Calculator Plugin for DMS Launcher

A launcher plugin that evaluates mathematical expressions and copies results to the clipboard.

Features

• Real-time calculation: Type mathematical expressions directly in the launcher
• Default prefix: Uses = as the default trigger prefix (configurable)
• Safe evaluation: Only allows mathematical operations, preventing code injection
• Clipboard integration: Press Enter to copy the result to clipboard
• Multiple operations: Supports +, -, *, /, ^, %, and parentheses
• Math functions: sin, cos, tan, sqrt, log, ln, pow, abs, floor, ceil, round, and more
• Constants: pi and e
• Degree trig: sind, cosd, tand for degree-based trigonometry
• Qalc engine support: Optionally use qalc (libqalculate) for unit conversions, hex, currency, and more
• Numbat engine support: Optionally use numbat for scientific computations with physical dimensions and units
• Calculation history: Recent results are shown when the trigger is typed with no expression, newest first (in-memory, configurable size)
• Persistent history: Optionally save history to a JSON file so it survives DMS restarts

Installation

Via DMS

dms plugins install Calculator

Via DMS GUI

• Mod + ,
• Go to Plugins Tab
• Choose Browse
• Enable third party
• install Calculator

Manually

cd ~/.config/DankMaterialShell/plugins
git clone https://github.com/rochacbruno/DankCalculator Calculator

1. Open DMS Settings (Ctrl+,)
2. Navigate to Plugins tab
3. Click "Scan for Plugins"
4. Enable the "Calculator" plugin with the toggle switch

Usage

With Default Settings (= Prefix)

1. Open the launcher (Ctrl+Space)
2. Type the = prefix followed by a mathematical expression: = 3 + 3
3. The result (6) appears as a launcher item
4. Press Enter to copy the result to clipboard

Customizing the Trigger

You can configure a different trigger prefix or disable it entirely in the settings:

1. Open Settings → Plugins → Calculator
2. Change the trigger to a custom value (e.g., calc, c, math)
3. Or check "No trigger (always active)" to remove the prefix requirement
4. In the launcher, type your configured trigger: calc 3 + 3 or just 3 + 3 (if no trigger)
5. Press Enter to copy the result

Using the Qalc Engine

The plugin supports an alternative calculation engine powered by qalc (libqalculate), which adds unit conversions, hex/binary conversions, currency conversion, and many more features.

To enable it:

1. Install qalc on your system (e.g., sudo dnf install qalculate or sudo apt install qalc)
2. Open Settings → Plugins → Calculator
3. Change Calculation Engine from "Default (JavaScript)" to "Qalc (libqalculate)"

Qalc examples:

Expression	Result
= 12cm to inches	4.724409449 in
= 255 to hex	0xFF
= 100 USD to EUR	(current exchange rate)
= 15% of 200	30
= sqrt(144)	12
= pi * 3^2	28.274333882...
= 5 gallons to liters	18.92705892 L

Using the Numbat Engine

The plugin also supports numbat, a statically typed language for scientific computations with first-class support for physical dimensions and units.

To enable it:

1. Install numbat on your system (e.g., cargo install numbat or via your package manager)
2. Open Settings -> Plugins -> Calculator
3. Change Calculation Engine from "Default (JavaScript)" to "Numbat"

Numbat examples:

Expression	Result
= 5 * 5	25
= 12 cm -> inches	4.72441 in
= 30 km/h -> mi/h	18.6411 mi/h
= sqrt(144)	12
= pi * 3^2	28.2743...
= 1.2e3 J -> kWh	3.33333e-4 kWh

See the numbat documentation for the full list of supported features.

Viewing History

After calculating expressions, you can recall recent results:

1. Open the launcher and type just the trigger (e.g., =)
2. Your recent calculations appear as a list, newest first
3. Select any history item to copy its result to clipboard

History is stored in-memory by default and clears when DMS restarts. The number of entries kept is configurable via the History Size setting (default: 10).

Persisting History

To keep history across DMS restarts:

1. Open Settings -> Plugins -> Calculator
2. Enable Persist History
3. Optionally set a custom History File Path (defaults to <plugins>/calculator_history.json)

When enabled, history is saved to a JSON file every time a result is copied, and loaded back on startup.

