Commit 1b964925 authored by simonpj's avatar simonpj
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[project @ 1999-08-24 09:31:07 by simonpj]

Document the -i effect on recompilation
parent 7d845299
......@@ -508,6 +508,8 @@ it looks.
<tag>@-i<dirs>@</tag><nidx>-i&lt;dirs&gt; option</nidx> This flag
prepends a colon-separated list of @dirs@ to the ``import
directories'' list.
See also Section <ref id="recomp"> for the significance of using
relative and absolute pathnames in the @-i@ list.
<tag>@-i@</tag> resets the ``import directories'' list back to nothing.
......@@ -614,18 +616,24 @@ signature within the interface file. It also keeps in every interface
file a list of the version numbers of everything it used when it last
compiled the file. If the source file's modification date is earlier
than the @.o@ file's date (i.e. the source hasn't changed since the
file was last compiled), and you give GHC the @-recomp@<nidx>-recomp
option</nidx> flag, then GHC will be clever. It compares the version
file was last compiled), GHC will be clever. It compares the version
numbers on the things it needs this time with the version numbers on
the things it needed last time (gleaned from the interface file of the
module being compiled); if they are all the same it stops compiling
rather early in the process saying ``Compilation IS NOT required''.
What a beautiful sight!
It's still an experimental feature (that's why @-recomp@ is off by
default), so tell us if you think it doesn't work.
Patrick Sansom has a workshop paper about how all this is done. Ask
GHC <em>only</em> keeps detailed dependency information for ``user'' modules,
not for ``library'' modules. It distinguishes the two by a hack: a module
whose @.hi@ file has an absolute path name is considered a library module,
while a relative path name indicates a user module. So if you have a
multi-directory application, use <em>relative</em> path names in your
@-i@ path, to force GHC to record detailed dependency information.
Use absolute path names only for directories containing slowly-changing
library modules.
Patrick Sansom had a workshop paper about how all this is done (though
the details have changed quite a bit). Ask
him (email: <htmlurl name="sansom@@dcs.gla.ac.uk"
url="mailto:sansom@@dcs.gla.ac.uk">) if you want a copy.
......
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