Is there a way to handle the content of the \magdecl TEX-variable in METAPOST? (Therion V5.3.16)

In a string or numeric? – I think, i‘ve an syntax problem…

1.) string handling:

string dec;

%dec:=“3.022“; % FINE!

dec:=\magdecl; % ERROR

p_label.top(thTEX(dec),(0,0),0,8); % >> string output

2.) numeric handling:

numeric dec;

%dec:=3.022; % FINE!

dec:=\magdecl; % ERROR

p_label.top(thTEX(decimal dec),(0,0),0,8); % >> numeric to string output