done lang/c.py, added README

+codanim: Animated code & data structures with LaTeX/beamer 
+
+  (C) 2020 Franck Pommereau <franck.pommereau@univ-evry.fr>
+      This is free software, see file LICENCE
+
+codanim allows to generate LaTeX/TikZ code to animate source code and
+data structures for beamer presentations. So far, it is oriented to
+simulate C code, but there is no conceptual limitation for the
+simulation of other languages.
+
+codanim is currently highly experimental and neither well documented
+nor well tested. You've been warned.
+
+## INSTALL
+
+There is so far no installation procedure. Just copy directory
+`codanim` somewhere in your `PYTHONPATH`.
+
+File `examples/pygments.sty` will be needed to compile the final LaTeX
+files. File `examples/tpl.tex` shows how the generated LaTeX code may
+be included in a beamer presentation.
+
+## CONCEPTS
+
+codanim defines Python classes to simulate the data and control-flow
+structures of an imperative language. Data structures are defined in
+`codanim.data` and include:
+
+ * `Pointer(data)` a pointer to another data `data`
+ * `Value(value)` an arbitrary value, initialised to `value`. If
+   `value` is `None` (the default), the value is considered
+   uninitialised
+ * `Array(init, index=[])` an array of values, that is zero-indexed,
+   and initialised as follows:
+    * if `init` is an `int`, then it is the length of the array whose
+      values are all uninitialised
+    * if `init` is a `list` then is holds the initial values of the
+      array
+   `index` is a list of variables identifiers that may be used to
+   access the array cells (see below)
+ * `Struct(init)` a structure whose fields and initial values are
+   defined by `init` that must be a `dict`
+ * `Heap()` a container for dynamically allocated data that provides
+   methods `new` and `free` to do so
+
+Control-flow structures are used to simulate within Python code that
+may potentially be written in any imperative language. Doing so, all
+the changes that are made to the data structures defined above are
+recorded so that they may be latter animated, consistently with the
+animation of the code itself. The idea is that source code in the
+simulated language is split into corresponding control-flow
+structures, and actual computation is done using equivalent Python
+code instead of executing the code in the source language.
+Control-flow structures are defined in `codanim.flow` and include:
+
+ * `RAW(src='...')` raw code from the simulated language, its
+   simulation is no-op, but it is rendered highlighted in the final
+   animation
+ * `WS(src='...')` just like `RAW` but should be only white spaces (so
+   that it won't be highlighted)
+ * `BLOCK(*body)` a group of other structures that are simulated (and
+   rendered) sequentially
+ * `STMT(*steps, src='...')` an arbitrary statement that is simulated
+   by running its`steps` sequentially, each of which being an
+   arbitrary Python statement that is `exec`ed
+ * `EXPR(expr, src='...')` an arbitrary Python expression `expr` that
+   simulate an expression in the simulated language
+ * `PY(code)` an arbitrary Python statement that need to be executed
+   but is not rendered in the final animation, just like every
+   structure that expects no `src='...'` argument
+ * `ENV(name, value)` a data structure that need to be defined in
+   order to do the simulation (typically: global or external
+   variables), and which is stored into variable `name` that can be
+   used from the Python code of statements and expression
+ * `DECL(name, init=None, animate=False, src'...')` an actual variable
+   declaration in the simulated language, that will be executed and
+   rendered. The execution consists of evaluating `init` that should
+   be an `EXPR` (or `None`) and assigning its value to `name`. If
+   `animate` is `True` then the value of the variable will displayed
+   within a comment just next to the declaration in the final
+   animation
+ * `XDECL(*names, src='...')` several uninitialised declarations
+ * `BREAK` a `break` instruction for loops and switches
+ * `RETURN(value, src='...')` a return instruction from a function
+ * `IF(cond, then, otherwise=None, src='...')` simulates an `if` block
+   with an optional `else` part (called `otherwise` since `else` is a
+   Python keyword. Argument `cond` should be an `EXPR` instance
+ * `WHILE(cond, body, src='...')` simulates a `while` loop
+ * `DO(body, cond, src='...')` simulates a `do/while` loop
+ * `FOR(init, cont, step, body)` simulates a C-like `for` loop
+ * `FUNC(body, src='...')` simulates a function
+   **TODO:** functions calls is not implemented yet, so basically, a
+   function is so far only a `BLOCK` with source code
+ * `SWITCH(cond, *cases, src='...')` simulates a C-like switch,
+   `cases` may be:
+   * `CASE(value, body)` to simulate a `case` statement
+   * `DEFAULT()` to simulate a `default` statement
+
+So, all what you need is to defined some data structures, some
+control-flow structures with appropriate `src` arguments (so that code
+is rendered in the simulated language), and with appropriate Python
+code to simulate the original statements and expressions.
+
+Writing the control-flow structures may be tedious, so codanim may be
+called from the command line to parse actual code to be simulated and
+generate the appropriate control-flow structures (in which the Python
+code remains to be written). Run `python -m codanim` for help.
+
+## EXAMPLES
+
+File `examples/Makefile` can be used to build the PDF for all the
+examples. For instance use `make heap.pdf` to build the first example
+described below.
+
+### `examples/heap.py`
+
+It defines a `Heap` instance and add chained `Struct`s to it. The
+final picture is rendered as TikZ code. There is no animation, this is
+just the picture of a chained list.
+
+### `examples/stack-push.py`
+
+It uses the same kind of linked lists as above, seen as stacks, to
+animate a push onto a stack. First the data is defined, then the
+control-flow structure. The latter is then simulated and finally, both
+code and data structures are rendered for LaTeX/beamer inclusion.
+
+Note the use of class `Box` that can be used to layout several data
+structures.
+
+### `examples/qs-partition.py` and `examples/qs-main.py`
+
+The partitioning and main algorithm of a quick-sort. This shows how to
+use `Array`, in particular the `index` argument. `qs-main` also shows
+how to define custom layout of arrays, as well as auxiliary Python
+functions to simulate full C-functions calls in one step.

