manual: use subheadings for primitive types
this gives us HTML anchors for each of them
This commit is contained in:
Valentin Gagarin
parent
86fcd4f692
commit
3063e5b94c
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@ -4,96 +4,98 @@
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Nix has the following basic data types:
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- *Strings* can be written in three ways.
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### Strings
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The most common way is to enclose the string between double quotes,
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e.g., `"foo bar"`. Strings can span multiple lines. The special
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characters `"` and `\` and the character sequence `${` must be
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escaped by prefixing them with a backslash (`\`). Newlines, carriage
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returns and tabs can be written as `\n`, `\r` and `\t`,
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respectively.
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*Strings* can be written in three ways.
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You can include the result of an expression into a string by
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enclosing it in `${...}`, a feature known as *antiquotation*. The
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enclosed expression must evaluate to something that can be coerced
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into a string (meaning that it must be a string, a path, or a
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derivation). For instance, rather than writing
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The most common way is to enclose the string between double quotes,
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e.g., `"foo bar"`. Strings can span multiple lines. The special
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characters `"` and `\` and the character sequence `${` must be
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escaped by prefixing them with a backslash (`\`). Newlines, carriage
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returns and tabs can be written as `\n`, `\r` and `\t`,
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respectively.
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```nix
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"--with-freetype2-library=" + freetype + "/lib"
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```
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You can include the result of an expression into a string by
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enclosing it in `${...}`, a feature known as *antiquotation*. The
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enclosed expression must evaluate to something that can be coerced
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into a string (meaning that it must be a string, a path, or a
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derivation). For instance, rather than writing
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(where `freetype` is a derivation), you can instead write the more
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natural
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```nix
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"--with-freetype2-library=" + freetype + "/lib"
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```
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```nix
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"--with-freetype2-library=${freetype}/lib"
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```
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(where `freetype` is a derivation), you can instead write the more
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natural
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The latter is automatically translated to the former. A more
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complicated example (from the Nix expression for
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[Qt](http://www.trolltech.com/products/qt)):
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```nix
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"--with-freetype2-library=${freetype}/lib"
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```
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```nix
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configureFlags = "
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The latter is automatically translated to the former. A more
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complicated example (from the Nix expression for
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[Qt](http://www.trolltech.com/products/qt)):
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```nix
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configureFlags = "
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-system-zlib -system-libpng -system-libjpeg
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${if openglSupport then "-dlopen-opengl
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-L${mesa}/lib -I${mesa}/include
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-L${libXmu}/lib -I${libXmu}/include" else ""}
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${if threadSupport then "-thread" else "-no-thread"}
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";
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```
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";
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```
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Note that Nix expressions and strings can be arbitrarily nested; in
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this case the outer string contains various antiquotations that
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themselves contain strings (e.g., `"-thread"`), some of which in
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turn contain expressions (e.g., `${mesa}`).
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Note that Nix expressions and strings can be arbitrarily nested; in
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this case the outer string contains various antiquotations that
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themselves contain strings (e.g., `"-thread"`), some of which in
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turn contain expressions (e.g., `${mesa}`).
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The second way to write string literals is as an *indented string*,
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which is enclosed between pairs of *double single-quotes*, like so:
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The second way to write string literals is as an *indented string*,
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which is enclosed between pairs of *double single-quotes*, like so:
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```nix
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''
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```nix
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''
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This is the first line.
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This is the second line.
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This is the third line.
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''
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```
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''
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```
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This kind of string literal intelligently strips indentation from
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the start of each line. To be precise, it strips from each line a
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number of spaces equal to the minimal indentation of the string as a
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whole (disregarding the indentation of empty lines). For instance,
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the first and second line are indented two spaces, while the third
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line is indented four spaces. Thus, two spaces are stripped from
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each line, so the resulting string is
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This kind of string literal intelligently strips indentation from
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the start of each line. To be precise, it strips from each line a
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number of spaces equal to the minimal indentation of the string as a
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whole (disregarding the indentation of empty lines). For instance,
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the first and second line are indented two spaces, while the third
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line is indented four spaces. Thus, two spaces are stripped from
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each line, so the resulting string is
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```nix
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"This is the first line.\nThis is the second line.\n This is the third line.\n"
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```
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```nix
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"This is the first line.\nThis is the second line.\n This is the third line.\n"
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```
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Note that the whitespace and newline following the opening `''` is
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ignored if there is no non-whitespace text on the initial line.
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Note that the whitespace and newline following the opening `''` is
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ignored if there is no non-whitespace text on the initial line.
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Antiquotation (`${expr}`) is supported in indented strings.
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Antiquotation (`${expr}`) is supported in indented strings.
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Since `${` and `''` have special meaning in indented strings, you
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need a way to quote them. `$` can be escaped by prefixing it with
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`''` (that is, two single quotes), i.e., `''$`. `''` can be escaped
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by prefixing it with `'`, i.e., `'''`. `$` removes any special
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meaning from the following `$`. Linefeed, carriage-return and tab
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characters can be written as `''\n`, `''\r`, `''\t`, and `''\`
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escapes any other character.