Adding a keybinding (niri)

binds {
      Mod+Shift+C hotkey-overlay-title="Calculator" {
        spawn "dms" "ipc" "call" "spotlight" "openQuery" "=";
    }
}

Supported Operations

Default Engine (JavaScript)

Arithmetic:

• Addition: = 3 + 3 → 6
• Subtraction: = 10 - 5 → 5
• Multiplication: = 4 * 7 → 28
• Division: = 20 / 4 → 5
• Exponentiation: = 2 ^ 8 → 256
• Modulo: = 17 % 5 → 2
• Parentheses: = (5 + 3) * 2 → 16
• Decimals: = 3.14 * 2 → 6.28
• Complex: = (10 + 5) * 2 - 3 / 3 → 29

Math functions:

• Trigonometric (radians): = sin(pi/2) → 1, = cos(0) → 1, = tan(pi/4) → 1
• Trigonometric (degrees): = sind(90) → 1, = cosd(60) → 0.5, = tand(45) → 1
• Inverse trig: = asin(1) → 1.5707..., = acos(0) → 1.5707..., = atan(1) → 0.7853...
• Hyperbolic: = sinh(1), = cosh(1), = tanh(0.5) and inverse variants (asinh, acosh, atanh)
• Logarithmic: = log(100) → 2 (base 10), = ln(e) → 1 (natural)
• Roots: = sqrt(144) → 12, = cbrt(27) → 3
• Rounding: = floor(3.7) → 3, = ceil(3.2) → 4, = round(3.5) → 4, = trunc(3.9) → 3
• Other: = abs(-5) → 5, = min(3, 7) → 3, = max(3, 7) → 7, = pow(2, 10) → 1024
• Constants: = pi * 2 → 6.2831..., = e ^ 2 → 7.389...
• Combined: = sqrt(pow(3, 2) + pow(4, 2)) → 5

Qalc Engine (libqalculate)

Supports everything the default engine does, plus:

• Unit conversions: = 12cm to inches, = 5 gallons to liters
• Hex/Binary: = 255 to hex, = 0xFF to decimal
• Percentages: = 15% of 200
• Currency: = 100 USD to EUR
• Functions: = sqrt(144), = sin(45 deg), = log(1000)
• Constants: = pi * r^2, = c / 2 (speed of light)

See the qalc manual for a full list of supported features.

Numbat Engine

Supports everything the default engine does, plus:

• Unit conversions: = 12 cm -> inches, = 5 gallon -> liter
• Speed/compound units: = 30 km/h -> mi/h
• Functions: = sqrt(144), = sin(45 deg), = log(1000)
• Constants: = pi * 3^2, = speed_of_light
• Date/time: = now() -> unixtime
• Scientific notation: = 1.2e3 J -> kWh

See the numbat documentation for a full list of supported features.

Examples

Expression	Result
= 3 + 3	6
= 100 / 4	25
= 2 ^ 10	1024
= (5 + 3) * 2	16
= 3.14159 * 2	6.28318
= 16 ^ 0.5	4 (square root)
= sin(pi/2)	1
= sqrt(144)	12
= log(100)	2
= sind(30)	0.5
= pi * 2	6.28318...

Security

The default JavaScript engine uses safe expression evaluation:

• Only allows numbers, operators (+, -, *, /, ^, %), parentheses, dots, and whitelisted math function names
• Math function names (sin, cos, sqrt, etc.) are validated against a strict whitelist before evaluation
• Rejects any expressions with unrecognized letters or special characters
• Prevents code injection by validating input before evaluation

The qalc engine delegates evaluation to the qalc binary, which runs as a sandboxed child process.

The numbat engine delegates evaluation to the numbat binary, which runs as a persistent interactive process.

Files

• plugin.json - Plugin manifest
• CalculatorLauncher.qml - Main launcher component
• CalculatorSettings.qml - Settings UI
• calculator.js - Safe expression evaluation logic (default engine)
• QalcService.qml - Qalc process manager singleton (qalc engine)
• NumbatService.qml - Numbat process manager singleton (numbat engine)
• qmldir - QML module directory
• README.md - This file

Configuration

Settings are stored in ~/.config/DankMaterialShell/plugin_settings.json under the calculator plugin key:

{
  "pluginSettings": {
    "calculator": {
      "trigger": "=",
      "noTrigger": false,
      "calcEngine": "default",
      "keepLastResults": "10",
      "persistHistoryOnFile": false,
      "historyFilePath": ""
    }
  }
}

Set "calcEngine" to "qalc" for the qalc engine, "numbat" for the numbat engine, or "default" for the built-in JavaScript engine.

Troubleshooting

Calculator items don't appear:

• Make sure the plugin is enabled in Settings → Plugins
• Check that you're typing a valid mathematical expression
• Try disabling "No trigger" and setting a specific trigger

Result shows wrong value:

• JavaScript has floating-point precision limitations
• Very large or very small numbers may use scientific notation
• Try switching to the qalc engine for better precision

Qalc engine shows "Calculating..." but no result:

• Make sure qalc is installed and available in your PATH
• Test by running qalc -t "2+2" in a terminal

Numbat engine shows "Calculating..." but no result:

• Make sure numbat is installed and available in your PATH
• Test by running numbat -e '2+2' in a terminal
• Check the Numbat Command setting if using a custom binary path

Copy to clipboard doesn't work:

• Make sure your system clipboard is accessible
• Check console for error messages

Author

Bruno Cesar Rocha