Use nix eval --expr instead of nix-instantiate --eval --expr:
$ nix-instantiate --eval --expr '(x: y: { a = x + "-" + y; }) "a" "b"'
{ a = <CODE>; }
$ nix eval --expr '(x: y: { a = x + "-" + y; }) "a" "b"'
{ a = "a-b"; }For node you must use console.log unless it is already in the example.
$ node -e 'console.log(((x, y) => ({ a: x + "-" + y }))("a", "b"))'
{ a: 'a-b' }If you want to have nix eval available in nixos stable, you need to install unstable nix command as described in https://nixos.wiki/wiki/Flakes.
| Nix | Javascript |
|---|---|
"Hello world!" |
"Hello world!" |
2/3 |
require("path").join("2", "3") |
2/ 3 |
Math.ceil(2/3) |
2/ 3. |
2/3 |
(a: { a = a; }) 2 |
(a => ({ a: a }))(2) |
(a: { inherit a; }) 2 |
(a => ({ a }))(2) |
(a: b: { a = a; b = b; }) 2 3 |
((a, b) => ({ a: a, b: b }))(2, 3) |
((a: b: { inherit a b; }) 2) 3 |
(a => b => ({ a, b }))(2)(3) |
({ a }: { inherit a; }) { a = 2; } |
(({ a }) => ({ a }))({ a: 2 }) |
({ a, b, ... }: { inherit a b; }) { a = 2; b = 3; c = 4; } |
(({ a, b }) => ({ a, b }))({ a: 2, b: 3, c: 4 }) |
(a: { c = a.b.c; }) { b = { c = 2; }; } |
(a => ({ c: a.b.c }))({ b: { c: 2 } }) |
(a: { inherit (a.b) c; }) { b = { c = 2; }; } |
(a => ({ c: a.b.c }))({ b: { c: 2 } }) |
({ a ? 2 }: a) {} |
(({ a = 2 }) => a)({}) |
let double = x: x*2; in double 3 |
const double = x => x*2; console.log(double(3)); |
let mul = a: (b: a*b); in (mul 2) 3 |
const mul = a => b => a*b; console.log(mul(2)(3)); |
let x = 3; mul = a: (b: a*b); in (mul 2) 3 |
const x = 3, mul = a => b => a*b; console.log(mul(x)(3)); |
if true then 3 else 2 |
true ? 3: 2 |
- https://learnxinyminutes.com/docs/nix/
- https://medium.com/@MrJamesFisher/nix-by-example-a0063a1a4c55
- https://nixery.dev/nix-1p.html
- https://nixos.org/manual/nix/unstable/command-ref/new-cli/nix3-eval.html
- https://nixos.wiki/wiki/Nix_command/eval
- https://nixos.org/guides/nix-pills/functions-and-imports.html
You can read that Nix is Nix expression language.
Expression: Something which evaluates to a value. Example: 1+2/x
Statement: A line of code which does something. Example: GOTO 100
Or another explanation:
Expression -- from the New Oxford American Dictionary:
expression: Mathematics a collection of symbols that jointly express a quantity : the expression for the circumference of a circle is 2πr.
Statement from Wikipedia:
In computer programming a statement can be thought of as the smallest standalone element of an imperative programming language. A program is formed by a sequence of one or more statements. A statement will have internal components (e.g., expressions).
- https://stackoverflow.com/questions/19132/expression-versus-statement/19224#19224
- https://stackoverflow.com/questions/4728073/what-is-the-difference-between-an-expression-and-a-statement-in-python/4730559#4730559
Below const a is a statement which consist of expression. Conditional (ternary) operator is an expression.
const a = true ? 1 : 0;Description from Nickel, possible successor of Nix language:
Its purpose is to automate the generation of static configuration files - think JSON, YAML, XML, or your favorite data representation language - that are then fed to another system. It is designed to have a simple, well-understood core: it is in essence JSON with functions.