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Notes on Oil's Architecture
This doc is for contributors or users who want to understand the Oil codebase.
These internal details are subject to change.
- Essential: libc
- Optional: GNU readline (TODO: other line editing libraries).
- Only in the OVM build (as of March 2020): yajl
- ASDL front end from CPython (heavily
- frontend/tdop.py: Adapted from tinypy, but almost no original code
- All of OPy (will be obsolete)
- compiler2 from stdlib
- Build Dependency: MyPy
Metaprogramming / Generated Code
ls */*_def.py */*_gen.py
def.py files are abstract definitions. They're not translated by
gen.py files generate source code in Python and C++ from these
- For example, we define the core
Id type and the lexing rules abstractly.
- TODO: Details on each
- See build/dev.sh and build/codegen.sh
Other Cross-Cutting Observations
Where $IFS is Used
- Splitting of unquoted substitutions
- The read builtin
- To split words in
compgen -W (bash only)
Shell Function Callbacks
- Completion hooks registered by
complete -F ls_complete_func ls
- bash has a
command_not_found hook; OSH doesn't yet
Where Unicode is Respected
See the doc on Unicode.
Parse-time and Runtime Pairs
echo -e '\x00\n' and
echo $'\x00\n' (OSH shares lexer rules between them)
[[ (OSH shares the parser and evaluator)
- Static vs. Dynamic Assignment.
local x=$y vs.
s='x=$y'; local $s.
- All shells have both notions!
$(( )) (
expr not in shell)
- printf can have a static variant like
find and our own language (although this may be done with blocks)
$IFS splitting in
- compadjust needs to split partial
argv by user-defined delimiters,
The point of a state machine is to make sure all cases are handled!
Generated on Thu May 21 12:33:04 PDT 2020