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Since `${` and `''` have special meaning in indented strings, you
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need a way to quote them. `$` can be escaped by prefixing it with
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`''` (that is, two single quotes), i.e., `''$`. `''` can be escaped
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by prefixing it with `'`, i.e., `'''`. `$` removes any special
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meaning from the following `$`. Linefeed, carriage-return and tab
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characters can be written as `''\n`, `''\r`, `''\t`, and `''\`
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escapes any other character.
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Indented strings are primarily useful in that they allow multi-line
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string literals to follow the indentation of the enclosing Nix
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expression, and that less escaping is typically necessary for
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strings representing languages such as shell scripts and
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configuration files because `''` is much less common than `"`.
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Example:
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Indented strings are primarily useful in that they allow multi-line
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string literals to follow the indentation of the enclosing Nix
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expression, and that less escaping is typically necessary for
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strings representing languages such as shell scripts and
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configuration files because `''` is much less common than `"`.
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Example:
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```nix
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stdenv.mkDerivation {
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```nix
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stdenv.mkDerivation {
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...
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postInstall =
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''
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@ -103,52 +105,60 @@ Nix has the following basic data types:
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${if enableBar then "cp bar $out/bin" else ""}
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'';
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...
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}
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```
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}
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```
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Finally, as a convenience, *URIs* as defined in appendix B of
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[RFC 2396](http://www.ietf.org/rfc/rfc2396.txt) can be written *as
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is*, without quotes. For instance, the string
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`"http://example.org/foo.tar.bz2"` can also be written as
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`http://example.org/foo.tar.bz2`.
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Finally, as a convenience, *URIs* as defined in appendix B of
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[RFC 2396](http://www.ietf.org/rfc/rfc2396.txt) can be written *as
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is*, without quotes. For instance, the string
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`"http://example.org/foo.tar.bz2"` can also be written as
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`http://example.org/foo.tar.bz2`.
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- Numbers, which can be *integers* (like `123`) or *floating point*
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(like `123.43` or `.27e13`).
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### Numbers
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Numbers are type-compatible: pure integer operations will always
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return integers, whereas any operation involving at least one
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floating point number will have a floating point number as a result.
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Numbers, which can be *integers* (like `123`) or *floating point*
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(like `123.43` or `.27e13`).
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- *Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at
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least one slash to be recognised as such. For instance, `builder.sh`
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is not a path: it's parsed as an expression that selects the
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attribute `sh` from the variable `builder`. If the file name is
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relative, i.e., if it does not begin with a slash, it is made
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absolute at parse time relative to the directory of the Nix
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expression that contained it. For instance, if a Nix expression in
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`/foo/bar/bla.nix` refers to `../xyzzy/fnord.nix`, the absolute path
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is `/foo/xyzzy/fnord.nix`.
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Numbers are type-compatible: pure integer operations will always
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return integers, whereas any operation involving at least one
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floating point number will have a floating point number as a result.
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If the first component of a path is a `~`, it is interpreted as if
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the rest of the path were relative to the user's home directory.
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e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
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whose home directory is `/home/edolstra`.
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### Paths
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Paths can also be specified between angle brackets, e.g.
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`<nixpkgs>`. This means that the directories listed in the
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environment variable `NIX_PATH` will be searched for the given file
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or directory name.
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*Paths*, e.g., `/bin/sh` or `./builder.sh`. A path must contain at
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least one slash to be recognised as such. For instance, `builder.sh`
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is not a path: it's parsed as an expression that selects the
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attribute `sh` from the variable `builder`. If the file name is
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relative, i.e., if it does not begin with a slash, it is made
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absolute at parse time relative to the directory of the Nix
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expression that contained it. For instance, if a Nix expression in
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`/foo/bar/bla.nix` refers to `../xyzzy/fnord.nix`, the absolute path
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is `/foo/xyzzy/fnord.nix`.
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Antiquotation is supported in any paths except those in angle brackets.
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`./${foo}-${bar}.nix` is a more convenient way of writing
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`./. + "/" + foo + "-" + bar + ".nix"` or `./. + "/${foo}-${bar}.nix"`. At
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least one slash must appear *before* any antiquotations for this to be
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recognized as a path. `a.${foo}/b.${bar}` is a syntactically valid division
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operation. `./a.${foo}/b.${bar}` is a path.
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If the first component of a path is a `~`, it is interpreted as if
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the rest of the path were relative to the user's home directory.
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e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
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whose home directory is `/home/edolstra`.
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- *Booleans* with values `true` and `false`.
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Paths can also be specified between angle brackets, e.g.
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`<nixpkgs>`. This means that the directories listed in the
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environment variable `NIX_PATH` will be searched for the given file
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or directory name.
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- The null value, denoted as `null`.
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Antiquotation is supported in any paths except those in angle brackets.
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`./${foo}-${bar}.nix` is a more convenient way of writing
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`./. + "/" + foo + "-" + bar + ".nix"` or `./. + "/${foo}-${bar}.nix"`. At
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least one slash must appear *before* any antiquotations for this to be
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recognized as a path. `a.${foo}/b.${bar}` is a syntactically valid division
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operation. `./a.${foo}/b.${bar}` is a path.
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### Booleans
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*Booleans* with values `true` and `false`.
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### Null
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The null value, denoted as `null`.
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## Lists
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