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);