==== Larch: a simple macro language for scientific programming ====

Larch is a macro language intended to be embedded in scientific applications.

The symbol table is also much simpler. The basic approach of this version of larch is to convert input larch program text, and convert it to valid python code (inputText.py). This python code is then parsed into an AST tree (compiler.py), which is then interpreted using a simple interpreter that uses a local symbol table (symbolTable.py) for name lookup and resolution.

By itself, this gives several benefits:

1. the intermediate python code can be saved so that code validation and translation of larch to python are now trivial

2. the parsed AST tree is guaranteed (at least as far as python itself is) to be correct.

3. Interpreting the AST tree is very simple, including all loop and control-flow code, and the resulting compiler.py is very much simpler than the earlier version.

In addition, the symbol table is simplified so that a symbolTable contains python objects and Groups (simple containers for other objects and Groups). Namespaces are built simply usin attributes of the Group class. That is, attribute lookup is heavily used, and symbols just python objects.

Special Larch-specific objects (defined variable, procedures) are just constructed as classes, and so no special Symbol class is needed.

=== Syntax differences between LARCH and Python ====

1. larch does not use indentation level. Rather a block is ended with one of 'end', '#end', 'endXXX', or '#endXXX' for XXX = 'if', 'for', 'def', 'while', 'try'

   The '#end' version allows code to be both valid larch and python.

2. a Defined Variable can be defined with def [symbol_name] = expression

   In larch->python translation, this is converted to _builtin.definevar('symbol_name','expression') which creates a DefinedVariable() instance that stores the ast representation of the expression.

   On each name lookup for a DefinedVariable(), the expression is re-evaluated and the appropriate value inserted.

3. command syntax is allowed in some cases, so that parentheses are not required for all function calls.

   If the first word of a line of code contains a word that is is a valid symbol name (and not a reserved word) and the second word that is either a valid name or a number, and if the line does not end with a ')', the first word is taken as a function name and parentheses are added, so that command arg1, arg2 => command(arg1, arg2) and so on.