*          What's cool about CHICKEN 5?
#+STARTUP: inlineimages
                   [[./chicken-logo.png]]


**                   Peter Bex

                    T-DOSE
                   Eindhoven
                May 11th, 2019

* Who am I?

** Peter Bex

*** Work: codeyellow.nl  
  We're hiring! Talk to me or Burhan later
*** Freelancing on the side: pebble-software.nl
*** Blog (mostly about CHICKEN): more-magic.net

*** Fell in love with Scheme at university, ~2002
*** CHICKEN user since 2003
  eggs: postgresql, spiffy, http-client, ...
*** CHICKEN core contributor since late 2009
  regex engine, macros, garbage collector, ...
* Scheme: intro
 Dialect of /LISP/, a functional language (impure)
 LISP is from 1958, Scheme 1975; still here!

 Other Lisps: Common Lisp, Emacs Lisp, Clojure, ..
 Not for everyone -> Love it or hate it!
#+BEGIN_SRC scheme
 (display "Hello, world!\n") ;; Obligatory

 (define (fib n) ;; Fibonacci, because why not
   (if (<= n 2)
       1
       (+ (fib (- n 1))
          (fib (- n 2)))))
#+END_SRC

* Scheme: philosophy

** Super minimal but powerful language
 User is an equal to the makers of the language

 Very few things *need* "special" support

 Advantages of small extensible core:
 - ease of understanding (fits in your head)
 - embeddability
 - facilitates experimental implementations
 - timelessness; e.g. classes can just be a
   library. C => C++/ObjC, Pascal => Object Pascal
   but Scheme => Scheme
* Scheme superpowers: macros

** Fully hygienic macro system
#+BEGIN_SRC scheme
 (define-syntax swap!
   (syntax-rules ()
     ((_ a b) (let ((x a))
                (set! a b)
                (set! b x)))))

 ;; Does the right thing, i.e. print 2:
 (let ((x 1) (y 2))
   (swap! x y)
   (display y))
#+END_SRC

* Scheme superpowers: closures

** Lexical scoping

 Gives us *closures* (now ubiquitous; first LISP)
#+BEGIN_SRC scheme
 (define (make-counter)
   (let ((val 0))
     (lambda () ; Anonymous fn, closes over "val"
       (set! val (+ val 1))
       val)))
 (define c (make-counter))
 (c) ; 1
 (c) ; 2
#+END_SRC

* Scheme superpowers: continuations

** Continuations

 Can be used to implement exceptions, co-routines,
 serialize full program state, etc etc

 Tail calls "for free" [Lambda the Ultimate Goto]
 Tail recursion is /required by the spec/!
 Bad implementations often conveniently ignore it

 Deep recursion is okay; just eats up more heap

 See also Stackless Python

* Scheme superpowers: numeric tower

** Numeric tower

Systematic support for /all the numbers/
Spec defines system, subset is allowed (see later)
#+BEGIN_SRC scheme
1           ;; exact integer
0.5         ;; inexact real number
1/2         ;; exact rational number
1+2i        ;; exact complex number
0.5+0.25i   ;; inexact complex number
1/2+3/4i    ;; ALSO an exact complex number
(+ 3/4 1/2) ;; yes, this returns 5/4
#+END_SRC

* Scheme superpowers: REPL

** Read-Eval-Print-Loop

*** Interpreter prompt allows you to explore

  Type an expression  (read)
  Have it evaluated   (eval)
  See the result      (print)
  Go to start         (loop)

  Most interpreters do this now.
  Done right, can shape your way of thinking.
  LISP machines did it best! (SLIME/Geiser)

* CHICKEN: intro

 /Implementation/ of Scheme (one of the few
 serious ones)

 Based on Henry Baker's [Cheney On The MTA] idea:
 Use C stack for initial heap (nursery)

 Been around since 2000.

 Compiles to C.  Uses GCC, clang, ... to generate
 machine code, so: very portable

 *Great* community! Produced lots of libraries

* CHICKEN: C interop

 Interop with C is trivial; just drop down to it
#+BEGIN_SRC scheme
 (import (chicken foreign))

 (foreign-declare "#include <math.h>")

 (define twice-exp
   (foreign-lambda* double ((double x))
     "double result = exp(x);"
     "C_return(result * 2.0);"))

 (display (twice-exp 5)) ;; 296.826318205153
#+END_SRC

* CHICKEN 5: Overhaul of module system

** Most user-visible change
 Old CHICKENs had such memorable module names as
 "utils" and "extras"... Most was in "chicken"

 Hard to remember, inconsistent

 Large libraries (but few imports needed)

