nixo
/
guix-devel
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

doc: Update gexp wrt. extensibility. 

This is a followup to bcb1328.

* doc/guix.texi (G-Expressions): Move paragraph about extensibility
  below.  Remove assumptions that things are either packages or
  derivations.
This commit is contained in:
Ludovic Courtès 2015-03-28 21:16:36 +01:00
parent 065b795497
commit b39fc6f7bc
1 changed files with 16 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
doc/guix.texi
View File

@ -2490,13 +2490,9 @@ Gexps are meant to be written to a file and run or manipulated by other
processes. processes.
@item @item
When a package or derivation is unquoted inside a gexp, the result is as When a high-level object such as a package or derivation is unquoted
if its output file name had been introduced. inside a gexp, the result is as if its output file name had been
introduced.
Actually this mechanism is not limited to package and derivation
objects; @dfn{compilers} able to ``lower'' other high-level objects to
derivations can be defined, such that these objects can also be inserted
into gexps.
@item @item
Gexps carry information about the packages or derivations they refer to, Gexps carry information about the packages or derivations they refer to,
@ -2504,6 +2500,11 @@ and these dependencies are automatically added as inputs to the build
processes that use them. processes that use them.
@end itemize @end itemize
Actually this mechanism is not limited to package and derivation
objects; @dfn{compilers} able to ``lower'' other high-level objects to
derivations can be defined, such that these objects can also be inserted
into gexps.
To illustrate the idea, here is an example of a gexp: To illustrate the idea, here is an example of a gexp:
@example @example
@ -2563,24 +2564,24 @@ or more of the following forms:
@table @code @table @code
@item #$@var{obj} @item #$@var{obj}
@itemx (ungexp @var{obj}) @itemx (ungexp @var{obj})
Introduce a reference to @var{obj}. @var{obj} may be a package or a Introduce a reference to @var{obj}. @var{obj} may have one of the
supported types, for example a package or a
derivation, in which case the @code{ungexp} form is replaced by its derivation, in which case the @code{ungexp} form is replaced by its
output file name---e.g., @code{"/gnu/store/@dots{}-coreutils-8.22}. output file name---e.g., @code{"/gnu/store/@dots{}-coreutils-8.22}.
If @var{obj} is a list, it is traversed and any package or derivation If @var{obj} is a list, it is traversed and references to supported
references are substituted similarly. objects are substituted similarly.
If @var{obj} is another gexp, its contents are inserted and its If @var{obj} is another gexp, its contents are inserted and its
dependencies are added to those of the containing gexp. dependencies are added to those of the containing gexp.
If @var{obj} is another kind of object, it is inserted as is. If @var{obj} is another kind of object, it is inserted as is.
@item #$@var{package-or-derivation}:@var{output} @item #$@var{obj}:@var{output}
@itemx (ungexp @var{package-or-derivation} @var{output}) @itemx (ungexp @var{obj} @var{output})
This is like the form above, but referring explicitly to the This is like the form above, but referring explicitly to the
@var{output} of @var{package-or-derivation}---this is useful when @var{output} of @var{obj}---this is useful when @var{obj} produces
@var{package-or-derivation} produces multiple outputs (@pxref{Packages multiple outputs (@pxref{Packages with Multiple Outputs}).
with Multiple Outputs}).
@item #+@var{obj} @item #+@var{obj}
@itemx #+@var{obj}:output @itemx #+@var{obj}:output