The gp2c compiler can also be used to find errors in GP programs. For that we should use the -W option like in
./gp2c -W pari/examples/squfof.gp > squfof.gp.c
Warning:pari/examples/squfof.gp:7:variable undeclared p Warning:pari/examples/squfof.gp:11:variable undeclared dd Warning:pari/examples/squfof.gp:11:variable undeclared d Warning:pari/examples/squfof.gp:11:variable undeclared b ... Warning:pari/examples/squfof.gp:45:variable undeclared b1
This lists variables that are used but not declared. It is important
to declare all your variables with local(), or with global().
For gp2c, undeclared variables are taken to be ``formal variables'' for
polynomials. For example if you write a function to build a second degree
polynomial like
pol(a,b,c)=a*x^2+b*x+c
you must not declare 'x' here, since it stands for the formal variable x.