4.3BSD - /usr/src/new/icon/lib/escan.c

   1: #include "../h/rt.h"
   2: 
   3: /*
   4:  * escan - restore &subject and &pos at the end of a scanning expression.
   5:  *
   6:  *  Arguments:
   7:  *    arg1 - value being scanned
   8:  *    arg2 - old value of &subject
   9:  *    arg3 - old value of &pos
  10:  *    arg4 - result of the scanning expression
  11:  *
  12:  * The result of the scanning expression is dereferenced if it refers to &subject
  13:  *  or &pos, then copied to the first argument (the last three will
  14:  *  be popped when escan returns).  Then the previous values of &subject
  15:  *  and &pos are restored.
  16:  *
  17:  * Escan suspends once it has restored the old &subject; on failure
  18:  *  the new &subject and &pos are "unrestored", and the failure is
  19:  *  propagated into the using clause.
  20:  */
  21: 
  22: escan(nargs, arg4, arg3, arg2, arg1)
  23: int nargs;
  24: struct descrip arg4, arg3, arg2, arg1;
  25:    {
  26:    DclSave
  27:    struct descrip tmp;
  28: 
  29:    SetBound;
  30: 
  31:    /*
  32:     * If the result of the scanning expression is &subject or &pos,
  33:     *  it is dereferenced.
  34:     */
  35:    if (arg4.type == D_VAR && (int)BLKLOC(arg1) == (int)&k_subject)
  36:       DeRef(arg4)
  37:    if (arg4.type == D_TVPOS)
  38:       DeRef(arg4)
  39: 
  40:    /*
  41:     * Copy the result of the scanning expression into arg1, which will
  42:     *  be the result of the scan.
  43:     */
  44:    arg1 = arg4;
  45: 
  46:    /*
  47:     * Swap new and old values of &subject, leaving the new value in arg2.
  48:     */
  49:    tmp = k_subject;
  50:    k_subject = arg2;
  51:    arg2 = tmp;
  52: 
  53:    /*
  54:     * Swap new and old values of &pos, leaving the new value in arg3.
  55:     */
  56:    tmp = arg3;
  57:    INTVAL(arg3) = k_pos;
  58:    k_pos = INTVAL(tmp);
  59: 
  60:    /*
  61:     * Suspend the value of the scanning expression.
  62:     */
  63:    suspend();
  64: 
  65:    /*
  66:     * Upon resumption, restore the new values for &subject and &pos
  67:     *  and fail.
  68:     */
  69:    k_subject = arg2;
  70:    k_pos = INTVAL(arg3);
  71: 
  72:    fail();
  73:    }

Defined functions