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5.1.29 eval

Syntax:
eval ( expression )
Type:
none
Purpose:
evaluates (quoted) expressions. Within a quoted expression, the quote can be "undone" by an eval (i.e., each eval "undoes" the effect of exactly one quote). Used only when receiving a quoted expression from an ssi link, with quote and write to prevent local evaluations when writing to an ssi link.
Example:
 
  link l="ssi:w example.ssi";
  ring r=0,(x,y,z),ds;
  ideal i=maxideal(3);
  ideal j=x7+x3,x2,z;
  // compute i+j before writing, but not std
  // this writes 'std(ideal(x3,...,z))'
  write (l, quote(std(eval(i+j))));
  option(prot);
  close(l);
  // now read it in again and evaluate
  // read(l) forces to compute 'std(ideal(x3,...,z))'
  read(l);
==> _[1]=z
==> _[2]=x2
==> _[3]=xy2
==> _[4]=y3
  close(l);
See Ssi links; quote; write.