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README.md

HTML report generator for plancknull

This project provides a HTML report generator for the data produced by the program plancknull. It is written using Chicken Scheme.

The program takes as input a JSON database (usually produced by plancknull) which specifies the type of tests that must be included in the report. Its output is a self-contained HTML report that can be distributed (it does not have external references).

How to generate the executable

The program is written in Scheme R5RS, and it needs to be compiled into an executable in order to be executed. There are two ways to do it: either grab a precompiled binary (easy way) or compile it by yourself (hard way). In the following section we'll detail the two procedures.

Grabbing the executable (easy way)

You can ask Maurizio Tomasi for a self-contained bundle. At the LFI DPC and at NERSC, he keeps one in his homedir. The bundle is a directory containing the executable (named standalone_generator) and a large set of dynamic libraries needed to run the program. You can move this directory anywhere in your filesystem, but do not try to run it on different architectures/distributions (e.g. from a RedHat system to Ubuntu, from x86 to x86_64...).

Compiling the executable from the source (hard way)

To compile the source code into an executable you must have the Chicken Scheme compiler and a few open-source libraries for Chicken (called eggs). To install Chicken, you can use your package manager (e.g. sudo apt-get install chicken-bin under Ubuntu Linux) if you are a sudo user. Otherwise, you must install it from source in your home directory. Open a terminal and run the following commands:

mkdir -p $HOME/usr $HOME/.chicken-temp
curl http://code.call-cc.org/releases/current/chicken.tar.gz | tar xz -C $HOME/.chicken-temp
pushd $HOME/.chicken-temp/chicken-*
make PLATFORM=linux PREFIX=$HOME/usr install
popd
rm -rf $HOME/.chicken-temp

(If you want, you can change $HOME/usr with any other directory you want. It should be the place where you usually install things under your home directory.) At this point, if you did not so already, put the following lines at the end of your ~/.profile (assuming you're using sh, bash or dash as your login shell):

export PATH=$HOME/usr/bin:$PATH
export C_INCLUDE_PATH=$HOME/usr/include:$C_INCLUDE_PATH
export LIBRARY_PATH=$HOME/usr/lib:$LIBRARY_PATH
export LD_LIBRARY_PATH=$HOME/usr/lib:$LD_LIBRARY_PATH
export MANPATH=$HOME/usr/man:$MANPATH

Logout and login to see the new variabiles. If you are able to run chicken -version, then the installation of the compiler completed successfully.

Now you need some "eggs" (that is, Chicken's libraries). Move to the directory where you have the source code of plancknull_generate_html and run the following command:

sudo make install_eggs

(If you've installed Chicken under your homedir, omit sudo). Now you should be able to compile the program, simply run

make generator

This will silently convert generator.scm into a C program, which will then be compiled to a standalone executable. The Makefile provided with the source code allows for many targets, run make TARGET where TARGET is one of the following:

  • generator produces the executable. Be careful that this program needs the Chicken runtime libraries to be accessible at runtime (therefore you cannot distribute it)
  • deploy produces a stand-alone executable in the directory standalone_generator. Unlike the generator target, the content of the directory (containing the executable standalone_generator plus many dynamic libraries) can be distributed to others, as all the Chicken libraries needed by the program are included in the directory. (You can think of it as Chicken's analogous to Mac OS X .app directories.)
  • install_eggs repeatedly calls chicken-install to install the eggs required to compile the program. You might have to use sudo (e.g. this is the case if you installed Chicken using Ubuntu's apt-get).
  • documentation runs Schematic on the source code to produce this documentation (in the docs directory).
  • help prints a summary of the available options implemented in the makefile.

How to run the program

To run the program, you must have the following programs available in your PATH:

The program needs as input one or more JSON files containing information about the products of the null tests. Typically, these are produced by the plancknull program. You specify the directory containing the output of plancknull as the first parameter of the program, followed by the directory where to save the report:

$ generator NULL_TEST_DIRECTORY OUTPUT_PATH

(If you are using the standalone executable, run plancknull_generate_html_* instead of generator). This will read the results of the null tests from the subdirectories under NULL_TEST_DIRECTORY, then it will populate the directory OUTPUT_PATH with the files needed for the HTML report. If OUTPUT_PATH does not exist, it will be silently created.

How to read the source code of this program

The source code of the program can be processed using schematic, a documenting tool for Chicken Scheme, in order to have some nicely formatted HTMLs. Install it from the command line with the command sudo chicken-install schematic, then run

schematic -f markdown generator.scm

(assuming you have markdown, which can be easily installed using apt-get under Debian/Ubuntu). This will create a sub-directory html where you'll find the source code of this very webpage.

The output of schematic is also available at http://ziotom78.github.com/plancknull_generate_html/.

Appendix: a very short introduction to Scheme

To help the reader who has never read Scheme code, I am summarizing here the main characteristics of the language. This is not a Scheme tutorial, just a general introduction written for people that are already proficient with some other language (in the text there are many references to Python). If you are not interested in reading the source code of this program, you can skip this section.

