/in/foo.c:1:1: error: unknown type name 'def'
    1 | def is_prime(num):
      | ^~~
/in/foo.c: In function 'is_prime':
/in/foo.c:1:18: error: expected declaration specifiers before ':' token
    1 | def is_prime(num):
      |                  ^
/in/foo.c:1:5: warning: type of 'num' defaults to 'int' [-Wimplicit-int]
    1 | def is_prime(num):
      |     ^~~~~~~~
/in/foo.c:19: warning: control reaches end of non-void function [-Wreturn-type]