git checkout -b tuto-first

vi src/test/in/interval
interval(1,0) == []

./Configure -l
make test-interval
vi Olinux-x86_64/interval-sta.dif

vi src/functions/linear_algebra/interval

Function: interval
Section: linear_algebra
C-Name: interval
Prototype: GG
Help: interval(a,b): return the integer interval [a..b].
Doc: Return the integer interval~$\{a,a+1,\dots,b\}$. Empty if~$b<a$.

make gp

vi src/headers/paridecl.h

/* interval.c */
GEN     interval(GEN a, GEN b);

vi src/basemath/interval.c

#include "pari.h"
#include "paripriv.h"

GEN interval(GEN a, GEN b)
{
  pari_sp av = avma;
  return gc_GEN(av, gen_0);
}

./Configure -l
make gp
./gp
interval(1,0)
make test-interval

type(interval(1,0))=="t_VEC"

  GEN v;
  v = cgetg(1, t_VEC);
  return gc_GEN(av, v);

interval(0,1) == [0,1]

  long n;
  n = itos(subii(b,a))+1;
  if(n<0) n=0;
  v = cgetg(n+1, t_VEC);

  long n, i;
  gel(v,1) = a;
  for (i=2; i<=n; i++) gel(v,i) = addis(gel(v,i-1),1);