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authorLudovic Courtès <ludo@gnu.org>2017-11-14 10:16:22 +0100
committerLudovic Courtès <ludo@gnu.org>2020-05-16 00:34:41 +0200
commit644cb40cd83eff8a5bcdbd2d63887daa18228f41 (patch)
treee470f35ad20a8ad6805d2a8e7b03897bc10f6098 /doc
parentd03001a31a6d460b712825640dba11e3f1a53a14 (diff)
gexp: Add 'let-system'.
* guix/gexp.scm (<system-binding>): New record type. (let-system): New macro. (system-binding-compiler): New procedure. (default-expander): Add 'self-quoting?' case. (self-quoting?): New procedure. (lower-inputs): Add 'filterm'. Pass the result of 'mapm/accumulate-builds' through FILTERM. (gexp->sexp)[self-quoting?]: Remove. * tests/gexp.scm ("let-system", "let-system, target") ("let-system, ungexp-native, target") ("let-system, nested"): New tests. * doc/guix.texi (G-Expressions): Document it.
Diffstat (limited to 'doc')
-rw-r--r--doc/guix.texi26
1 files changed, 26 insertions, 0 deletions
diff --git a/doc/guix.texi b/doc/guix.texi
index a36b9691fb..d043852ac3 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -8123,6 +8123,32 @@ 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} let-system @var{system} @var{body}@dots{}
+@deffnx {Scheme Syntax} let-system (@var{system} @var{target}) @var{body}@dots{}
+Bind @var{system} to the currently targeted system---e.g.,
+@code{"x86_64-linux"}---within @var{body}.
+
+In the second case, additionally bind @var{target} to the current
+cross-compilation target---a GNU triplet such as
+@code{"arm-linux-gnueabihf"}---or @code{#f} if we are not
+cross-compiling.
+
+@code{let-system} is useful in the occasional case where the object
+spliced into the gexp depends on the target system, as in this example:
+
+@example
+#~(system*
+ #+(let-system system
+ (cond ((string-prefix? "armhf-" system)
+ (file-append qemu "/bin/qemu-system-arm"))
+ ((string-prefix? "x86_64-" system)
+ (file-append qemu "/bin/qemu-system-x86_64"))
+ (else
+ (error "dunno!"))))
+ "-net" "user" #$image)
+@end example
+@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