Function: mapget
Section: programming/specific
C-Name: mapget
Prototype: GG
Help: mapget(M,x): returns the image of x by the map M.
Doc: Returns the image of $x$ by the map $M$.
 \bprog
 ? M=Map(["a",23;"b",43]);
 ? mapget(M,"a")
 %2 = 23
 ? mapget(M,"b")
 %3 = 43
 @eprog\noindent Raises an exception when the key $x$ is not present in $M$.
 \bprog
 ? mapget(M,"c")
   ***   at top-level: mapget(M,"c")
   ***                 ^-------------
   *** mapget: non-existent component in mapget: index not in map
 @eprog
