lately I tried to develop an interface that will plot the furier sum of a given function up to a given number of terms.

The code is here:

isEven[f_] := SameQ[f[t], f[(-t)]] a[n_, f_] := If[isEven[f], Integrate[f[y]*Cos[n y], {y, -Pi, Pi}], 0] b[n_, f_] := If[isEven[f], 0, Integrate[f[y]*Sin[n y], {y, -Pi, Pi}]] fourier[f_, m_] := Sum[a[n, f]*Cos[n x] + b[n, f]*Sin[n x], {n, 1, m}]  Interpretation[  {g = x^2, min = 0, max = 2 Pi, sum = 5},  Panel[     Grid[{{Style["Furier Series", Bold], SpanFromLeft},             {"Function:", InputField[Dynamic[g]]},             {"Min:", InputField[Dynamic[min]]},             {"Max:", InputField[Dynamic[max]]},             {"Sum:", InputField[Dynamic[sum]]}}]   ],  Plot[Evaluate[fourier[g[x], sum]], {x, min, max}]] 

The first part specifies the functions I would need, and the second part is an inteface to use the tool.

When i run the code, a keep getting these errors:

And then gives me an empty plot.

Does anyone here know what is the problem?

Thanks a lot!