# README

mathcat

mathcat is an expression evaluating library and REPL in Go with basic arithmetic, functions, variables and more.

Features

mathcat doesn't just evaluate basic expressions, it has some tricks up its sleeve. Here's a list with some of its features:

Hex literals (0xDEADBEEF)
Binary literals (0b1101001)
Octal literals (0o126632)
Scientific notation (24e3)
Variables (with UTF-8 support)
Functions (list)
Bitwise operators
Relational operators
Some handy predefined variables
Its own REPL

Installation

Library

go get github.com/soudy/mathcat

REPL

go get github.com/soudy/mathcat/cmd/mc

REPL usage

The REPL can be used by simply launching mc:

mc> 8**8
16777216
mc> (8**8) - e # Look, a comment!
16777213.281718171541

Or it can read from stdin like so:

$ echo "3**pi * (6 - -7)" | mc

Arguments

Name	Description	Default
precision	bits of decimal precision used in decimal float results	64
mode	type of literal used as result. can be decimal, hex, binary or octal	decimal

Library usage

There are three different ways to evaluate expressions, the first way is by calling Eval, the second way is by creating a new instance and using Run, and the final way is to use Exec in which you can pass a map with variables to use in the expression.

Eval

If you're not planning on declaring variables, you can use Eval. Eval will evaluate an expression and return its result.

res, err := mathcat.Eval("2 * pi * 5") // pi is a predefined variable
if err != nil {
    // handle errors
}
fmt.Printf("Result: %s\n", res.FloatString(6)) // Result: 31.415927

Run

You can use Run for a more featureful approach. With this method you can assign and use variables across the Parser instance.

p := mathcat.New()
p.Run("a = 1")
p.Run("b = 3")
res, err := p.Run("a + b * b") // 10

Exec

To pass external variables to an expression without using Run, you can use Exec to pass a map of variables.

res, err := mathcat.Exec("a + b * b", map[string]*big.Rat{
    "a": big.NewRat(1, 1),
    "b": big.NewRat(3, 1),
}) // 10

Besides evaluating expressions, mathcat also offers some other handy functions.

GetVar

You can get a defined variable at any time with GetVar.

p := mathcat.New()
p.Run("酷 = -33")
if val, err := p.GetVar("酷"); !err {
    fmt.Printf("%f\n", val) // -33
}

IsValidIdent

Check if a string qualifies as a valid identifier

mathcat.IsValidIdent("a2") // true
mathcat.IsValidIdent("6a") // false

RationalToInteger

Convert a big.Rat to a big.Int. Useful for printing in other bases or when you're only working with integers.

integer := mathcat.RationalToInteger(big.NewRat(42, 1))
fmt.Printf("%#x\n", integer) // prints 0x2a

Supported operators

Operator	Description
=	assignment
+	addition
-	subtraction
/	division
*	multiply
**	power
%	remainder
&	bitwise and
\|	bitwise or
^	bitwise xor
<<	bitwise left shift
>>	bitwise right shift
~	bitwise not
==	equal
!=	not equal
>	greater than
>=	greater than or equal
<	less than
<=	less than or equal

All of these except ~ and relational operators also have an assignment variant (+=, -=, **= etc.) that can be used to assign values to variables.

Functions

mathcat has a big list of functions you can use. A function call is invoked like in most programming languages, with an identifier followed by a left parentheses like this: max(5, 10).

Function	Arguments	Description
abs(n)	1	returns the absolute value of given number
sin(n)	1	returns the sine of given number
cos(n)	1	returns the cosine of given number
tan(n)	1	returns the tangent of given number
asin(n)	1	returns the arcsine of given number
acos(n)	1	returns the acosine of given number
atan(n)	1	returns the arctangent of given number
ceil(n)	1	returns the smallest integer greater than or equal to a given number
floor(n)	1	returns the largest integer less than or equal to a given number
ln(n)	1	returns the natural logarithm of given number
log(n)	1	returns the the decimal logarithm of given number
logn(k, n)	2	returns the the k logarithm of n
max(a, b)	2	returns the larger of the two given numbers
min(a, b)	2	returns the smaller of the two given numbers
sqrt(n)	1	returns the square root of given number
rand()	0	returns a random float between 0.0 and 1.0
fact(n)	1	returns the factorial of given number
list()	0	list all functions