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Merge pull request #388 from fricklerhandwerk/nix-language-introduction
rework parentheses example
This commit is contained in:
Valentin Gagarin
GitHub
commit
6ae488e715
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@ -43,8 +43,9 @@ This tutorial only covers the most important language features, briefly discusse
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### What will you learn?
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This tutorial should enable you to read typical Nix language code and understand its structure.
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Its goal is to highlight where the Nix language may differ from languages you are used to.
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It shows the most common and distingushing patterns in the Nix language:
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It therefore shows the most common and distingushing patterns in the Nix language:
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- [Assigning names and accessing values](names-values)
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- Declaring and calling [functions](functions)
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@ -53,7 +54,8 @@ It shows the most common and distingushing patterns in the Nix language:
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- [Derivations](derivations) that describe build tasks
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:::{important}
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This tutorial *does not* explain all Nix language features in detail.
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This tutorial *does not* explain all Nix language features in detail and *does not* go into specifics of syntactical rules.
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See the [Nix manual][manual-language] for a full language reference.
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:::
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@ -223,61 +225,31 @@ reading files, to capture what build tasks will operate on.
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There is nothing else to it.
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What may look complicated comes not from the language, but from how it is used.
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### Notes on syntax
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### Notes on whitespace
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This tutorial does not go into the specifics of syntactical rules, but rather puts emphasis on recurrent patterns as observed in practical code and what they mean.
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The most important heuristics to avoid confusion are about white space and parentheses, since in that regard, the Nix language may differ from languages you are used to.
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(Don't worry if you don't understand the examples here, they are only for illustration.)
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1. White space is used to delimit [lexical tokens], where required.
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It is otherwise insignificant.
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Line breaks, indentation, and additional spaces are for readers' convenience.
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The following are equivalent:
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```nix
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let
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x = 1;
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y = 2;
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in x + y
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```
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3
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```nix
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let x=1;y=2;in x+y
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```
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3
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White space is used to delimit [lexical tokens], where required.
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It is otherwise insignificant.
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[lexical tokens]: https://en.m.wikipedia.org/wiki/Lexical_analysis#Token
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2. Parentheses are used to force precedence.[^inherit-parens]
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Line breaks, indentation, and additional spaces are for readers' convenience.
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The following are different:
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The following are equivalent:
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```nix
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let
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f = x: x + 1;
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a = 1;
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in [ (f a) ]
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```
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```nix
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let
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x = 1;
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y = 2;
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in x + y
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```
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[ 2 ]
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3
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```nix
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let
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f = x: x + 1;
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a = 1;
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in [ f a ]
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```
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```nix
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let x=1;y=2;in x+y
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```
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[ <LAMBDA> 1 ]
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[^inherit-parens]: [`inherit`](inherit) is the only exception where parentheses are a syntactical requirement.
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3
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(names-values)=
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## Names and values
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@ -1048,16 +1020,13 @@ Calling a function with an argument means writing the argument after the functio
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Example:
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```nix
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(x: x + 1) 1
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let
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f = x: x + 1;
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in f 1
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```
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2
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:::{note}
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Function and argument are separated by white space.
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Therefore, in this case parantheses (`( )`) are required to distinguish the function declaration and its argument.
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:::
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Example:
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```nix
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@ -1084,6 +1053,51 @@ f v
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1
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Since function and argument are separated by white space, sometimes parentheses (`( )`) are required to achieve the desired result.
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Example:
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```nix
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(x: x + 1) 1
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```
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2
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<details><summary>Detailed explanation</summary>
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This expression applies an anonymous function `x: x + 1` to the argument `1`.
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The function has to be written in parentheses to distinguish it from the argument.
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</details>
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Example:
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List elements are also separated by white space, therefore the following are different:
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```nix
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let
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f = x: x + 1;
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a = 1;
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in [ (f a) ]
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```
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[ 2 ]
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```nix
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let
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f = x: x + 1;
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a = 1;
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in [ f a ]
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```
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[ <LAMBDA> 1 ]
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The first example reads: apply `f` to `a`, and put the result in a list.
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The resulting list has one element.
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The second example reads: put `f` and `a` in a list.
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The resulting list has two elements.
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#### Multiple arguments
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Also known as “[curried] functions”.
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