<f.length; i++) {
+                names[i]   = f[i].getName();
+                argtags[i] = f[i].getAnnotation(arg.class);
+            }
+            int[] ret = buildSequence(p, names, argtags);
+            if (ret!=null) return ret;
+            for(Constructor c : _class.getConstructors())
+                if (new TargetConstructor(c).buildSequence(p)!=null)
+                    return new TargetConstructor(c).buildSequence(p);
+            return null;
+        }
+        public Object plant(Object[] fields, int[] map) {
+            try {
+                Object ret = _class.newInstance();
+                Field[] f = _class.getFields();
+                int j = 0;
+                for(int i=0; i<f.length; i++)
+                    if (map[i] != -1) {
+                        Object tgt = Reflection.lub(fields[map[i]]);
+                        if (f[i].getType() == String.class) tgt = stringify(tgt);
+                        // FUGLY
+                        tgt = coerce(tgt, f[i].getType());
+                        System.err.println("setting a " + f[i].getType().getName() + " to " + Reflection.show(tgt));
+                        f[i].set(ret, tgt);
+                    }
+                return ret;
+            } catch (Exception e) {
+                e.printStackTrace();
+                throw new RuntimeException(e);
+            }
+        }
+    }
+
+    public static String stringify(Object o) {
+        if (o==null) return "";
+        if (!(o instanceof Object[])) return o.toString();
+        Object[] arr = (Object[])o;
+        StringBuffer ret = new StringBuffer();
+        for(int i=0; i<arr.length; i++)
+            ret.append(arr[i]);
+        return ret.toString();
+    }
+
+    public static class TargetConstructor extends Target {
+        public final Constructor _ctor;
+        public TargetConstructor(Constructor _ctor) { this._ctor = _ctor; }
+        public String getName() { return _ctor.getName(); }
+        public tag getTag() { return (tag)_ctor.getAnnotation(tag.class); }
+        public nonterminal getNonTerminal() { return (nonterminal)_ctor.getAnnotation(nonterminal.class); }
+        public String toString() { return _ctor.getName(); }
+        public int[] buildSequence(Production p) {
+            Annotation[][] annotations = _ctor.getParameterAnnotations();
+            int len = annotations.length;
+            int ofs = 0;
+            String name = _ctor.getDeclaringClass().getName();
+            /*
+            if (name.indexOf('$') > name.lastIndexOf('.')) {
+                len--;
+                ofs++;
+            }
+            */
+            String[] names   = new String[len];
+            arg[]    argtags = new arg[len];
+            for(int i=0; i<names.length; i++)
+                for(Annotation a : annotations[i+ofs])
+                    if (a instanceof arg)
+                        argtags[i+ofs] = (arg)a;
+            return buildSequence(p, names, argtags);
+        }
+        public Object plant(Object[] fields, int[] map) {
+            try {
+                Class[] argTypes = _ctor.getParameterTypes();
+                Object[] args = new Object[argTypes.length];
+                int j = 0;
+                for(int i=0; i<args.length; i++)
+                    if (map[i] != -1) {
+                        Object tgt = Reflection.lub(fields[map[i]]);
+                        if (argTypes[i] == String.class) tgt = stringify(tgt);
+                        // FUGLY
+                        tgt = coerce(tgt, argTypes[i]);
+                        System.err.println("setting a " + argTypes[i].getName() + " to " + Reflection.show(tgt));
+                        args[i] = tgt;
+                    }
+                return _ctor.newInstance(args);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+    public static class TargetMethod extends Target {
+        public final Method _method;
+        public TargetMethod(Method _method) { this._method = _method; }
+        public String getName() { return _method.getName(); }
+        public String toString() { return _method.getName(); }
+        public tag getTag() { return (tag)_method.getAnnotation(tag.class); }
+        public nonterminal getNonTerminal() { return (nonterminal)_method.getAnnotation(nonterminal.class); }
+        public int[] buildSequence(Production p) {
+            Annotation[][] annotations = _method.getParameterAnnotations();
