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showChessPosition[fen_String]:=(*beginwiththefenposition*)fen//(*extracttheboardrepresentation*)Part[StringSplit[#],1]&//(*splitintorowsusingtotheslashdelimiter*)StringSplit[#,"/"]&//(*replacepiecesnameswithunicodeequivalentcharacters*)StringReplace#,"K""♔","Q""♕","R""♖","B""♗","N""♘","P""♙","k""♚","q""♛","r""♜","b""♝","n""♞","p""♟"&//(*splitintocharacters*)Characters//(*replacedigitsbythecorrespondingnumbersofemptysetcharacters*)#//.{n_StringToExpression[n]/;DigitQ[n],n_IntegerSplice[ConstantArray["∅",n]]}&//(*Flatten*)Flatten//(*rifflecoordinates*)Riffle[#,Reverse/@Tuples[{Range[8,1,-1],Range[8]}]]&//(*partitionintwo*)Partition[#,2]&//(*filteremptysquaresout*)Cases[#,{Except["∅"],__}]&//(*turnintoText*)#/.{p_String,coord__}Text[Style[p,FontSize24],{-.5,-.5}+coord]&//(*turnintoGraphics*)Graphics@#&//(*overlayanemptychessboard(usinghttps://mathematica.stackexchange.com/questions/58690/how-to-build-a-game-board)*)Show[{MatrixPlot[Table[Mod[i+j,2],{i,8},{j,8}],ColorFunctionGrayLevel,FrameTicks{{#,#}&@Table[{i,8-i+1,0},{i,8}],{#,#}&@Table[{i,FromCharacterCode[ToCharacterCode["a"]+i-1],0},{i,8}]}],#}]&
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showChessPosition@"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
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