LIM Home Page

Copyright © 1997, Digital Equipment Corporation. All rights reserved.

Overview

LIM is a text processing language in the general family of lex, yacc, sed, awk, and trans, but is based on Dijkstra's calculus of guarded commands. The name is an acronym for Language of the Included Miracle, because LIM programs can violate the so-called Law of the Excluded Miracle. For details see "A Discipline of Programming", Edsger W. Dijkstra, Prentice-Hall, 1976, and "A generalization of Dijkstra's calculus", Greg Nelson, Trans. on Programming Languages and Systems, October 1989, or SRC Research Report 16.

A LIM command may be guarded by a predicate. The command is said to fail if the predicate is false when the command is executed. The main novelty in LIM is that failing commands never have side effects. If a long computation has side effects and then fails, it is as though the side effects never happened. This property of the language makes it easy to write parsers and pretty-printers, since they require the ability to speculatively perform some action. In fact, the LIM distribution includes a pretty-printer for the LIM language that is itself written in LIM.

Downloading LIM

LIM is written in C, and uses lex/yacc or flex/bison. It has been successfully built on the Digital Ultrix and Digital Unix operating systems. It should compile on most other Unix platforms.

To download LIM, follow these steps:

• Make a new directory called "lim".

• Select the following link, and tell your browser to save the downloaded file to your new "lim" directory:

  lim.tar.Z

• cd into your new "lim" directory. It should contain the single file "lim.tar.Z". If it instead contains the file "lim.tar", then your browser has automatically uncompressed the file, and you can skip the following step.

• Run "uncompress lim.tar.Z" on the downloaded file.

• Run "tar xvf lim.tar" on the resulting tar file to extract the LIM sources.

• Run "rm lim.tar" to remove the tar file.

Installing LIM

Once you have downloaded and unpacked the LIM sources, follow these steps from your "lim" directory to build LIM on your system:

• The LIM pretty-printer, pplim, requires that three LIM programs be installed in a centralized lib directory. By default, pplim expects these scripts to be installed in /usr/local/lib/lim. If you plan to install them somewhere else, edit the file "pp/pplim.sh. Replace the pathname "/usr/local/lib/lim" on the third line of that script with the absolute path of the directory where you eventually plan to install the scripts.

• From your "lim" directory, run "make". This will create a derived directory named by your machine's architecture. It's name is formed by running "machine".

• You may now want to copy the LIM executables, man pages, and library files to centralized bin, man, and lib directories. If your derived directory is denoted by arch, the files you may want to copy are:

  To centralized bin:

  • arch/lim - LIM executable
  • arch/pplim - LIM pretty-printer

  To centralized man/man1:

  • lim.1 - lim(1) man page
  • pp/pplim.1 - pplim(1) man page

  To centralized lib/lim:

  • pp/format.lim - formats pretty-printer output
  • pp/lex.lim - parses input for pretty-printer
  • pp/pp.lim - LIM pretty-printer

  The directory in which the last three files are installed should match the directory in the pp/pplim.sh script that you edited in the first step of this section.

Once you have successfully installed lim, you may be interested in downloading and installing mtex, a set of LIM scripts for producing man pages in HTML and nroff format from a single LaTeX-like source format. For more information about mtex, see the mtex home page.

[ Systems Research Center (SRC) Software Home Page ]

Last modified on Thu Aug 28 22:46:04 PDT 1997 by heydon