+            String[] names   = new String[annotations.length];
+            arg[]    argtags = new arg[annotations.length];
+            for(int i=0; i<names.length; i++)
+                for(Annotation a : annotations[i])
+                    if (a instanceof arg)
+                        argtags[i] = (arg)a;
+            int[] ret = buildSequence(p, names, argtags);
+            return ret;
+        }
+        public Object plant(Object[] fields, int[] map) {
+            try {
+                Class[] argTypes = _method.getParameterTypes();
+                Object[] args = new Object[argTypes.length];
+                int j = 0;
+                for(int i=0; i<args.length; i++)
+                    if (map[i] != -1) {
+                        Object tgt = Reflection.lub(fields[map[i]]);
+                        if (argTypes[i] == String.class) tgt = stringify(tgt);
+                        // FUGLY
+                        tgt = coerce(tgt, argTypes[i]);
+                        System.err.println("setting a " + argTypes[i].getName() + " to " + Reflection.show(tgt));
+                        args[i] = tgt;
+                    }
+                System.err.println("invoking " + _method + " with " + Reflection.show(args));
+                return _method.invoke(null, args);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+
+    public static Object coerce(Object o, Class c) {
+        if (o==null) return null;
+        if (c.isInstance(o)) return o;
+        if (c == char.class) {
+            return o.toString().charAt(0);
+        }
+        if (c.isArray() && (c.getComponentType().isInstance(o))) {
+            Object[] ret = (Object[])Array.newInstance(c.getComponentType(), 1);
+            ret[0] = o;
+            return ret;
+        }
+        if (o.getClass().isArray() && c.isArray()) {
+            boolean ok = true;
+            for(int i=0; i<((Object[])o).length; i++) {
+                Object ob = (((Object[])o)[i]);
+                if (ob != null) {
+                    System.err.println("no hit with " + c.getComponentType().getName() + " on " + Reflection.show(((Object[])o)[i]));
+                    ok = false;
+                }
+            }
+            if (ok) {
+                System.err.println("hit with " + c.getComponentType().getName());
+                return Array.newInstance(c.getComponentType(), ((Object[])o).length);
+            }
+        }
+        return o;
+    }
+
+    public static class MG {
+        public static @tag("grammar") class Grammar {
+            public NonTerminal get(String s) {
+                for(NonTerminal nt : nonterminals)
+                    if (nt.name.equals(s))
+                        return nt;
+                return null;
+            }
+            public @arg("NonTerminal") NonTerminal[] nonterminals;
+            public String toString() {
+                String ret = "[ ";
+                for(NonTerminal nt : nonterminals) ret += nt + ", ";
+                return ret + " ]";
+            }
+        }
+        public abstract static class Un extends El {
+            public Seq[][] sequences;
+            public void build(Context cx, Union u) {
+                HashSet<Sequence> bad2 = new HashSet<Sequence>();
+                for(int i=0; i<sequences.length; i++) {
+                    Seq[] group = sequences[i];
+                    Union u2 = new Union();
+                    if (sequences.length==1) u2 = u;
+                    for(int j=0; j<group.length; j++) {
+                        group[j].build(cx, u2, false);
+                    }
+                    if (sequences.length==1) break;
+                    Sequence seq = Sequence.singleton(u2);
+                    for(Sequence s : bad2) {
+                        s.lame = true;
+                        seq = seq.not(s);
+                    }
+                    u.add(seq);
+                    bad2.add(Sequence.singleton(u2));
+                }
+            }
+        }
+        public static class NonTerminal extends Un {
+            public String  name = null;
+            public @nonterminal("NonTerminal") NonTerminal(@arg("Word") String name,
+                                                           @arg("RHS") Seq[][] sequences) {
+                this.name = name;
+                this.sequences = sequences;
+            }
