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authorLudovic Courtès <ludo@gnu.org>2020-03-06 11:25:43 +0100
committerLudovic Courtès <ludo@gnu.org>2020-03-12 18:32:15 +0100
commitcf2ac04f13d9266c7c8a2ebd2e85ef593231ac9d (patch)
tree409921980504c7138e4dac8769823fb50becc516 /doc/guix.texi
parentbe78906592c761aa2a67e979074561e459efdcac (diff)
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gexp: Add 'with-parameters'.
* guix/gexp.scm (<parameterized>): New record type. (with-parameters): New macro. (compile-parameterized): New gexp compiler. * tests/gexp.scm ("with-parameters for %current-system") ("with-parameters for %current-target-system") ("with-parameters + file-append"): New tests. * doc/guix.texi (G-Expressions): Document it.
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diff --git a/doc/guix.texi b/doc/guix.texi
index dd32b65fe0..4f8f7cfb2a 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -8022,6 +8022,25 @@ the second case, the resulting script contains a @code{(string-append
@dots{})} expression to construct the file name @emph{at run time}.
@end deffn
+@deffn {Scheme Syntax} with-parameters ((@var{parameter} @var{value}) @dots{}) @var{exp}
+This macro is similar to the @code{parameterize} form for
+dynamically-bound @dfn{parameters} (@pxref{Parameters,,, guile, GNU
+Guile Reference Manual}). The key difference is that it takes effect
+when the file-like object returned by @var{exp} is lowered to a
+derivation or store item.
+
+A typical use of @code{with-parameters} is to force the system in effect
+for a given object:
+
+@lisp
+(with-parameters ((%current-system "i686-linux"))
+ coreutils)
+@end lisp
+
+The example above returns an object that corresponds to the i686 build
+of Coreutils, regardless of the current value of @code{%current-system}.
+@end deffn
+
Of course, in addition to gexps embedded in ``host'' code, there are
also modules containing build tools. To make it clear that they are