Merge pull request #8317 from fricklerhandwerk/doc-identifier

document identifier syntax for attribute sets

doc/manual/src/language/constructs.md

@@ -2,8 +2,11 @@
 
 ## Recursive sets
 
-Recursive sets are just normal sets, but the attributes can refer to
+Recursive sets are like normal [attribute sets](./values.md#attribute-set), but the attributes can refer to each other.
-each other. For example,
+
+> *rec-attrset* = `rec {` [ *name* `=` *expr* `;` `]`... `}`
+
+Example:
 
 ```nix
 rec {
@@ -12,7 +15,9 @@ rec {
 }.x
 ```
 
-evaluates to `123`. Note that without `rec` the binding `x = y;` would
+This evaluates to `123`.
+
+Note that without `rec` the binding `x = y;` would
 refer to the variable `y` in the surrounding scope, if one exists, and
 would be invalid if no such variable exists. That is, in a normal
 (non-recursive) set, attributes are not added to the lexical scope; in a
@@ -33,7 +38,10 @@ will crash with an `infinite recursion encountered` error message.
 ## Let-expressions
 
 A let-expression allows you to define local variables for an expression.
-For instance,
+
+> *let-in* = `let` [ *identifier* = *expr* ]... `in` *expr*
+
+Example:
 
 ```nix
 let
@@ -42,18 +50,19 @@ let
 in x + y
 ```
 
-evaluates to `"foobar"`.
+This evaluates to `"foobar"`.
 
 ## Inheriting attributes
 
-When defining a set or in a let-expression it is often convenient to
+When defining an [attribute set](./values.md#attribute-set) or in a [let-expression](#let-expressions) it is often convenient to copy variables from the surrounding lexical scope (e.g., when you want to propagate attributes).
-copy variables from the surrounding lexical scope (e.g., when you want
+This can be shortened using the `inherit` keyword.
-to propagate attributes). This can be shortened using the `inherit`
+
-keyword. For instance,
+Example:
 
 ```nix
 let x = 123; in
-{ inherit x;
+{
+  inherit x;
   y = 456;
 }
 ```
@@ -62,15 +71,23 @@ is equivalent to
 
 ```nix
 let x = 123; in
-{ x = x;
+{
+  x = x;
   y = 456;
 }
 ```
 
-and both evaluate to `{ x = 123; y = 456; }`. (Note that this works
+and both evaluate to `{ x = 123; y = 456; }`.
-because `x` is added to the lexical scope by the `let` construct.) It is
+
-also possible to inherit attributes from another set. For instance, in
+> **Note**
-this fragment from `all-packages.nix`,
+>
+> This works because `x` is added to the lexical scope by the `let` construct.
+
+It is also possible to inherit attributes from another attribute set.
+
+Example:
+
+In this fragment from `all-packages.nix`,
 
 ```nix
 graphviz = (import ../tools/graphics/graphviz) {

doc/manual/src/language/operators.md

@@ -35,17 +35,14 @@
 
 ## Attribute selection
 
+> *attrset* `.` *attrpath* \[ `or` *expr* \]
+
 Select the attribute denoted by attribute path *attrpath* from [attribute set] *attrset*.
 If the attribute doesn’t exist, return the *expr* after `or` if provided, otherwise abort evaluation.
 
-<!-- FIXME: the following should to into its own language syntax section, but that needs more work to fit in well -->
+An attribute path is a dot-separated list of [attribute names](./values.md#attribute-set).
 
-An attribute path is a dot-separated list of attribute names.
+> *attrpath* = *name* [ `.` *name* ]...
-An attribute name can be an identifier or a string.
-
-> *attrpath* = *name* [ `.` *name* ]... \
-> *name* = *identifier* | *string* \
-> *identifier* ~ `[a-zA-Z_][a-zA-Z0-9_'-]*`
 
 [Attribute selection]: #attribute-selection
 

doc/manual/src/language/values.md

@@ -164,9 +164,17 @@ Note that lists are only lazy in values, and they are strict in length.
 
 An attribute set is a collection of name-value-pairs (called *attributes*) enclosed in curly brackets (`{ }`).
 
+An attribute name can be an identifier or a [string](#string).
+An identifier must start with a letter (`a-z`, `A-Z`) or underscore (`_`), and can otherwise contain letters (`a-z`, `A-Z`), numbers (`0-9`), underscores (`_`), apostrophes (`'`), or dashes (`-`).
+
+> *name* = *identifier* | *string* \
+> *identifier* ~ `[a-zA-Z_][a-zA-Z0-9_'-]*`
+
 Names and values are separated by an equal sign (`=`).
 Each value is an arbitrary expression terminated by a semicolon (`;`).
 
+> *attrset* = `{` [ *name* `=` *expr* `;` `]`... `}`
+
 Attributes can appear in any order.
 An attribute name may only occur once.
 
@@ -182,15 +190,19 @@ Example:
 
 This defines a set with attributes named `x`, `text`, `y`.
 
-Attributes can be selected from a set using the `.` operator. For
+Attributes can be accessed with the [`.` operator](./operators.md#attribute-selection).
-instance,
+
+Example:
 
 ```nix
 { a = "Foo"; b = "Bar"; }.a
 ```
 
-evaluates to `"Foo"`. It is possible to provide a default value in an
+This evaluates to `"Foo"`.
-attribute selection using the `or` keyword:
+
+It is possible to provide a default value in an attribute selection using the `or` keyword.
+
+Example:
 
 ```nix
 { a = "Foo"; b = "Bar"; }.c or "Xyzzy"