+            public Element build(Context cx) { return cx.get(name); }
+        }
+
+        public static class AnonUn extends Un {
+            public @tag("(") AnonUn(Seq[][] sequences) {
+                this.sequences = sequences;
+            }
+            public Element build(Context cx) {
+                Union ret = new Union();
+                build(cx, ret);
+                return ret;
+            }
+        }
+
+        //public static @tag void range(char c) { }
+        public static class Range {
+            public @tag("range") Range(char only) { first = only; last = only; }
+            public @tag("-")     Range(char first, char last) { this.first = first; this.last = last; }
+            public char first;
+            public char last;
+        }
+        public static abstract class El {
+            public String getLabel() { return null; }
+            public String getOwnerTag() { return null; }
+            public boolean drop() { return false; }
+            public abstract Element build(Context cx);
+        }
+        public static class Drop extends El {
+            public El e;
+            public Drop(El e) { this.e = e; }
+            public String getLabel() { return null; }
+            public boolean drop() { return true; }
+            public String getOwnerTag() { return e.getOwnerTag(); }
+            public Element build(Context cx) { return e.build(cx); }
+        }
+        public static class Label extends El {
+            public String label;
+            public El e;
+            public Label(String label, El e) { this.e = e; this.label = label; }
+            public String getLabel() { return label; }
+            public String getOwnerTag() { return e.getOwnerTag(); }
+            public Element build(Context cx) { return e.build(cx); }
+        }
+        public static /*abstract*/ class Seq {
+            HashSet<Seq> and = new HashSet<Seq>();
+            HashSet<Seq> not = new HashSet<Seq>();
+            El[] elements;
+            El follow;
+            String tag = null;
+            boolean lame;
+            public Seq(El e) { this(new El[] { e }); }
+            public Seq(El[] elements) { this.elements = elements; }
+            public Seq tag(String tag) { this.tag = tag; return this; }
+            public Seq follow(El follow) { this.follow = follow; return this; }
+            public Seq dup() {
+                Seq ret = new Seq(elements);
+                ret.and.addAll(and);
+                ret.not.addAll(not);
+                ret.follow = follow;
+                ret.tag = tag;
+                return ret;
+            }
+            public Seq and(Seq s) { and.add(s); s.lame = true; return this; }
+            public Seq andnot(Seq s) { not.add(s); s.lame = true; return this; }
+            public Seq separate(El sep) {
+                El[] elements = new El[this.elements.length * 2 - 1];
+                for(int i=0; i<this.elements.length; i++) {
+                    elements[i*2]   = this.elements[i];
+                    if (i<this.elements.length-1)
+                        elements[i*2+1] = new Drop(sep);
+                }
+                this.elements = elements;
+                return this;
+            }
+            public Sequence build(Context cx, Union u, boolean lame) {
+                Sequence ret = build0(cx, lame || this.lame);
+                for(Seq s : and) { Sequence dork = s.build(cx, u, true); ret = ret.and(dork); }
+                for(Seq s : not) { Sequence dork = s.build(cx, u, true); ret = ret.not(dork); }
+                u.add(ret);
+                ret.lame = lame;
+                return ret;
+            }
+            public Sequence build0(Context cx, boolean lame) {
+                boolean unwrap = false;
+                boolean dropAll = lame;
+                if (tag!=null && tag.equals("[]")) unwrap  = true;
+                if (tag!=null && "()".equals(tag)) dropAll = true;
+                Object[] labels = new Object[elements.length];
+                boolean[] drops = new boolean[elements.length];
+                Element[] els = new Element[elements.length];
+                for(int i=0; i<elements.length; i++) {
+                    labels[i] = elements[i].getLabel();
+                    drops[i]  = elements[i].drop();
+                    els[i] = elements[i].build(cx);
+                    if (elements[i].getOwnerTag() != null)