** Naming scheme (haha) inspired by R7RS
 (scheme base) => (chicken base)
 (scheme file) => (chicken file) etc
 others: (chicken posix), (chicken foreign) etc
* CHICKEN 5: Overhaul of module system; examples

** A few good examples to give you an idea:
 "sort" procedure in CHICKEN 4: data-structures
 "sort" procedure in CHICKEN 5: (chicken sort)

 "symbol-append" in CHICKEN 4: library?! chicken
 "symbol-append" in CHICKEN 5: (chicken base)

 "->string" in CHICKEN 4: data-structures
 "->string" in CHICKEN 5: (chicken string)

 "read-line" in CHICKEN 4: extras
 "read-line" in CHICKEN 5: (chicken io)

* CHICKEN 5: Numeric tower; old situation

** Older CHICKENs had only "fixnums" and "flonums"

*** Quite fast (compile to ~standard C float/int)

*** Never felt very "complete" or "serious" to me
 LISP/Scheme is awesome, dammit!

*** Issues with C FFI
 Only 62 (or 30) bits available for ints; 
 precision loss

** So, I made it my mission to fix this

* CHICKEN 5: Numeric tower; new situation

** Most important: large integers ("bignums")
 C FFI finally supports /size_t/ and friends!

** Exact rational numbers are nice too;
 Calculations will always be exact

** Complex numbers mostly for completeness
 Not that many use-cases(?)

** Pretty fast, but a bit slower than CHICKEN 4
 Mostly due to pre-allocation.  Working on it!
*** Enough self-promotion, on to other features
* CHICKEN 5: static compilation

** Great for binary deployment / distribution
 No need to mess around with "virtualenvs" etc

 Just plop the binary onto a server; done

 Killer feature of Go, for example

** CHICKEN always supported static compilation!
 Sucked for eggs (nobody tests it)

** Solution: declarative egg format
 Makes it harder to mess up
* CHICKEN 5: static compilation; old situation

** Old (imperative) .setup-file format:
#+BEGIN_SRC scheme
 (compile -s ncurses.scm -L -lncurses -j ncurses)
 (compile -s ncurses.import.scm)
 (compile -c ncurses.scm -L -lncurses 
          -unit ncurses) ; Almost nobody did this

 (install-extension
  'ncurses
  '("ncurses.o" "ncurses.so" "ncurses.import.so")
  '((version "1.6")
    (static "ncurses.o"))) ; And this
#+END_SRC scheme

* CHICKEN 5: static compilation; new situation

** New (declarative) .egg-file format:
#+BEGIN_SRC scheme
 ((synopsis "An interface to ncurses")
  (category ui)
  (license "BSD")
  (build-dependencies bind)
  (author "felix winkelmann")
  (maintainer "The CHICKEN Team")
  ;; This replaces the .setup file:
  (components (extension ncurses
                (link-options -L -lncurses))))
#+END_SRC scheme

* CHICKEN 5: declarative egg files; sh scripts

** Generates sh scripts (batch files on Windows)
#+BEGIN_SRC sh
 chicken-do ncurses.so ncurses.import.scm : \
  ncurses.scm ncurses.egg : \
  csc -host -J -s -setup-mode -I . -C -I. \
  -L -lncurses ncurses.scm -o ncurses.so

 chicken-do ncurses.static.o ncurses.link : \
  ncurses.scm ncurses.egg : \
  csc -setup-mode -static -I . -emit-link-file \
  ncurses.link -host -c -unit ncurses \
  -C -I. ncurses.scm -o ncurses.static.o
#+END_SRC

* CHICKEN 5: declarative egg files; advantages

** Advantages of declarative format

 Static linking is *always* built-in

 Cross-compilation is made easier

 Support for new features can be retroactively
 added to all eggs

 Security

 Less typing!

* CHICKEN 5: binary reproducible builds

** Both CHICKEN itself and eggs

 Made output of Scheme to C conversion stable
 C to binary is left to the C tool chain

** Gives us verifiability

 See also [reproducible-builds.org]

** Nice bonus: Faster builds with ccache

 Generated C is identical!

* Final words

** Most important eggs have already been ported!
 CHICKEN 5 is recommended for new code

** Start porting your CHICKEN 4 code
 How-to guide: wiki.call-cc.org/porting-c4-to-c5

** CHICKEN 5.1 is upcoming
*** Bugfixes, perf improvements, cleanups
 The usual

*** New "c-objects" declaration in egg files
 Some eggs will require 5.1!

* Thank you!
                    [[./chicken-logo.png]]

**                 CHICKEN website
                   call-cc.org

**                   IRC channel
              #chicken on Freenode

**                     My blog
                 more-magic.net