You need to use == for comparisons. Your current code is trying to set the length property which is readonly, hence the error

list,recursion,prolog,sublist,variable-length

Something similar to this is what you might be looking for mylen([H|Lc],N) :- X is mod(H,2), X == 0, mylen(Lc,M), N is M+1. mylen([],0). mylen([H|Lc],N) :- mylen(Lc, M), N = M. ...

Assuming your ID is character, and you don't consider blanks digits: if lengthn(id) ~= 4 then delete; If your ID is numeric: if 1000 <= id <= 9999 then output;...

c#,count,listbox,variable-length

I think that ListBox inherits or implements Enumerable that has an option to return Count the number of elements in the list. The ListBox also has it own method called .Length which has a similar effects but specifically used in the class ListBox If I would have to choose between...

python,arrays,numpy,matplotlib,variable-length

You could use interp1d with kind="nearest". (Using "nearest" will give steps at the boundaries and look like an expansion, but without your needing to do it explicitly, and also do a reasonable approximation to what you want if your lengths don't exactly divide as needed.) This would give something like...

android,onclicklistener,variable-length

Too long for a comment, why don't you check your strings and then set them based on their length if they aren't empty. String firstString = firstnumET.getText().toString(); firstNum = (firstString.trim().equals(""))? 0: firstString.length(); String secondString = secondnumET.getText().toString(); secondNum = (secondString.trim().equals(""))? 0: secondString.length(); ansTV.setText("" + (secondString + firstString)); You could obviously make...

algorithm,iteration,combinations,permutation,variable-length

Here's another iterative solution: You can create an array of integers of size K to act as a counter recording how far you are through the combinations, and a char array to store the current combination. After printing each one, move on to the next combination by increasing one of...

c++,qt,file,buffer,variable-length

Pointers don't know its allocated size. You may use std::vector which keep track of size for you: std::vector<char> pStartBuffer(MyHeader.u32Size); memcpy(pStartBuffer, &MyHeader, MyHeader.u32Size); And latter: file.write(pStartBuffer.data(), pStartBuffer.size()); ...

vector,glsl,opengl-3,variable-length

The problem is exactly what the error message says: Illegal vector field selection length The only line where you try to use length as a field selector is this one (line break added): float cosine = dot(cameraSpacePosition, cameraSpaceNormal) / (cameraSpacePosition.length * cameraSpaceNormal.length); This usage of length is invalid. There are...