+                        tag = elements[i].getOwnerTag();
+                }
+                Sequence ret = null;
+                if (dropAll)     ret = Sequence.drop(els, false);
+                else if (unwrap) ret = Sequence.unwrap(els, cx.rm.repeatTag(), drops);
+                else if (tag!=null) {
+                    ret = cx.rm.resolveTag(tag, cx.cnt, els, labels, drops);
+                } else {
+                    int idx = -1;
+                    for(int i=0; i<els.length; i++)
+                        if (!drops[i])
+                            if (idx==-1) idx = i;
+                            else throw new Error("multiple non-dropped elements in sequence: " + Sequence.drop(els,false));
+                    if (idx != -1) ret = Sequence.singleton(els, idx);
+                    else           ret = Sequence.drop(els, false);
+                }
+                if (this.follow != null)
+                    ret.follow = MetaGrammar.infer(this.follow.build(cx));
+                ret.lame = this.lame;
+                return ret;
+            }
+        }
+        public static @tag("&")   Seq  and(Seq s,         El[] elements) { return s.and(seq(elements)); }
+        public static @tag("&~")  Seq  andnot(Seq s,      El[] elements) { return s.andnot(seq(elements)); }
+        public static @tag("->")  Seq  arrow(Seq s, El e)                { return s.follow(e); }
+        public static @tag("::")  Seq  tag(String tagname, Seq s)        { return s.tag(tagname); }
+        public static @tag("/")   Seq  slash(Seq s, El e)                { return s.separate(e); }
+
+        public static @tag("ps")  Seq  seq(El[] elements)                { return new Seq(elements); }
+        public static @tag        Seq  psx(Seq s)                        { return s; }
+        public static @tag(":")   El   colon(String s, El e)             { return new Label(s, e); }
+        public static @tag(")")   void close(String foo)                 { throw new Error("not supported"); }
+        public static @tag("()")  El   epsilon()                         { return new Constant(Union.epsilon); }
+
+        public static @tag("nonTerminal") class NonTerminalReference extends El {
+            public @arg String nonTerminal;
+            public Element build(Context cx) {
+                return cx.get(nonTerminal);
+            }
+        }
+        public static class StringLiteral        extends Constant {
+            public @tag("literal") StringLiteral(String string) { super(CharRange.string(string)); }
+            public boolean drop() { return true; }
+        }
+        public static                     class CharClass            extends El {
+            Range[] ranges;
+            public @tag("[") CharClass(Range[] ranges) { this.ranges = ranges; }
+            public Element build(Context cx) {
+                edu.berkeley.sbp.util.Range.Set set = new edu.berkeley.sbp.util.Range.Set();
+                for(Range r : ranges)
+                        set.add(r.first, r.last);
+                return CharRange.set(set);
+            }
+        }
+
+        public static @tag("{")           class Tree                 extends El {
+            public @arg Seq body;
+            public Element build(Context cx) {
+                throw new Error();
+            }
+        }
+
+        public static class Rep extends El {
+            public El e, sep;
+            public boolean zero, many, max;
+            public Rep(El e, El sep, boolean zero, boolean many, boolean max) {
+                this.e = e; this.sep = sep; this.zero = zero; this.many = many; this.max = max;}
+            public Element build(Context cx) {
+                return (!max)
+                    ? Sequence.repeat(e.build(cx),        zero, many, sep==null ? null : sep.build(cx), cx.rm.repeatTag())
+                    : sep==null
+                    ? Sequence.repeatMaximal(MetaGrammar.infer(e.build(cx)), zero, many,                                   cx.rm.repeatTag())
+                    : Sequence.repeatMaximal(e.build(cx),                    zero, many, MetaGrammar.infer(sep.build(cx)), cx.rm.repeatTag());
+            }
+        }
+        public static class Constant extends El {
+            Element constant;
+            public Constant(Element constant) { this.constant = constant; }
+            public Element build(Context cx) { return constant; }
