Add: 'const' keyword to allow users to define new constants (#302)

* Add: 'const' keyword to allow users to define new constants

* Fix: delay item 'id' validation to allow use of user-defined constants

* Fix: delay disable_item 'id' validations to allow use of user-defined constants

* Codechange: Use "const" in 030_house regression test

nml/ast/constant.py

@@ -0,0 +1,47 @@
+__license__ = """
+NML is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+NML is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along
+with NML; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA."""
+
+from nml import expression, generic, global_constants
+from nml.ast import base_statement
+
+
+class Constant(base_statement.BaseStatement):
+    def __init__(self, name, value):
+        base_statement.BaseStatement.__init__(self, "constant", name.pos, False, False)
+        self.name = name
+        self.value = value
+
+    def register_names(self):
+        if not isinstance(self.name, expression.Identifier):
+            raise generic.ScriptError("Constant name should be an identifier", self.name.pos)
+        if self.name.value in global_constants.constant_numbers:
+            raise generic.ScriptError("Redefinition of constant '{}'.".format(self.name.value), self.name.pos)
+        global_constants.constant_numbers[self.name.value] = self.value.reduce_constant(
+            global_constants.const_list
+        ).value
+
+    def debug_print(self, indentation):
+        generic.print_dbg(indentation, "Constant")
+        generic.print_dbg(indentation + 2, "Name:")
+        self.name.debug_print(indentation + 4)
+
+        generic.print_dbg(indentation + 2, "Value:")
+        self.value.debug_print(indentation + 4)
+
+    def get_action_list(self):
+        return []
+
+    def __str__(self):
+        return "const {} = {};".format(self.name, self.value)

nml/ast/disable_item.py

@@ -39,18 +39,17 @@ def __init__(self, param_list, pos):
                 "disable_item() requires between 1 and 3 parameters, encountered {:d}.".format(len(param_list)), pos
             )
         self.feature = general.parse_feature(param_list[0])
+        self.first_id = param_list[1] if len(param_list) > 1 else None
+        self.last_id = param_list[2] if len(param_list) > 2 else None
 
-        if len(param_list) > 1:
-            self.first_id = param_list[1].reduce_constant(global_constants.const_list)
-        else:
-            self.first_id = None
+    def pre_process(self):
+        if self.first_id is not None:
+            self.first_id = self.first_id.reduce_constant(global_constants.const_list)
 
-        if len(param_list) > 2:
-            self.last_id = param_list[2].reduce_constant(global_constants.const_list)
+        if self.last_id is not None:
+            self.last_id = self.last_id.reduce_constant(global_constants.const_list)
             if self.last_id.value < self.first_id.value:
-                raise generic.ScriptError("Last id to disable may not be lower than the first id.", pos)
-        else:
-            self.last_id = None
+                raise generic.ScriptError("Last id to disable may not be lower than the first id.", self.last_id.pos)
 
     def debug_print(self, indentation):
         generic.print_dbg(indentation, "Disable items, feature=" + str(self.feature.value))

nml/ast/item.py

@@ -51,10 +51,7 @@ def __init__(self, params, body, pos):
         if self.feature.value in (0x08, 0x0C, 0x0E):
             raise generic.ScriptError("Defining item blocks for this feature is not allowed.", self.pos)
         self.name = params[1] if len(params) >= 2 else None
-
-        self.id = params[2].reduce_constant(global_constants.const_list) if len(params) >= 3 else None
-        if isinstance(self.id, expression.ConstantNumeric) and self.id.value == -1:
-            self.id = None  # id == -1 means default
+        self.id = params[2] if len(params) >= 3 else None
 
         if len(params) >= 4:
             if self.feature.value != 0x07:
@@ -66,6 +63,11 @@ def __init__(self, params, body, pos):
             self.size = None
 
     def register_names(self):
+        if self.id is not None:
+            self.id = self.id.reduce_constant(global_constants.const_list)
+            if isinstance(self.id, expression.ConstantNumeric) and self.id.value == -1:
+                self.id = None  # id == -1 means default
+
         if self.name:
             if not isinstance(self.name, expression.Identifier):
                 raise generic.ScriptError("Item parameter 2 'name' should be an identifier", self.pos)

nml/parser.py

@@ -24,6 +24,7 @@
     basecost,
     cargotable,
     conditional,
+    constant,
     deactivate,
     disable_item,
     error,
@@ -153,7 +154,8 @@ def p_main_block(self, t):
         | snowline
         | engine_override
         | sort_vehicles
-        | basecost"""
+        | basecost
+        | constant"""
         t[0] = t[1]
 
     #
@@ -839,3 +841,7 @@ def p_tilelayout_item_tile(self, t):
     def p_tilelayout_item_prop(self, t):
         "tilelayout_item : assignment"
         t[0] = t[1]
+
+    def p_constant(self, t):
+        "constant : CONST expression EQ expression SEMICOLON"
+        t[0] = constant.Constant(t[2], t[4])

nml/tokens.py

@@ -61,6 +61,7 @@
     "recolour_sprite":     "RECOLOUR_SPRITE",
     "engine_override":     "ENGINE_OVERRIDE",
     "sort":                "SORT_VEHICLES",
+    "const":               "CONST"
 }
 # fmt: on
 

regression/030_house.nml

@@ -50,8 +50,8 @@ spriteset(brewery_spriteset_building) {
     tmpl_building_sprite(150, 60, 91, -60, "brewery_snow.png")
 }
 
-default_palette = PALETTE_USE_DEFAULT;
-/* Generic sprite layout that is used for all tiles of the building. Parmaeters:
+const default_palette = PALETTE_USE_DEFAULT;
+/* Generic sprite layout that is used for all tiles of the building. Parameters:
  * - building_sprite: offset in the brewery_spriteset_building spriteset to use. -1 to skip building sprite.
  * - with_smoke: Show smoke above the tile (also depends on animation state) */
 spritelayout brewery_sprite_layout(building_sprite, with_smoke) {