Simple calculator

Parse and calculate numbers from strings like 2 * (12.4 / (7 + -2)), or multi-line inputs that separated by semicolons like x = 2; y = 5.25; z = x * (3 + -y); z.

Based on Pratt parsing and jdvillal/parser.

Supported operators:

• +
• -
• *
• /
• **
• ( and )

Supported expressions like:

• -.25 + 2
• -1 + -2 * -3
• -5 * (2 + -.3)
• 2 * (12.4 / (7 + -2))
• -34 * (2 + -.23)
• 4 * (272 + 6) - 324 / 8
• 2 ** 10
• x = 2; y = 5.25; z = x * (3 + -y); z
• x = 1.6; y = .25; -((2.5 * x) ** 6) ** y / .5 ** 3

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How it works

The calculator processes an input in three stages:

1. Lex: splits the input string into tokens.
2. Parse: builds an Expression AST (Abstract Syntax Tree) from tokens with binding power of each operator.
3. Evaluate: traverses the AST to compute the final result.

Example

0. Input

   -16 ** (.25 + (7 - -2) / 4)

1. Input -> Lex -> Tokens

   ["-", "16", "**", "(", ".25", "+", "(", "7", "-", "-", "2", ")", "/", "4", ")"]

2. Tokens -> Parse -> Expression (binding powers: ** > - negative sign, / > + and -)

   (- 0 (** 16 (+ 0.25 (/ (- 7 (- 0 2)) 4))))

3. Evaluate -> result

   -1024

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Run the calculator

Download the golang.org/x/term package

go mod tidy

Test

go test -v ./...

Run

go run .

Run with debug mode to observe each stage of processing

DEBUG=1 go run .

Usage

After starting the calculator, you can type expressions directly into the interactive terminal, assign variables, or use built-in commands.

For example:

Enter an expression (or 'exit' to quit):
>>> 2 * (12.4 / (7 + -2))
4.96
>>> x = 10
>>> x * 3
30

Input help to see a list of available commands, supported operators, and syntax information.