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.. include:: links.rst
Rationale
---------
|TatSu| was created to address some recurring problems encountered
over decades of working with parser generation tools:
- Some programming languages allow the use of *keywords* as
identifiers, or have different meanings for symbols depending on
context (`Ruby`_). A parser needs control of lexical analysis to be
able to handle those languages.
- LL and LR grammars become contaminated with myriads of lookahead
statements to deal with ambiguous constructs in the source language.
`PEG`_ parsers address ambiguity from the onset.
- Separating the grammar from the code that implements the semantics,
and using a variation of a well-known grammar syntax (`EBNF`_) allows
for full declarative power in language descriptions. General-purpose
programming languages are not up to the task.
- Semantic actions *do not* belong in a grammar. They create yet
another programming language to deal with when doing parsing and
translation: the source language, the grammar language, the semantics
language, the generated parser's language, and the translation's
target language. Most grammar parsers do not check the syntax of
embedded semantic actions, so errors get reported at awkward moments,
and against the generated code, not against the grammar.
- Preprocessing (like dealing with includes, fixed column formats, or
structure-through-indentation) belongs in well-designed program code;
not in the grammar.
- It is easy to recruit help with knowledge about a mainstream
programming language like `Python`_, but help is hard to find for
working with complex grammar-description languages. |TatSu|
grammars are in the spirit of a *Translators and Interpreters 101*
course (if something is hard to explain to a college student, it's
probably too complicated, or not well understood).
- Generated parsers should be easy to read and debug by humans. Looking
at the generated source code is sometimes the only way to find
problems in a grammar, the semantic actions, or in the parser
generator itself. It's inconvenient to trust generated code that one
cannot understand.
- `Python`_ is a great language for working with language parsing and
translation.
|
