calc

README

calc

calc is a REPL for arithmetic. It reads Go expressions and computes them with exact arithmetic.

Install:

go install github.com/croaky/calc@latest

Start the REPL:

$ calc
> 2 + 2
4
> (12 + 4) * 3 / 2.5
19.2
> 7 / 2
3.5
> 0.1 + 0.2
0.3
> _ * 10
3
> 1 << 70
1180591620717411303424
> quit

Give an expression as arguments to print one result and exit:

calc '7 / 2'

Pipe expressions on stdin, one per line, to print one result per line:

printf '2 + 2\n_ * 10\n' | calc

Expressions

An expression is a Go constant expression: integer and floating-point literals (1_000, 0xff, 1e-3), parentheses, and the operators + - * / % & | ^ &^ << >>. %, the bitwise operators, and the shifts need integers.

/ gives the exact quotient. 7 / 2 is 3.5, not Go's truncated 3.

calc holds each value as an exact integer or rational, as the Go compiler holds a constant. So 0.1 + 0.2 is 0.3, and an integer keeps every digit. calc rounds to a float64 only to print a fraction.

_ is the result of the last line that gave one, as in irb.

Keys

• Up and Down: walk the history.
• Ctrl+A and Ctrl+E: move to the start and the end of the line.
• Ctrl+R: search the history.
• Ctrl+C: discard the line.
• Ctrl+D on an empty line, exit, or quit: exit.

calc saves the history in ~/.calc_history, so the up arrow reaches lines from an earlier session.

calc depends on peterh/liner for line editing.

Developing

Checkfile lists the checks CI runs. AGENTS.md gives the commands to run before a commit, and the commit message rules.

GitHub repo is a mirror

Development happens on sockeye, a self-hosted review and CI server, which holds in-progress branches. GitHub receives main so go install works.

License

MIT

Documentation

Overview

calc is a REPL for arithmetic. It reads Go expressions, computes them with exact arithmetic, and prints the result.

calc            # start the REPL
calc '7 / 2'    # print one result and exit
echo 2+2 | calc # read one expression per line from stdin