[Formula Language] $($var1 - 1 + $var2) does not evaluate

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Bobit
Posts: 33
Joined: February 10th, 2015, 2:42 pm

[Formula Language] $($var1 - 1 + $var2) does not evaluate

Post by Bobit »

(it's possible this is just user error and either the - or + operator is overloaded, but if so it's still confusing)

$($var1 - 1 + $var2) does not evaluate, even when $($var1 - 1 - -$var2) does evalulate.

Reproduction steps:

Simply put this in your scenario.cfg and run the scenario

Code: Select all

    [event]
        name = prestart
        id = test
        [store_map_dimensions]
        [/store_map_dimensions]
        [message]
            message = $($map_size[0].height - 1 + $map_size[0].height)
        [/message]
        [message]
            message = $($map_size[0].height - 1 - -$map_size[0].height)
        [/message]
    [/event]
The first message will be blank, the second will not


OS: Windows 11
Build info:
The Battle for Wesnoth version 1.16.1 x86_64
Running on Microsoft Windows 11 21H2 (10.0.22000) x86_64
Distribution channel: Steam

Game paths
==========

Data dir: C:\Program Files (x86)\Steam\steamapps\common\wesnoth
User config dir: C:\Users\USER\OneDrive\Documents\My Games\Wesnoth1.16
User data dir: C:\Users\USER\OneDrive\Documents\My Games\Wesnoth1.16
Saves dir: C:\Users\USER\OneDrive\Documents\My Games\Wesnoth1.16\saves
Add-ons dir: C:\Users\USER\OneDrive\Documents\My Games\Wesnoth1.16\data\add-ons
Cache dir: C:\Users\USER\OneDrive\Documents\My Games\Wesnoth1.16\cache

Libraries
=========

Boost: 1.74
Lua: 5.4.2
OpenSSL/libcrypto: 1.1.1i (runtime 1.1.1i)
Cairo: 1.17.4 (runtime 1.17.4)
Pango: 1.48.0 (runtime 1.48.0)
SDL: 2.0.12 (runtime 2.0.12)
SDL_image: 2.0.5 (runtime 2.0.5)
SDL_mixer: 2.0.4 (runtime 2.0.4)

Features
========

Lua console completion: yes
Win32 notifications back end: yes

Current video settings
======================

SDL video drivers: [windows] dummy
Window size: 1707x1067
Screen refresh rate: 165
Screen dots per inch: 96.000000x96.000000
Screen dpi scale factor: 1.000000x1.000000

Current audio settings
======================

SDL audio drivers: [wasapi] directsound
Number of channels: 2
Output rate: 44100 Hz
Sample format: signed 16 bit little-endian
Sample size: 4096 bytes

Installed add-ons
=================

1The_Great_Steppe_Era: 1.2.3c
1The_Great_Steppe_Music: 0.1.4
A_Random_RPG_Adventure: 1.16.220110e
Advance_Wesnoth_Wars: 1.14.15.3
BloodLust: 0.6.3
Dungeons_of_Wesnoth: 0.61.0 Beta
Era_of_Magic: 3.5.2a
Era_of_Magic_Resources: 1.2.3
Inky_Quest: 1.6.0
Legend_of_the_Invincibles: 3.2.7b
PSR_Wesmoba: 1.16.211027
TOPGUN_Addon: 0.1.16
To_Lands_Unknown: 3.5.4
To_Lands_Unknown_Resources_1: 1.7.0
To_Lands_Unknown_Resources_2: 1.6.0
Unto_Others: 1.0.1
WML_Guide: 1.0.0
desertwar_addon: 0.2.2
vghetto
Posts: 752
Joined: November 2nd, 2019, 5:12 pm

Re: [Formula Language] $($var1 - 1 + $var2) does not evaluate

Post by vghetto »

Bobit wrote: January 13th, 2022, 6:44 am message = $($map_size[0].height - 1 + $map_size[0].height)
I've seen this before, unfortunately I can't remember where. They had to do - - to get around it as well.
Putting quotes around the expression seems to fix it though.
message = "$($map_size[0].height - 1 + $map_size[0].height)"
Without the quotes this error is produced.

Code: Select all

error engine: Formula in WML string cannot be evaluated due to Could not parse expression
gnombat
Posts: 416
Joined: June 10th, 2010, 8:49 pm

Re: [Formula Language] $($var1 - 1 + $var2) does not evaluate

Post by gnombat »

Bobit wrote: January 13th, 2022, 6:44 am (it's possible this is just user error and either the - or + operator is overloaded, but if so it's still confusing)
I think the problem is that the + operator is used in WML for string concatenation.
vghetto wrote: January 13th, 2022, 8:17 am Putting quotes around the expression seems to fix it though.
I think this is working as documented in the Wiki:
https://wiki.wesnoth.org/SyntaxWML#Special_Attribute_Values wrote: ...string concatenation is performed with the plus sign (+). If a plus sign appears outside quotes in a value, it means that the string/value on its right will be appended to the string/value on its left. To have an actual plus sign in a value, the string containing the + character must be surrounded by quotes...
Bobit
Posts: 33
Joined: February 10th, 2015, 2:42 pm

Re: [Formula Language] $($var1 - 1 + $var2) does not evaluate

Post by Bobit »

So + is always string + and not mathematical + unless it's inside quotes? In most languages with operator overloading, which method is performed depends on what types of parameters are given, not having quotes around it. Or is $map_size[0].height actually a string, not a number?
User avatar
Ravana
Forum Moderator
Posts: 2552
Joined: January 29th, 2012, 12:49 am
Location: Estonia
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Re: [Formula Language] $($var1 - 1 + $var2) does not evaluate

Post by Ravana »

If you come from common programming language background then consider using Lua instead of formulas.
gnombat
Posts: 416
Joined: June 10th, 2010, 8:49 pm

Re: [Formula Language] $($var1 - 1 + $var2) does not evaluate

Post by gnombat »

Bobit wrote: January 13th, 2022, 6:38 pm So + is always string + and not mathematical + unless it's inside quotes? In most languages with operator overloading, which method is performed depends on what types of parameters are given, not having quotes around it. Or is $map_size[0].height actually a string, not a number?
WML is not really like most programming languages, it is closer to a markup language like XML or HTML. To the WML parser, every attribute value is just a string. The WML parser may perform string concatenation (with the + operator) and/or translation (with the _ operator) but it doesn't know anything about formulas - formula evaluation will take place later, after the WML parsing stage.
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