+        }
+        public abstract static class PostProcess extends El {
+            El e;
+            public PostProcess(El e) { this.e = e; }
+            public Element build(Context cx) { return postProcess(e.build(cx)); }
+            public abstract Element postProcess(Element e);
+        }
+
+        // FIXME: it would be nice if we could hoist this into "Rep"
+        public static @tag("++")  El plusmax(final El e)                     { return new Rep(e, null, false, true, true); }
+        public static @tag("+")   El plus(final El e)                        { return new Rep(e, null, false, true, false); }
+        public static @tag("++/") El plusmaxfollow(final El e, final El sep) { return new Rep(e, sep,  false, true, true); }
+        public static @tag("+/")  El plusfollow(final El e, final El sep)    { return new Rep(e, sep,  false, true, false); }
+        public static @tag("**")  El starmax(final El e)                     { return new Rep(e, null, true,  true, true); }
+        public static @tag("*")   El star(final El e)                        { return new Rep(e, null, true,  true, false); }
+        public static @tag("**/") El starmaxfollow(final El e, final El sep) { return new Rep(e, sep,  true,  true, true); }
+        public static @tag("*/")  El starfollow(final El e, final El sep)    { return new Rep(e, sep,  true,  true, false); }
+        public static @tag("?")   El question(final El e)                    { return new Rep(e, null, true,  true, false); }
+
+        public static @tag("!")   El bang(final El e)                        { return new Drop(e); }
+
+        public static @tag("^")   El caret(final String s) {
+            return new Drop(new Constant(CharRange.string(s)) {
+                    public String getOwnerTag() { return s; }
+                });
+        }
+
+        public static @tag("~")   El tilde(final El e) {
+            return new PostProcess(e) {
+                    public Element postProcess(Element e) {
+                        return MetaGrammar.infer((Topology<Character>)Atom.toAtom(e).complement()); 
+                    } }; }
+
+        public static @tag("^^")  void doublecaret(final El e)                 { throw new Error("not implemented"); }
+
+        //public static @tag("(")   El subexpression(Seq[][] rhs)                { return new NonTerminal(rhs); }
+
+        public static @nonterminal("Word")    String word(String s) { return s; }
+        public static @nonterminal("Quoted")  String quoted(String s) { return s; }
+        public static @nonterminal("escaped") String c(char c) { return c+""; }
+        public static @tag("\"\"")            String emptystring() { return ""; }
+        public static @tag("\n")              String retur() { return "\n"; }
+        public static @tag("\r")              String lf() { return "\r"; }
+
+    }
+    public static class Context {
+        HashMap<String,Union> map = new HashMap<String,Union>();
+        private MG.Grammar grammar;
+        public String cnt = null;
+        private ReflectiveMeta rm;
+        public Context(MG.Grammar g, ReflectiveMeta rm) {
+            this.grammar = g;
+            this.rm = rm;
+        }
+        public Union build() {
+            Union ret = null;
+            for(MG.NonTerminal nt : grammar.nonterminals) {
+                Union u = get(nt.name);
+                if ("s".equals(nt.name))
+                    ret = u;
+            }
+            return ret;
+        }
+        public Context(Tree t, ReflectiveMeta rm) {
+            this.rm = rm;
+            Reducer red = (Reducer)t.head();
+            this.grammar = (MG.Grammar)red.reduce(t);
+        }
+        public Union peek(String name) { return map.get(name); }
+        public void  put(String name, Union u) { map.put(name, u); }
+        public Union get(String name) {
+            Union ret = map.get(name);
+            if (ret != null) return ret;
+            ret = new Union(name);
+            map.put(name, ret);
+            MG.NonTerminal nt = grammar.get(name);
+            if (nt==null) {
+                System.err.println("*** warning could not find " + name);
+            } else {
+                String old = cnt;
+                cnt = name;
+                nt.build(this, ret);
+                cnt = old;
+            }
+            return ret;
+        }
+
     }
 }