hedgehog-finance/hedgehog-skills/math-calc

Math Calculator

Portable CLI parameters

When a documented CLI accepts a parameter object, use the same rule on every Agent and operating system; existing positional file inputs remain positional:

1. When every business value is a non-empty, single-line string | finite number | boolean, pass it as a named argument (--key value or --key=value). Names are case-sensitive and are not normalized.
2. When any value is an object, array, null, multiline text, a numeric/boolean-looking string that must remain a string, or contains difficult quoting, write the complete parameter object as UTF-8 JSON and pass the file option documented by this Skill.
3. Agent-created parameter files must have a unique basename matching tmp-<skill-name>-<unique-id>.json, must not use the reserved .hedgehog/ directory, and must be removed after the call when no longer needed. UTF-8 BOM is accepted.
4. Do not inline nested JSON or combine flat arguments with a JSON/file payload. Create JSON with the Agent's file-writing capability, not echo, a shell heredoc, or PowerShell string assembly.

POSIX/Git Bash form: node '<script>' --key 'single-line value' or node '<script>' <file-option> '<workspace>/tmp-<skill-name>-<id>.json'.

PowerShell form: node "<script>" --key "single-line value" or node "<script>" <file-option> "<workspace>\\tmp-<skill-name>-<id>.json".

On Windows, use PowerShell or a verified Git for Windows Bash; cmd.exe is unsupported. Keep each command on one physical line. The process runs with the current Agent user's permissions and that Agent's native sandbox; HogAgent marks its Windows shell as UNSANDBOXED.

A safe mathematical expression evaluator built on the expr-eval parser. Supports arithmetic operations, trigonometric functions, logarithms, factorials, conditional expressions, and more.

Runtime

• Node.js: >=18

Dependencies

Install the packages declared in this Skill's package.json before first use:

npm install --prefix "<skill_path>"

Replace <skill_path> with the directory containing this SKILL.md. Run the command again if node_modules is absent, after reinstalling/updating the Skill, or when Node reports Cannot find package / Cannot find module.

Usage

node <skill_path>/cli.mjs "<expression>" [--precision N]

Where <skill_path> is the actual installed path of this skill.

Parameters

Supported Operations

Basic Operations

• Addition, subtraction, multiplication, division: +, -, *, /
• Exponentiation: ^ or **
• Modulo: %
• Parentheses: ()

Trigonometric Functions

• sin(x), cos(x), tan(x)
• asin(x), acos(x), atan(x)

Logarithmic Functions

⚠️ Note: log(x) is the natural logarithm (base e), NOT the common logarithm!

For base-10 logarithm, use log10(x).

Other Functions

• sqrt(x): Square root
• cbrt(x): Cube root
• abs(x): Absolute value
• ceil(x), floor(x), round(x): Rounding
• trunc(x): Truncate decimals
• exp(x): e raised to the power of x
• hypot(x, y): Square root of sum of squares
• sign(x): Sign function
• fact(x) or x!: Factorial

Constants

• pi or PI: Pi (3.14159...)
• e or E: Euler's number (2.71828...)

Conditional Expressions

• x > y ? x : y: Ternary operator
• Comparison: <, >, <=, >=, ==, !=
• Logic: and, or, not

Examples

# Basic arithmetic
node <skill_path>/cli.mjs "2 + 3 * 4"
# Output: 14
 
# Trigonometric function
node <skill_path>/cli.mjs "sin(pi / 2)"
# Output: 1
 
# Logarithm
node <skill_path>/cli.mjs "log10(1000)"
# Output: 3
 
# Logarithm (note: log is natural logarithm)
node <skill_path>/cli.mjs "log(e)"
# Output: 1
node <skill_path>/cli.mjs "log10(100)"
# Output: 2
 
# Factorial
node <skill_path>/cli.mjs "fact(5)"
# Output: 120
 
# Compound expression
node <skill_path>/cli.mjs "sqrt(3^2 + 4^2)"
# Output: 5
 
# Specify precision
node <skill_path>/cli.mjs "pi" --precision 15
# Output: 3.141592653589793
 
# Conditional expression
node <skill_path>/cli.mjs "5 > 3 ? 100 : 200"
# Output: 100

Constraints

• Returns an error message when the expression is empty or invalid.
• Returns an error when the result is non-finite (overflow or invalid operation).
• Variable assignment or custom variables are not supported (only built-in constants pi and e).
• Help mode is exclusive; the CLI performs no network or subprocess calls and rejects extra options or positional values.