I'm getting error when I use conditional operation

Question

I've written a line using a conditional operator as shown below:

assign {RS2, RS1} = (!DisM || !DisX)? (RdEn==2'b00? (!DisI? {rs2, rs1} : 64'bz) : (RdEn==2'b01? (!switch? {rs2, Rn} : {Rn, rs1}) : {Rm, Rn}))) : 64'bz;

1. RS2 & RS1 are 32 bit output wires.
2. Rn & Rm are 32 bit inputs.
3. rs1 & rs2 are 32 bit registers.
4. RdEn is 2bit register.
5. DisI and switch are one bit register.

The simulator (Icarus 0.9.7 or any) is showing there is a syntax error in the above line.

Here is my code which addresses the same problem:

module TEST(Rn, Rm, DisM, DisX, DisI, switch, RdEn, RS1, RS2);
input [31:0]Rn, Rm;
input DisM, DisX, DisI, switch;
input [1:0]RdEn;
output [31:0]RS1, RS2;

reg [31:0]rs1, rs2;

always@*
begin
    rs1 = Rn + 32'd7;
    rs2 = Rm - 32'd7;
end

assign {RS2, RS1} = (!DisM || !DisX)? (RdEn==2'b00? (!DisI? {rs2, rs1} : {64{1'bz}}) : (RdEn==2'b01? (!switch? {rs2, Rn} : {Rn, rs1}) : {Rm, Rn}))) : {64{1'bz}};

endmodule

Answer 1

The compiler interpreted the ? in RdEn==2'b00? as a 3rd bit instead of as the ternary operator. Just add a space between b00 and ?. Same for b01?.

? is a valid z_digit. Refer to IEEE Std 1800-2012, section 5.7 Numbers.

Also, you had a mismatched number of parentheses (a good editor can show this):

assign {RS2, RS1} = (!DisM || !DisX)? (RdEn==2'b00 ? (!DisI? {rs2, rs1} : {64{1'bz}}) : (RdEn==2'b01 ? (!switch? {rs2, Rn} : {Rn, rs1}) : {Rm, Rn})) : {64{1'bz}};

It is also good practice to use {64{1'bz}} to make sure you get 64 bits of 1'bz.