Functions.php

<?php

class Functions {
  public static function getScope() {   
    // Here I had to instantiate the class twice, or the static method would not be callable (???)
    return ['Functions\Inner' => new \Functions\Inner((new \Function\Inner([]))::getScope()) ]; 
  }
  public function __construct($scope) {
    if ($scope !== []) {
      $this->scope = $scope;
      $this->foo = self::fun(1)(2);
      $this->bar = ($scope['Functions__Inner'])->fun3(5);
    }
  }
  public function fun2($v) {
    return function ($b) use ($v) {
      return ($this->scope['Functions\Inner'])->fun3($b);
    }
}

functions.purs

module Functions where

import Functions.Inner (fun3)

fun2 :: Int -> Int -> Int
fun2 _ b = b

foo :: Int
foo = fun2 1 2

bar :: Int
bar = fun3 5

Functions_Inner.php

<?php

namespace Functions;

class Inner {
    // Added a getScope static method
    public static function getScope() {
      return ['Some\Other' => 3];
    }
  
    // The constructor sets the scope
    public function __construct($scope) {
      if ($scope !== []) {
        $this->scope = $scope;
        $this->foreignVal = $scope['Some\Other'];
      }
    }

    // This from static to non-static
    public function fun3 ($arg) {
        return $arg + $this->foreignVal;
    }
}