Checking if a file exists

[tueda]

It would be nice to have a functionality to check if a file exists in the path. One possibility of the syntax is

#if fileexists(foo.h)

#endif

The implementation should be easy, just opening and then closing the file. In this syntax, file names with ( and ) can't be handled properly, but I think this is the FORM way to discourage such crazy file names. Introducing some escapes for special characters in file names would be also easy.

There will be many way to use this file check. I'm considering usage as follows. Suppose I make a some library that have some table files. Table files can be in ASCII, which is the most portable way. But it will be faster if I use binary files (tablebase or *.sav storing expressions). Unfortunately they are most likely version-dependent. So I don't like to put the binary file in the library. Instead, I would prepare a way such that one can make them with his/her version of FORM. The library first tries to load a binary table and when impossible reads the corresponding ASCII table as a fallback. This is the way used in a Mathematica package MT.

[vermaseren]

Sounds like a good idea Jos

…

On 23 Nov 2017, at 12:05, Takahiro Ueda ***@***.***> wrote: It would be nice to have a functionality to check if a file exists in the path. One possibility of the syntax is #if fileexists(foo.h) #endif The implementation should be easy, just opening and then closing the file. In this syntax, file names with ( and ) can't be handled properly, but I think this is the FORM way to discourage such crazy file names. Introducing some escapes for special characters in file names would be also easy. There will be many way to use this file check. I'm considering usage as follows. Suppose I make a some library that have some table files. Table files can be in ASCII, which is the most portable way. But it will be faster if I use binary files (tablebase or *.sav storing expressions). Unfortunately they are most likely version-dependent. So I don't like to put the binary file in the library. Instead, I would prepare a way such that one can make them with his/her version of FORM. The library first tries to load a binary table and when impossible reads the corresponding ASCII table as a fallback. This is the way used in a Mathematica package MT <https://arxiv.org/abs/1307.6925>. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#240>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFLxEvZ2P74Fg_KRFI50tNHk0j9VRILsks5s5VF7gaJpZM4QolMC>.

[tueda]

hasinclude macro might be useful. It expands to the file path if it exists in the include paths; otherwise, it expands to an empty string.

#if `hasinclude(foo.h)'
  #include foo.h
#else
  #message foo.h is not found
  #terminate
#endif

A non-trivial use case is caching. For example:

#if `hasinclude(cachefile)`
  #include cachefile
#else
* Perform a computation and write the result to cachefile.
#endif

Maybe we can also add a similar fileexists macro to simply check if a given file exists (e.g., for #241).