Introduction How not to design a scripting language How not to Design a Scripting Language Paul Biggar Department of Computer Science and Statistics Trinity College Dublin StackOverflow London, 28th October, 2009 How not to Design a Scripting Language Paul Biggar PhD Dissertation Design and Implementation of an Ahead-of-time PHP Compiler phc (http://phpcompiler.org) Introduction How not to design a scripting language About me • PhD candidate, Trinity College Dublin • Topic: Compilers, optimizations, scripting languages. How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language About me • PhD candidate, Trinity College Dublin • Topic: Compilers, optimizations, scripting languages. PhD Dissertation Design and Implementation of an Ahead-of-time PHP Compiler phc (http://phpcompiler.org) How not to Design a Scripting Language Paul Biggar • Speed Introduction How not to design a scripting language How not to design a scripting language • Compilers • Scripting Languages How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language How not to design a scripting language • Compilers • Scripting Languages • Speed How not to Design a Scripting Language Paul Biggar Common Features: • Dynamic typing • Duck typing • Interpreted by default • FFI via C API Introduction How not to design a scripting language What is a scripting language? • Javascript • Lua • Perl • PHP • Python • Ruby How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language What is a scripting language? • Javascript • Lua • Perl • PHP • Python • Ruby Common Features: • Dynamic typing • Duck typing • Interpreted by default • FFI via C API How not to Design a Scripting Language Paul Biggar NOT THE DRAGON BOOK Engineering a Compiler by Cooper/Torczon Modern Compiler Implementation in X by Appel • Compilers: Not too hard, sometimes portable, optimizations • Just-in-time compilers: Very difficult, unportable, fast interpreter. Introduction How not to design a scripting language Language implementation • Interpreters: Easy, portable How not to Design a Scripting Language Paul Biggar • Just-in-time compilers: Very difficult, unportable, fast NOTinterpreter THE DRAGON. BOOK Engineering a Compiler by Cooper/Torczon Modern Compiler Implementation in X by Appel Introduction How not to design a scripting language Language implementation • Interpreters: Easy, portable • Compilers: Not too hard, sometimes portable, optimizations How not to Design a Scripting Language Paul Biggar • Just-in-time compilers: Very difficult, unportable, fast interpreter. Introduction How not to design a scripting language Language implementation • Interpreters: Easy, portable • Compilers: Not too hard, sometimes portable, optimizations NOT THE DRAGON BOOK Engineering a Compiler by Cooper/Torczon Modern Compiler Implementation in X by Appel How not to Design a Scripting Language Paul Biggar NOT THE DRAGON BOOK Engineering a Compiler by Cooper/Torczon Modern Compiler Implementation in X by Appel Introduction How not to design a scripting language Language implementation • Interpreters: Easy, portable • Compilers: Not too hard, sometimes portable, optimizations • Just-in-time compilers: Very difficult, unportable, fast interpreter. How not to Design a Scripting Language Paul Biggar 1 Elegant and well designed, 2 High level of abstraction, 3 Dynamic typing (and duck typing). Introduction How not to design a scripting language What’s right with scripting languages? How not to Design a Scripting Language Paul Biggar 2 High level of abstraction, 3 Dynamic typing (and duck typing). Introduction How not to design a scripting language What’s right with scripting languages? 1 Elegant and well designed, How not to Design a Scripting Language Paul Biggar 3 Dynamic typing (and duck typing). Introduction How not to design a scripting language What’s right with scripting languages? 1 Elegant and well designed, 2 High level of abstraction, How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language What’s right with scripting languages? 1 Elegant and well designed, 2 High level of abstraction, 3 Dynamic typing (and duck typing). How not to Design a Scripting Language Paul Biggar Problem: Language designed for one interpreters specific interpreter • Run-time source code execution • Foreign Function Interface Introduction How not to design a scripting language What’s wrong with scripting languages? Symptoms: Speed, Portability How not to Design a Scripting Language Paul Biggar Problem: Language designed for one specific interpreter • Foreign Function Interface Introduction How not to design a scripting language What’s wrong with scripting languages? Symptoms: Speed, Portability Problem: Language designed for interpreters • Run-time source code execution How not to Design a Scripting Language Paul Biggar Problem: Language designed for interpreters Introduction How not to design a scripting language What’s wrong with scripting languages? Symptoms: Speed, Portability Problem: Language designed for one specific interpreter • Run-time source code execution • Foreign Function Interface How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language FFI FFI Foreign Function Interface based on CPython interpreter • Access to C libraries • Script C applications using Python scripts • Rewrite hot code in C How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language FFI FFI (good) implications • Libraries not that slow • Can break out of Python for slow code. How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language FFI FFI (bad) implications • Language is allowed to be slow • Must break out of Python for speed. How not to Design a Scripting Language Paul Biggar • Reimplementations Introduction How not to design a scripting language FFI FFI (worse) implications • Legacy issues How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language FFI FFI (worse) implications • Legacy issues • Reimplementations How not to Design a Scripting Language Paul Biggar • Only one way of FFI is better • Declarative is best • Any reimplementation can reuse the same libraries without any modifications • CPython itself can change without hassle Introduction How not to design a scripting language FFI FFI solution Don’t expose yourself! • Importing functions into Python with a Domain Specific Language is good How not to Design a Scripting Language Paul Biggar • Declarative is best • Any reimplementation can reuse the same libraries without any modifications • CPython itself can change without hassle Introduction How not to design a scripting language FFI FFI solution Don’t expose yourself! • Importing functions into Python with a Domain Specific Language is good • Only one way of FFI is better How not to Design a Scripting Language Paul Biggar • Any reimplementation can reuse the same libraries without any modifications • CPython itself can change without hassle Introduction How not to design a scripting language FFI FFI solution Don’t expose yourself! • Importing functions into Python with a Domain Specific Language is good • Only one way of FFI is better • Declarative is best How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language FFI FFI solution Don’t expose yourself! • Importing functions into Python with a Domain Specific Language is good • Only one way of FFI is better • Declarative is best • Any reimplementation can reuse the same libraries without any modifications • CPython itself can change without hassle How not to Design a Scripting Language Paul Biggar eval (mysql_read (...)[0]); username="myname" $langpassword= ....="mypass; " includeserver="(srv.domain.com"localisation/locale." $lang.php"); • meta-programming • .rc files • localization Introduction How not to design a scripting language Compiled and interpreted models Dynamic source code generation • eval and dynamic include/import How not to Design a Scripting Language Paul Biggar username="myname" $langpassword= ....="mypass; " includeserver="(srv.domain.com"localisation/locale." $lang.php"); • .rc files • localization Introduction How not to design a scripting language Compiled and interpreted models Dynamic source code generation • eval and dynamic include/import • meta-programming eval (mysql_read (...)[0]); How not to Design a Scripting Language Paul Biggar $lang= ....; include ("localisation/locale.$lang.php"); eval (mysql_read (...)[0]); • localization Introduction How not to design a scripting language Compiled and interpreted models Dynamic source code generation • eval and dynamic include/import • meta-programming • .rc files username="myname" password="mypass" server="srv.domain.com" How not to Design a Scripting Language Paul Biggar eval (mysql_read (...)[0]); username="myname" password="mypass" server="srv.domain.com" Introduction How not to design a scripting language Compiled and interpreted models Dynamic source code generation • eval and dynamic include/import • meta-programming • .rc files • localization $lang= ....; include ("localisation/locale.$lang.php"); How not to Design a Scripting Language Paul Biggar Introduction How not to design a scripting language Compiled and interpreted models Dynamic source code generation We don’t even know the full program source!! How not to Design a Scripting Language Paul