sub foo { $_[0] + 1 }

##</code><code>##

Always unpack @_ first at line 22, column 1.  See page 178 of PBP.  (Severity: 4)
Subroutine "foo" does not end with "return" at line 22, column 1.  See page 197 of PBP.  (Severity: 4)

##</code><code>##

use Function::Parameters;
fun foo ($x) {
    $x + 1
}

##</code><code>##

use Function::Parameters;
use Types::Standard qw( Num );

fun foo (Num $x) {
    $x + 1
}

##</code><code>##

mmap(NULL, 192512, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe772fdf000
mremap(0x7fe771772000, 532480, 536576, MREMAP_MAYMOVE) = 0x7fe771772000
brk(0x49ac000)                          = 0x49ac000
brk(0x49cd000)                          = 0x49cd000
mremap(0x7fe771772000, 536576, 540672, MREMAP_MAYMOVE) = 0x7fe771772000
brk(0x49ee000)                          = 0x49ee000
brk(0x49ed000)                          = 0x49ed000
brk(0x4a0e000)                          = 0x4a0e000
brk(0x4a2f000)                          = 0x4a2f000
mremap(0x7fe771772000, 540672, 544768, MREMAP_MAYMOVE) = 0x7fe771772000
...