# 关于设计一门新编程语言的一点想法

I'm just putting together some random thoughts that I wish to turn into a new programming language. These are notations I often use in comments for C++ algorithms. A lot of the syntax may have been realized by mathematical languages like Mathematica or Python.

## Data types

This is a language mainly used for algorithms and maths. The data types are:

**Number**`-1.6`

,`1/3`

;**Boolean**`true`

;**String**`"Hello"`

;**Set**`{1, 2, 3}`

(no duplicate value; no order);**Matrix**`((1, 2, 3), (4, 5, 6))`

(supports matrix operations; vectors are special names for n×1 or 1×n matrices);**Function**.

## Arithmetic

Apart from the typical integer and decimal types, number types also include **fractions**, **irrational numbers**, and **complex numbers**. The special number `infty`

is used for sequence and function limits, as well as the result of division by zero.

Since fractions preserve more precision than decimals, whenever a fraction is involved in an expression, the result will be a fraction. Integers are special fractions with denominator of 1.

`num a := 1.6;`

num b := 1/3;

num c := a * b; // c = 8/15

num d := 1.6 / 3; // d = 8/15

Some operations are:

- Addition:
`+`

; - Subtraction:
`-`

; - Multiplication:
`*`

; - Division:
`/`

; - Exponentiation:
`^`

; - Assignment:
`:=`

; - Equality:
`=`

,`==`

; - Inequality:
`>`

,`<`

,`>=`

,`<=`

,`!=`

.

Any function with two parameters can be used as a binary operator.

`squaresum := (num a, num b) => a^2 + b^2;`

num c := 1 squaresum 2; // c = 5

A number literal followed by a variable is infered to be a multiplication.

`num x := 2;`

num a := 3x^2 + 2x + 1; // a = 17

## Declaring sequences

`seq a := i => i^2; // a = 0, 1, 4, 9, 16, ...`

**Sequences are functions.** More specifically, a sequence is defined as

`type seq := (num) => T;`

where the only parameter is the subscript. Unlike vectors, sequences contain an infinite number of items. `a_i`

is just a syntax sugar to `a(i)`

as in a function. For collections of finite number of objects, use vectors.

## Iterating sequences

The syntax `i...j`

returns an iterator from `i`

to `j`

, inclusive. This is akin to `range(i, j)`

in Python.

When an iterator is used in the index, it also returns an iterator.

`seq a := i => i;`

for (k in a_(1...3)) {

print(k); // Out: 1 2 3

}

## Matrix operations

Any typical matrix operation is supported. Moreover mathematical functions treat square matrices the same as numbers.

`mat a := ((1, 2, 3), (4, 5, 6), (7, 8, 9));`

mat b := cos(a);

/**

b = (( 0.38017732968947, −0.3738301457419 , −0.12783762117329),

(−0.53120649276402, 0.39010533372492, −0.68858283978612),

(−0.44259031521749, −0.84595918680825, −0.24932805839901))

*/

## Expressions

Expressions are syntax sugars for functions.

`type expr := (...T) => T;`

This is to reduce the cumbersome typing. A type like `(num, vec) => num`

can now be simply `expr`

. However, I'm not sure how robustness / type safety can be achieved in this case.

## Mathematical functions

In mathematics, parameters used in functions often appear like currying to me. For example, $\sum_{k=0}^{10}k^2$ is just a function $\sum_{k=0}^{10}$ applied to an expression $k^2$.

I propose the angle brackets be used to pass parameters to functions that return a function, while round brackets are for functions that return a value.

`sum := <num i, num j> => {`

return (expr f) => {

num s := 0;

for (x in i...j) {

s += f(x);

}

return s;

}

}

num a = sum<1, 10>(x => x^2); // a = 385

## Immutability

Although appearing to be a functional programming language, everything is by default mutable. Immutable objects have `const`

modifiers.