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| Allegro CL version 10.1 Unrevised from 10.0 to 10.1. 10.0 version

## file-incompatible-fasl-error

This is the class of condition signaled when an attempt is made to load an incompatible fasl file into a running Lisp. This can happen in two ways:

1. The internal version of the fasl file is incompatible with the lisp that is loading it. The version number is set when an Allegro CL release is made. The actual number is not the same as the release number (thus the fasl version number for Allegro CL release 8.1 is not "8.1"), but the fasl version is usually incremented with each release and all files must be recompiled when moving from one release to a later release (from release 8.0 to release 8.1, for example).

   The internal fasl version number is stored in the fasl file but not in a way that can be read by humans. If you want to find out in gross terms if your file foo.fasl is compatibe with your lisp, type head -4 foo.fasl into most UNIX shells, or into cygwin on Windows (some versions of head might require a different style of specifying only 4 lines). The first 4 lines of the fasl file are (mostly) human readable starting with "<AcL>" (if such a string doesn't appear on the first line, then it is likely either a corrupted file or a fasl generated by another Lisp implementation).

   The second line will contain the string identifying the lisp which compiled it. It will include a Lisp version, an architecture, and a date. If the first two items don't match what startup information is printed on your Lisp, then it is the likely cause of the error.

2. Certain architectures (e.g. x86, x86-64) are the underlying architecture for several operating systems. Fasl files produced on one might be loadable on another. In general, the non-windows Lisps of the same architecture allow their fasl files to be loaded into each other's Lisps, so the `file-incompatible-fasl-error` condition cannot be counted on to distinguish different Lisps. However this error will be generated whenever an attempt is made to load a Windows fasl file into a non-Windows Lisp, or to load a non-Windows fasl file into a Windows Lisp.

This is not the error signaled when trying to load a fasl file generated on one architecture into a Lisp running on another architecture.

See errors.htm for general information on errors in Allegro CL.

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This page was not revised from the 10.0 page.
Created 2019.8.20.

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| Allegro CL version 10.1 Unrevised from 10.0 to 10.1. 10.0 version