Make the RNG node behave more like a regular node

Prettier follow up to !190 (merged)

pystencils/rng.py

@@ -19,7 +19,7 @@ def _get_rng_template(name, data_type, num_vars):
     return template
 
 
-def _get_rng_code(template, dialect, vector_instruction_set, args, dim, result_symbols):
+def _get_rng_code(template, dialect, vector_instruction_set, args, result_symbols):
     if dialect == 'cuda' or (dialect == 'c' and vector_instruction_set is None):
         return template.format(parameters=', '.join(str(a) for a in args),
                                result_symbols=result_symbols)
@@ -44,14 +44,14 @@ class RNGBase(CustomCodeNode):
         if dim < 3:
             coordinates.append(0)
 
+        self._args = sp.sympify([time_step, *coordinates, *keys])
         self.result_symbols = tuple(TypedSymbol(f'random_{self.id}_{i}', self._data_type)
                                     for i in range(self._num_vars))
-        symbols_read = set.union(*[sp.sympify(s).atoms(sp.Symbol) for s in list(keys) + coordinates + [time_step]])
+        symbols_read = set.union(*[s.atoms(sp.Symbol) for s in self.args])
         super().__init__("", symbols_read=symbols_read, symbols_defined=self.result_symbols)
 
         self.headers = [f'"{self._name}_rand.h"']
-        self._args = sp.sympify([time_step, *coordinates, *keys])
-        self._dim = dim
+
         RNGBase.id += 1
 
     @property
@@ -60,8 +60,7 @@ class RNGBase(CustomCodeNode):
 
     def get_code(self, dialect, vector_instruction_set):
         template = _get_rng_template(self._name, self._data_type, self._num_vars)
-        return _get_rng_code(template, dialect, vector_instruction_set,
-                             self.args, self._dim, self.result_symbols)
+        return _get_rng_code(template, dialect, vector_instruction_set, self.args, self.result_symbols)
 
     def __repr__(self):
         return (", ".join(['{}'] * self._num_vars) + " \\leftarrow {}RNG").format(*self.result_symbols,