Error -Attempted to write to a constant value?

I’m writing a shader that uses the noise that comes in the example shaders:

#include “stdosl.h”
#include “node_texture.h”

float noise(point p, string basis, float distortion, float detail, float fac, color Color)
{
point r;
int hard = 0;

if (distortion != 0.0) {
r[0] = noise_basis(p + point(13.5), basis) * distortion;
r[1] = noise_basis(p, basis) * distortion;
r[2] = noise_basis(p - point(13.5), basis) * distortion;

  p += r;

}

fac = noise_turbulence(p, basis, detail, hard);

Color = color(fac, noise_turbulence(point(p[1], p[0], p[2]), basis, detail, hard),
noise_turbulence(point(p[1], p[2], p[0]), basis, detail, hard));

return fac;
}

shader node_noise_texture(
int use_mapping = 0,
matrix mapping = matrix(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
float Distortion = 0.0,
float Scale = 5.0,
float Detail = 2.0,
point Vector = P,
output float Fac = 0.0,
output color Color = 0.0)
{
point p = Vector;

if (use_mapping)
p = transform(mapping, p);

string Basis = “Perlin”;
Fac = noise(p * Scale, Basis, Distortion, Detail, Fac, Color);
}

For my purposes, I’ve renamed it “perlinn”.
This line, and I know it’s this line because the shader compiles when I comment it out(I haven’t used the variable yet):

float neb_fac_per = perlinn(n, “Perlin”, 0.0, 16.0, 0, color(0.0, 0.0, 0.0));

gives me the error:

error: Attempted to write to a constant value

I can’t for the life of me figure out why. Can anyone shed some light?
Much appreciated,
DarkCrescent

Okay, I’ve solved it. Turns out the function doesn’t like passing in numbers; you have to pass in variables. Hope this helps somebody!