Using version 2.6 of GSL from ftp://ftp.gnu.org/gnu/gsl/gsl-2.6.tar.gz

OS is Ubuntu 18.04.2 LTS

Hardware is a Dell workstation with a 3.60 GHz Intel i7-4790 and 32 GB
of RAM

Compiler is gcc 7.4.0 with the -w option

When the degree of the laguerre polynomial is zero and the second argument
is a NaN, eval_genlaguerre returns 1.0. Despite the fact that the laguerre
polynomial of degree zero evaluates to 1 over its whole domain, the NaN
does not adhere to the domain restriction stated in the docs that the
second argument should be greater than -1.

#include <gsl/gsl_sf.h>
#include <stdio.h>
#include <gsl/gsl_math.h>

int main (void){
double out;
out = gsl_sf_laguerre_n(0, GSL_NAN, 2.2738632088209076);

printf("%f\n", out);
printf("%.21e\n", out);
return 0;
}