scm.Env Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of jasmin Show documentation
Java Assembler Interface for the Soot framework
There is a newer version: 3.0.3
package scm;

                                // an environment for the underlying
                                // evaluator

import java.util.*;

class Env
{
  Hashtable bindings=null;      // bindings are lazily created
                                // during a set variable
  static Object MAGIC_KLUDGE="**jas-nil-internal";
                                // record "null" as this.

  Env parent;

  Obj lookup(Symbol cvar)
  {
    Object ret;
    Env f;
    Hashtable b;

    for (f=this, ret=null, b=bindings;
         (ret == null) && (f != null);
         f = f.parent)
      {
        b = f.bindings;
        if (b != null) { ret = b.get(cvar); }
      }
    if (ret == null)
      { throw new SchemeError("Unbound variable " + cvar); }
    if (ret == MAGIC_KLUDGE)
      return null;
    else
      return ((Obj)ret);
  }

  void setvar(Symbol cvar, Obj val)
  {
    Object ret;
    Env f;
    Hashtable b;

    for (f=this, ret=null, b=bindings;
         (ret == null) && (f != null);
         f = f.parent)
      {
        b = f.bindings;
        if (b != null) { ret = b.get(cvar); }
      }
    if (ret == null)
      { throw new SchemeError("Attempted to set unbound variable " + cvar); }
    if (val == null)
      { b.put(cvar, MAGIC_KLUDGE); }
    else
      { b.put(cvar, val); }
  }

  void definevar(Symbol v, Obj val)
  {
    if (bindings == null) bindings = new Hashtable();
    if (val == null)
      { bindings.put(v, MAGIC_KLUDGE); }
    else
      { bindings.put(v, val); }
  }

  Env extendenv(Cell formals, Cell params)
  {
    Symbol thissym; Obj thisval;
    Env ret = new Env();

    ret.parent = this;
    if (formals == null)
      {
        if (params != null)
          { throw new SchemeError("mismatched arglist to entend env"); } }
    else
      {
        ret.bindings = new Hashtable();
        while (formals != null)
          {
            thissym = (Symbol) formals.car;
            thisval = params.car;
            if (thisval == null)
              {ret.bindings.put(thissym, MAGIC_KLUDGE);}
            else
              {ret.bindings.put(thissym, thisval);}
            formals = formals.cdr;
            params =  params.cdr;
          }
        if (params != null)
          { throw new SchemeError("mismatched arglist to extend env"); } }
    return ret;
  }
  public String toString()
  {
    String ret;

    return ("Binding is " + bindings + "\nparent is " + parent);
  }
}