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RefactoringErlang Programs
Huiqing LiSimon Thompson University of
Kent
Zoltán Horváth
Eötvös Loránd Univ.
EUC 2006
Overview
Example refactoringsGeneral observationsChallenges of ErlangOur two implementationsNext steps … and conclusion
EUC 2006
Soft-ware
There’s no single correct design …
… different options for different situations.
Maintain flexibility as the system evolves.
EUC 2006
Generalisation
-module (test).-export([f/1]). add_one ([H|T]) -> [H+1 | add_one(T)];
add_one ([]) -> [].
f(X) -> add_one(X).
-module (test).-export([f/1]). add_one (N, [H|T]) -> [H+N | add_one(N,T)];
add_one (N,[]) -> [].
f(X) -> add_one(1, X).
-module (test).-export([f/1]). add_int (N, [H|T]) -> [H+N | add_int(N,T)];
add_int (N,[]) -> [].
f(X) -> add_int(1, X).
Generalisation and renaming
EUC 2006
Generalisation
-export([printList/1]).
printList([H|T]) -> io:format("~p\n",[H]), printList(T);printList([]) -> true.
printList([1,2,3])
-export([printList/2]).
printList(F,[H|T]) -> F(H), printList(F, T);printList(F,[]) -> true.
printList( fun(H) -> io:format("~p\n", [H]) end, [1,2,3]).
EUC 2006
Generalisation
-export([printList/1]).
printList([H|T]) -> io:format("~p\n",[H]), printList(T);printList([]) -> true.
-export([printList/1]).
printList(F,[H|T]) -> F(H), printList(F, T);printList(F,[]) -> true.
printList(L) -> printList( fun(H) -> io:format("~p\n", [H]) end, L).
EUC 2006
Asynchronous to synchronous
pid! {self(),msg}
{Parent,msg} -> body
pid! {self(),msg}, receive {pid, ok}-> ok
{Parent,msg} -> Parent! {self(),ok}, body
EUC 2006
Refactoring = Transformation + Condition
Transformation
Ensure change at all those points needed.
Ensure change at only those points needed.
Condition
Is the refactoring applicable?
Will it preserve the semantics of the module? the program?
EUC 2006
Transformations
full stop one
EUC 2006
Condition > TransformationRenaming an identifier"The existing binding structure should not be affected. No binding for the new name may intervene between the binding of the old name and any of its uses, since the renamed identifier would be captured by the renaming. Conversely, the binding to be renamed must not intervene between bindings and uses of the new name."
EUC 2006
Tool support
Bureaucratic and diffuse.
Tedious and error prone.
Semantics: scopes, types, modules, …
Undo/redo
Enhanced creativity
EUC 2006
Static vs dynamic
Aim to check conditions statically.
Static analysis tools possible … but some aspects intractable: e.g. dynamically manufactured atoms.
Conservative vs liberal.
Compensation?
EUC 2006
Compensate or fail?
-export([oldFun/1, newFun/1]).
oldFun(L) -> newFun(L).
newFun(L) -> … … .
-export([newFun/1]).
newFun(L) -> … … .
or ?
EUC 2006
Erlang refactoring: challenges Multiple binding occurrences of variables.Indirect function call or function spawn: apply (lists, rev, [[a,b,c]]) Multiple arities … multiple functions: rev/1
ConcurrencyRefactoring within a design library: OTP.Side-effects.
EUC 2006
Haskell vs Erlang refactorings
Haskell Refactorings Erlang Refactorings
Type/type class-related refactorings.Monad-related refactorings. . . . . .
Introduce/remove concurrency,Asynchronous/synchronous
communication,Refactoring to design patterns, . . . . . .
Renaming,Removing unused definitions/parameters,Swapping arguments,Introduce new definitions, . . . . . .
EUC 2006
Architectures
EUC 2006
Wrangler in Emacs
EUC 2006
Wrangler in Emacs
EUC 2006
AST vs database
Lightweight.
Better integration with interactive tools (e.g. emacs).
Undo/redo external?
Ease of implementing conditions?
Higher entry cost.
Better for a series of refactorings on a large project.
Transaction support.
Ease of implementing transformations?
EUC 2006
Next steps
Refactor concurrency
• styles• introduction
Refactor Erlang/OTP
• within OTP• towards OTP
Release systems by the end of January.
Performance comparisons on real systems.
EUC 2006
Ackonwledgements
EPSRC
ELTE IKKK, CNL
Ericsson Hungary
Bolyai Res Fellowship
syntax-tools
distel
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