rustcalc

Simple REPL for mathematical expressions. Mostly a toy project to learn Rust and parsers.

Build

Rustcalc requires Rust. To build a release binary and execute it, run:

$ cargo build --release
$ ./target/release/rustcalc

Alternatively, build and run it directly with cargo run, or test it with cargo test.

Usage

Running the binary will start a REPL (read-evaluate-print-loop):

$ rustcalc
> 1 + 2 * 3.14
7.28

> 2 ^ (-1 / 2)
0.7071067811865476

> sin(pi / 4) * √2
1

> 1e100 / (1 / 0)
0

An expression can also be given as a command-line argument, e.g. rustcalc "1 + 2 * 3" will output 7 and exit. Debug output can be enabled with the --debug switch, see --help for more info.

Expressions

Rustcalc supports simple mathematical expressions with the usual operations, and has a very basic type system entirely made up of 64-bit floating-point numbers.

Numbers

Number literals can be expressed with digits and the decimal point ., as well as in scientific notation using e to signify powers of ten - for example 314, 3.14, and 3.14e2.

Numerical values are always encoded as 64-bit IEEE 754 binary64 double-precision floating point numbers. These have a magnitude of roughly 10^-307 to 10³⁰⁸, and can represent 15 significant figures with exact precision - beyond this, significant figures are rounded to 53-bit precision.

Arithmetic using integer values is exact up to 53 bits, while arithmetic using decimal values may be inexact due to their machine representation. The special values infinity (inf) and not-a-number (NaN) are fully supported, and are typically returned for invalid or undefined operations such as division by zero and numeric overflow.

Constants

The following case-insensitive constants are supported:

• pi, π: 3.141592653589793.
• e: 2.718281828459045.
• inf: the IEEE 754 infinity value.
• nan: the IEEE 754 not-a-number value.

Prefix Operators

• +: the identity operation, e.g. +2 yields 2.
• -: negation, e.g. -(1 + 2) yields -3.
• √: square root, e.g. √4 yields 2.

Postfix Operators

• !: factorial, e.g. 5! yields 120.

Infix Operators

• +: addition, e.g. 2 + 3 yields 5.
• -: subtraction, e.g. 2 - 3 yields -1.
• *: multiplication, e.g. 2 * 3 yields 6.
• /: division, e.g. 4 / 2 yields 2.
• %: modulo, e.g. 7 % 4 yields 3. Has sign of dividend and magnitude less than divisor.
• ^: exponentiation, e.g. 2 ^ 3 yields 8.

Operator Precedence

Operator precedence and associativity is listed below, and can be overridden by grouping expressions in parentheses, e.g. (1 + 2) * 3 yields 9.

Operators	Prec	Assoc
!	4	left
^	3	right
*, /, %	2	left
+, -	1	left
√	1	right

Functions

Functions are expressed as name(a, b), where arguments must be numerical values. They return a single number, or NaN on error.

• round(n, [d]): rounds n to the number of decimals given by d (default 0), e.g. round(3.14) yields 3 and round(3.14, 1) yields 3.1.
• sqrt(n): returns the square root of the given number, e.g. sqrt(4) yields 2.

Trigonometric functions

• radians(d): converts the angle d in degrees to radians e.g. radians(180) yields ~3.14.
• degrees(r): converts the angle r in radians to degrees, e.g. degrees(pi) yields 180.
• sin(r): returns the sine of the given angle in radians, e.g. sin(pi/2) yields 1.
• cos(r): returns the cosine of the given angle in radians, e.g. cos(pi) yields -1.
• tan(r): returns the tangent of the given angle in radians, e.g. tan(pi/4) yields 1.