Chicken Scheme implements the R5RS standard of Scheme, a language derived from LISP. Scheme is a really simple language (the language and the standard library are described together by a 50-page document: compare this with Python 2.7, which needs 127 A4 pages for the language plus 1366 pages for the standard library). This simplicity derives from three facts:

  1. The syntax is extremely simple: apart from letters and numbers, the only symbols which have special meaning for the compiler are (, ), quote, backtick, comma (rarely used) and whitespaces (plus ;, which starts a comment).
  2. The standard library is quite small. Clearly this is not an advantage, but Chicken Scheme provides a broad selection of extensions, called "eggs", that mitigate this problem.
  3. No complex features of high-end languages are specified by the standard. For instance, a typical Python program uses OOP techniques, which are grounded on many non-trivial concepts (object encapsulation, inheritance, abstract methods, static methods...). You can easily extend Scheme to support OOP through its powerful macro system, but we won't do this in this program.

Scheme is based on the concept of list, which is a series of elements separated by spaces and enclosed within parentheses, like (1 2 3). Function calls are lists where the first element is the function and the others are the parameters. E.g., to calculate the sinus of 0.1 you write (sin 0.2), to print a string you write (print "Hello, world!"). By default, a list is always interpreted as a function call, unless there is a ' before the open parenthesis. So (sin 0.1) calculates the sinus of 0.1, but '(sin 0.1) is a list of two elements: the first is the sin function, the second is the number 0.1. Therefore, in Scheme program and data share the same representation, and you can easily convert one into another (using e.g. eval: (eval '(sin 0.1)) is the same as (sin 0.1), but in the first case you can build your list programatically).

The parenthesis syntax is used everywhere, also in mathematical expressions ("infix notation", sometimes known as "reverse Polish notation"). To calculate 5 * (1 + 2 + 3) you write (* 5 (+ 1 2 3)). (Note that both * and + are used like any other function call.)

Function and variable definition share the same syntax: you have to use define. For instance, (define x 1) creates a new variable which contains the integer 1, while (define (f x) (* 2 x)) defines a function f which accepts one parameter x and which returns x doubled.

Similarly to Python, anonymous functions can be defined using lambda. Unlike Python, Scheme's lambda expressions can contain any sequence of instructions.

Loops can be implemented using either recursion (a "functional" construct) or do (an "imperative" construct). However, for simple programs like the one we are describing here, we only rely on functions like map and filter, which are analogous to Python's counterparts.

To end with an example, consider this quite idiomatic Python code:

print ", ".join([x.upper() for x in ("a", "b", "c")])

which prints "A, B, C". It can be translated in Chicken Scheme:

(string-intersperse (map string-upcase
                         '("a" "b" "c"))
                    ", ")

While Python uses many different syntactic elements (dot, parentheses, brackets, the for and in keyword, explicit naming of the x variable), everything in this Scheme snipped follows the same idea of using parentheses to indicate both function calls and lists.

(In Scheme you usually use much more newlines than in imperative programs. This helps in visualizing which arguments are parts of which list, as it is easy to get confused by nested parentheses. In the following of this document, you can highlight parentheses on the code on the right by moving the mouse over it.)

Scheme's syntax can look weird at first, but it is grounded on two very simple elements: parentheses (which group elements) and white spaces (which separate elements within parentheses). Compare this with e.g. Python, where there are many symbols to be used in a program: () identifies a tuple (or the parameters in a function call), [] a list, {} a dictionary, : introduces a sub-loop or a definition, ; separates statements in the same line, etc. And there are some strange quirks in the language, e.g. you have to remember that a one-element list can be written as [1], but for a one-element tuple you must append a comma: (1,).

HTML generation and Scheme

Thanks to its powerful macro system, Scheme (and LISP languages in general) is very good in handling HTML, see e.g. Paul Graham's 16th chapter of ANSI Common LISP. The Chicken's library html-tags implements HTML-like commands in Scheme, which are converted into strings. (A more sophisticated approach would use one of the many Chicken's SXML libraries.) The idea is that every time you have some HTML tag in the form <tag>...</tag>, you write it as the Scheme command (<tag> ...), where parentheses are used to delimit the tag. This command is converted into a string, that can then be printed on screen. Here is an example:

(require-extension html-tags)
(print (<h1> (format #f "The result of the sum is ~a" (+ 3 6))))

Note that we can call Scheme functions like format and + within the HTML tags. This program will print

<h1>The result of the sum is 9</h1>

This differs substantially from the typical approach of using a template library like Python's Jinja2 library or Django: in that case, you write a HTML template interspersed with Jinja2's internal language (which, although similar, is not Python: see e.g. the use of the | operator) - the same applies to Django as well. Thus, you have to learn a new language (other than Python and HTML) to use it. With Scheme, we're using it for everything!

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