BETA: A small fast lisp interpeter for a ESP8266 as alternative to lua on the nodemcu.
Who doesn't need a lisp? I always wanted my own "lispmachine" anyway ;) It's ideally small and interactive for experimentation, very little typing, compared to lua for example, easy to extend with FFI to add new functions.
what is lisp?
Lisp is syntactically a very simple language. It has in principle just function calls:
lisp> (+ 3 4) => 7
- embedded small lisp - OK
- memory efficient - OK
- full closures ala scheme - DONE
- tail recursion to allow for actors/coroutines - "OK"
- interactive development instead of compile/upload/run - OK
- readline or better terminal interface - DONE
- easy to add functions by registering, good FFI - DONE
- no macros use NLAMBDA concept instead - "OK"
You can learn some about this lisp internals in my talk and the discussion at Hackware: Holiday 2015 Special, which took place in Singapore end of last year.
The core is about 1000 lines of code. Total around 4000 with extentions functions and xml/web server support.
The esp-lisp has been used to build some smaller game devices by other persons, still things being added.
- small (~ n*1000 lines of code)
- full scheme style closures (make your own objects)
- lisp reader/printer
- datatypes: string, atom, int, cons, prim, thunk, immediate, func
- simple mark/sweep GC
- efficient storage of conses, with no overhead per cell, no tag word needed
- inline (no overhead at all!) small ints, short symbols (<=6 chars) stored INSIDE POINTER!
- tail recursion optimization using "immediate" thunks, handles mutual/self recursion
- eval/neval LAMBDA/NLAMBDA primitive functions, no need for macros, no code explosion reddit
- readline, with limited editing (backspace), similar to nodemcu lua
- full screen editor function, like emacs implemented in ~500 lines single file imacs.
- in/out/dht functions
- interrupt (counting) api and callback functions
The esp-lisp is interpreted, to keep the code small and simple. Compared to lua from the NodeMCU it's about 2x slower, but lua is compiled and uses lots of memory for functions. Lua uses about 600 bytes for a simple function, whereas esp-lisp about 100 bytes for a function printing hello.
Comparing it to guile by running (fib 33) takes about 10s on guile, but only 5s on esp-lisp!
advanced terminal interaction
In the read-eval loop:
- CTRL-C will terminate input and start over on new line
- CTRL-H/DEL will delete last character
- CTRL-L will reprint line cleanly
- CTRL-T print current status time/load
Full screen emacs-style editing
Uses the imacs minimal editor implementation as a sub-project.
lisp> (define txt "foobar") lisp> (set! txt (edit txt)) ... edit in fullscreen! ... (+ 3 4) ctrl-x ctrl-e ==> 7
- CTRL-T print current status time/load and a compressed stack (names of functions only)
- CTRL-C will "break" the code and print the stack, cleanup and go to top-level
- 'kill -20 ' in another will clear screen and print the current stack
- 'watch -n 0 kill -20 '' will continously print the stack; try it on '(fibo 90)' - quite facinating!
how to build
In the example below I "assume" you have a directory GIT where you checkout all your projects.
I want to run it on my linux/cygwin, I have GCC
- unix:GIT> git clone http://github.com/yesco/esp-lisp.git --recursive
- unix:GIT> cd esp-lisp
- unix:GIT/esp-lisp> ./run
It'll compile and run it for you, you'll have a lisp prompt.
lisp> help ...
try out the commands, it also shows what functions/symbols there are
lisp> (+ 3 4) 7 lisp> (setq fac (lambda (n) (if (= n 0) 1 (* n (fac (- n 1)))))) #func lisp> (fac 6) 720
build embeddable image and flash it to a nodemcu/EPS8266 device
In a directory:
Get https://github.com/SuperHouse/esp-open-rtos (and all it wants)
These will now be in the same directory.
Create a file path-add-esp (one level up from esp-lisp). It should contain something like:
unix:GIT> cat path-add-esp export PATH=/home/USER/...GIT/esp-open-sdk/xtensa-lx106-elf/bin:$PATH unix:GIT> source path-add-esp
- unix:esp-lisp> ./run
That will compile and run it on your desktop.
- unix:esp-lisp> make flash
Flashes it to your esp-8266 device.
- unix:esp-lisp> ./mcu
To connect to it and run it. Requires screen.
- integers stored free inside the pointer (only 32-3-29 bits) - DONE (increased speed 30%!)
- a-z up to 6 letter symbol names stored for free inside pointer - DONE (saved 1600 bytes!)
- 3 ascii symbol names stored for free inside pointer - DONE
- global bindings stored in a hashed "symbol table" - DONE (increase speed 15%, saved 150 cons! ~ 1KB)
- primtive functions are global and stored inside the global binding (4 bytes overhead) - DONE (saved 600 bytes!)
- long name/non-alpha symbols allocated in global symbol table using "hash pointer" (for use in flash!)
- cons stored in preallocated chunk with one bit overhead per cons, size about 5K - DONE (saved 8 bytes per cons)
- regression tests - in progress
- more tests - working on it
- simple web server interface (ala http://john.freml.in/teepeedee2-vs-picolisp) - DONE
- speed regression test suite (tail recursion and http://software-lab.de/radical.pdf)
- add functionality ala nodemcu see http://www.nodemcu.com/docs/
- want nodemcu spiffs style filesystem on flash - depends on esp-open-rtos/issue
- hardware io functions: spi i2c
- put lisp functions in ROM at compile time, see below for inspiriation - in progress
- get lcd/tft display functions ala nodemcu
- make a stand-alone lisp machine, that can take PC2 keyboard and a 240x160 color display
Readings idea for embedded ROM lisps
Optimize more for storage/simplify and avoid using malloc here are some ideas from elsewhere.
- picolisp speed tests... http://software-lab.de/radical.pdf
- picolisp puts compiled lisp in ROM - http://picolisp.com/wiki/!pdf?-B1054
Flash based filesystems or flash database log systems
- http://research.microsoft.com/en-us/um/people/moscitho/Publications/USENIX_ATC_2015.pdf (normal filesystem that concentrate on checkpointing/logging, for staleness and power usage)