BlockExp


1   // Copyright (c) 1999, 2006  Per M.A. Bothner.
2   // This is free software;  for terms and warranty disclaimer see ./COPYING.
3   
4   package gnu.expr;
5   import gnu.bytecode.*;
6   import gnu.mapping.*;
7   
8   /**
9    * Class used to implement a block that can be exited.
10   * @author  Per Bothner
11   */
12  
13  public class BlockExp extends Expression
14  {
15    Declaration label;
16    Expression body;
17  
18    /** If non-null, evaluate this, but only if non-normal exit. */
19    Expression exitBody;
20  
21    public void setBody(Expression body)
22    {
23      this.body = body;
24    }
25  
26    public void setBody(Expression body, Expression exitBody)
27    {
28      this.body = body;
29      this.exitBody = exitBody;
30    }
31  
32    /* Target used to evaluate body. Temporary only used during compilation. */
33    Target subTarget;
34    /* Label to exit to.  Temporary only used during compilation. */
35    Label exitLabel;
36    /* Current TryState when we start compiling the.  Temporary. */
37    TryState oldTryState;
38  
39    protected boolean mustCompile () { return false; }
40  
41    public void apply (CallContext ctx) throws Throwable  
42    {
43      Object   result;
44      try
45        {
46          result = body.eval(ctx);
47        }
48      catch (BlockExitException ex)
49        {
50          if (ex.exit.block != this)
51            throw ex;
52          result = ex.exit.result;
53          if (exitBody != null)
54            result = exitBody.eval(ctx);
55        }
56      ctx.writeValue(result);
57    }
58  
59    public void compile (Compilation comp, Target target)
60    {
61      Target subTarget;
62      if (target instanceof IgnoreTarget
63      || target == Target.pushObject)
64        subTarget = target;
65      else
66        {
67      // We can probably do better - and this is probably
68      // wrong for TailTargets.  FIXME.
69      subTarget = new StackTarget(getType());
70        }
71      gnu.bytecode.CodeAttr code = comp.getCode();
72      oldTryState = code.getCurrentTry();
73      exitLabel = new Label(code);
74      this.subTarget = exitBody == null ? subTarget : Target.Ignore;
75      body.compileWithPosition(comp, subTarget);
76      if (exitBody != null)
77        {
78          Label doneLabel = new Label(code);
79          code.emitGoto(doneLabel);
80          exitLabel.define(code);
81          exitBody.compileWithPosition(comp, subTarget);
82          doneLabel.define(code);
83        }
84      else
85        exitLabel.define(code);
86      if (subTarget != target)
87        target.compileFromStack(comp, subTarget.getType());
88      oldTryState = null;
89    }
90  
91    protected Expression walk (ExpWalker walker)
92    {
93      return walker.walkBlockExp(this);
94    }
95  
96    protected void walkChildren (ExpWalker walker)
97    {
98      body = walker.walk(body);
99      if (walker.exitValue == null && exitBody != null)
100       exitBody = walker.walk(exitBody);
101   }
102 
103   public void print (OutPort out)
104   {
105     out.startLogicalBlock("(Block", ")", 2);
106     if (label != null)
107      out.print(label.getName());
108     out.writeSpaceLinear();
109     body.print(out);
110     if (exitBody != null)
111       {
112     out.writeSpaceLinear();
113         out.print("else ");
114         exitBody.print(out);
115       }
116     out.endLogicalBlock(")");
117   }
118 }
119 
120 class BlockExitException extends RuntimeException  
121 {
122   ExitExp exit;
123   Object   result;
124   public BlockExitException (ExitExp exit, Object   result)
125   {
126     this.exit = exit;
127     this.result = result;
128   }
129 }
130
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