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+%D \module
+%D   [       file=file-mod, % was supp-fil,
+%D        version=20110701, % 1995.10.10,
+%D          title=\CONTEXT\ File Macros,
+%D       subtitle=Resolvers,
+%D         author=Hans Hagen,
+%D           date=\currentdate,
+%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
+%C
+%C This module is part of the \CONTEXT\ macro||package and is
+%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
+%C details.
+
+\writestatus{loading}{ConTeXt File Macros / Resolvers}
+
+\unprotect
+
+\registerctxluafile{file-res}{1.001}
+
+%D \macros
+%D   {readfile,ReadFile}
+%D
+%D One cannot be sure if a file exists. When no file can be
+%D found, the \type{\input} primitive gives an error message
+%D and switches to interactive mode. The macro \type{\readfile}
+%D takes care of non||existing files. This macro has two faces.
+%D
+%D \starttyping
+%D \ReadFile {filename}
+%D \readfile {filename} {before loading} {not found}
+%D \stoptyping
+%D
+%D Many \TEX\ implementations have laid out some strategy for
+%D locating files. This can lead to unexpected results,
+%D especially when one loads files that are not found in the
+%D current directory. Let's give an example of this. In
+%D \CONTEXT\ illustrations can be defined in an external file.
+%D The resizing macro first looks if an illustration is defined
+%D in the local definitions file. When no such file is found,
+%D it searches for a global file and when this file is not
+%D found either, the illustration itself is scanned for
+%D dimensions. One can imagine what happens if an adapted,
+%D localy stored illustration, is scaled according to
+%D dimensions stored somewhere else.
+%D
+%D When some \TEX\ implementation starts looking for a file, it
+%D normally first looks in the current directory. When no file
+%D is found, \TEX\ starts searching on the path where format
+%D and|/|or style files are stored. Depending on the implementation
+%D this can considerably slow down processing speed.
+%D
+%D In \CONTEXT, we support a project||wise ordening of files.
+%D In such an approach it seems feasible to store common files
+%D in a lower directory. When for instance searching for a
+%D general layout file, we therefore have to backtrack.
+%D
+%D These three considerations have lead to a more advanced
+%D approach for loading files.
+%D
+%D We first present an earlier implementation of
+%D \type{\readfile}. This command backtracks parent
+%D directories, upto a predefined level. Users can change this
+%D level (on the commandline using a directive); we default to~3.
+%D
+%D We use \type{\normalinput} instead of \type{\input}
+%D because we want to be able to redefine the original
+%D \type{\input} when needed, for instance when loading third
+%D party libraries.
+
+\let\readfilename\empty
+
+\def\syst_files_read_file#protocol#path#name% #true #false
+  {\edef\readfilename{\clf_getreadfilename{#protocol}{#path}{#name}}%
+   \ifx\readfilename\empty
+     \expandafter\secondoftwoarguments
+   \else
+     \expandafter\syst_files_read_file_indeed
+   \fi}
+
+\def\syst_files_read_file_indeed#true#false%
+  {#true%
+   \relax
+   \normalinput{\readfilename}%
+   \relax}
+
+%D \macros
+%D   {readjobfile,readlocfile,readsysfile,
+%D    readfixfile,readsetfile}
+%D
+%D This implementation honnors the third situation, but we
+%D still can get unwanted files loaded and/or can get involved
+%D in extensive searching.
+%D
+%D Due to different needs, we decided to offer four alternative
+%D loading commands. With \type{\readjobfile} we load a local
+%D file and do no backtracking, while \type{\readlocfile}
+%D backtracks~\number\maxreadlevel\ directories, including the current
+%D one.
+%D
+%D System files can be anywhere and therefore
+%D \type{\readsysfile} is not bound to the current directory
+%D and obeys the \TEX\ implementation.
+%D
+%D Of the last two, \type{\readfixfile} searches on the
+%D directory specified and backtracks too, while
+%D \type{\readsetfile} does only search on the specified path.
+%D
+%D The most liberal is \type {\readfile}.
+
+\unexpanded\def\readjobfile     #name{\syst_files_read_file{job}    {.}{#name}} % current path, no backtracking
+\unexpanded\def\readlocfile     #name{\syst_files_read_file{loc}    {.}{#name}} % current path, backtracking
+\unexpanded\def\readsysfile     #name{\syst_files_read_file{sys}    {.}{#name}} % current path, obeys tex search
+\unexpanded\def\readfixfile#path#name{\syst_files_read_file{fix}{#path}{#name}} % specified path, backtracking
+\unexpanded\def\readsetfile#path#name{\syst_files_read_file{set}{#path}{#name}} % specified path, no backtracking
+\unexpanded\def\readfile        #name{\syst_files_read_file{any}    {.}{#name}}
+\unexpanded\def\ReadFile        #name{\syst_files_read_file{any}    {.}{#name}\donothing\donothing}
+
+%D So now we've got ourselves five file loading commands:
+%D
+%D \starttyping
+%D \readfile                {filename} {before loading} {not found}
+%D
+%D \readjobfile             {filename} {before loading} {not found}
+%D \readlocfile             {filename} {before loading} {not found}
+%D \readfixfile             {filename} {before loading} {not found}
+%D \readsysfile {directory} {filename} {before loading} {not found}
+%D \stoptyping
+
+\unexpanded\def\readtexfile#name#true#false%
+  {\pushcatcodetable
+   \catcodetable\ctxcatcodes
+   \readfile{#name}{#true}{#false}%
+   \popcatcodetable}
+
+\unexpanded\def\readxmlfile#name#true#false%
+  {\pushcatcodetable
+   \catcodetable\xmlcatcodes
+   \readfile{#name}{#true}{#false}%
+   \popcatcodetable}
+
+%D \macros
+%D   {doiflocfileelse,locfilename}
+%D
+%D \starttyping
+%D \doiflocfileelse {filename} {before loading} {not found}
+%D \stoptyping
+
+\unexpanded\def\doifelselocfile#name{\clf_doifelselocfile{#name}}
+           \def\locfilename    #name{\clf_locfilename    {#name}}
+
+\let\doiflocfileelse\doifelselocfile
+
+\protect \endinput