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TopLevel --
make a top-level variable accessible inside a function
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TopLevel X;
where X is the name of a top-level variable or function.
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This command makes a top-level variable accessible from inside a
function. For instance, it is useful for making the rings
QQ
and
ZZ
accessible, and also if a top-level function is to be passed as
a parameter (e.g. to the function
SortBy
). It is poor style to
use
TopLevel for purposes other than these.
A fully qualified package variable can be used directly in a function;
the
TopLevel command is
not needed in this case (and gives an
error if a fully qualified package name is specified).
See also the commands
ImportByRef, ImportByValue
if you want to
access a non-top-level variable inside an anonymous function.
/**/ define BeautifulRing(N)
/**/ TopLevel QQ;
/**/ R ::= QQ[b,e,a,u,t,y];
/**/ return R;
/**/ enddefine;
/**/ define CompareLen(X,Y) return len(X) < len(Y); EndDefine;
/**/
/**/ define LongestName(ListOfNameAndValue)
/**/ TopLevel CompareLen; --> to pass it as paremeter to SortBy
/**/ names := [entry[1] | entry in ListOfNameAndValue];
/**/ SortBy(ref names, CompareLen);
/**/ return last(names);
/**/ EndDefine;
/**/
/**/ L := [["ABC",1],["XYZT",2]];
/**/ LongestName(L);
XYZT
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