+import argparse, pathlib, importlib, sys
+from . import lang as _lang
+
+languages = {}
+
+for path in pathlib.Path(_lang.__file__).parent.glob("*.py") :
+    module_name = path.with_suffix("").name
+    if module_name == "__init__" :
+        continue
+    module = importlib.import_module(f".lang.{module_name}", package="codanim")
+    languages[module_name.lower()] = module
+
+class ListLang (argparse.Action) :
+    def __call__ (self, parser, *l, **k) :
+        print("Supported languages:")
+        width = max(len(l) for l in languages) + 4
+        for lang, module in sorted(languages.items()) :
+            print((" - {lang:<%s} {help}" % width).format(lang=lang,
+                                                          help=module.translate.__doc__))
+        parser.exit(0)
+
+parser = argparse.ArgumentParser(
+    prog="codanim",
+    description="parse code and generate Python stub suitable for codanim")
+
+parser.add_argument("-l", "--lang",
+                    default=None,
+                    help="language to be parsed (default: guess from file name)")
+parser.add_argument("-L", "--list-lang", nargs=0,
+                    action=ListLang,
+                    help="list supported languages")
+parser.add_argument("-o", "--output", type=argparse.FileType("w"),
+                    default=sys.stdout,
+                    help="output file")
+parser.add_argument("SOURCE", type=argparse.FileType("r"),
+                    help="source file")
+args = parser.parse_args()
+
+if args.lang is None :
+    args.lang = args.SOURCE.name.rsplit(".")[-1]
+
+args.lang = args.lang.lower()
+
+if args.lang not in languages :
+    parser.error("unsupported language: %r" % args.lang)
+
+translate = languages[args.lang].translate
+
+args.output.write(repr(translate(args.SOURCE.read())) + "\n")

@@ -385,3 +385,13 @@ class Translator (object) :
         return default
     def do_Break (self, node) :
         return flow.BREAK()
+
+##
+## CLI interface
+##
+
+def translate (code) :
+    "the C language"
+    a = parse(code)
+    t = Translator()
+    return t(a)