# Peano

**Peano** is an esolang invented by User:None1, inspired by Peano arithmetic.

## Arithmetic Operators

Peano has only two built-in arithmetic operators: successor and precursor, unlike Peano arithmetic which has only one.

The precursor of a is represented by `'a`

, the successor of a is represented by `a'`

.

Precursor and successor operators cancel out each other, for example `'a'`

returns `a`

and *a'** returns 'a.*

## Numbers

The number system in Peano is positive integers (0 not included!), it is invalid to access the precursor of 1.

## Comparison operators

Peano has only one comparison operator: `~`

which checks if the value is 1, returns 1 if it is and 2 (1') if it isn't.

Brackets are allowed to prioritize operators.

## Functions

Functions are like this:

!func(p1,p2,...)con1:exp1con2:exp2con3:exp3...expn;

If con1 is 1, return exp1, otherwise if con2 is 1, return exp2, ..., return expn.

## I/O

Peano uses non-interactive input, it can only input number sequences. The inputs is stored in the variables *i1*,*i2*,...

Output can only be done in the global scope implicitly.

expr

prints the value of *expr*. Output format is implementation defined (e.g.: You can print 1'** or 5 for the number five).**

## Examples

### Add function

!add(a,b) ~a:b' add('a,b)' ;

### A+B Problem

!add(a,b) ~a:b' add('a,b)' ; add(i1,i2)