University of British Columbia

Software Practices Lab

Expressive Programs

Through Presentation

ExtensionAndrew D. Eisenberg

andGregor Kiczales

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 2

Code that Looks Like the Design

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 3

Code that Looks Like the Design

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 4

• Familiar goals, many approaches– Languages

• abstraction level, domain specificity, extensibility…– Editors

• language aware, highlighting, formatting…

• Contributions – New editor/compiler architecture

• synergistic presentation and semantic extensibility• compatible with existing code, tools, practice

– Eclipse-based implementation– Examples

• how light-touch uses of idea can be powerful

Code that Looks Like the Design

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 5

Desirable Properties• Extensibility

– presentation • more than colors, fonts—substantial

difference from concrete syntax• free-form editing

– semantic• like syntax macros

– (abstract syntax graph, not tree)

• Compatibility– with existing code, tools– incremental adoption

• Traceability– of errors– for other tools

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 6

Tool chains

Raw Text (Byte) Code

Other Tools

Display/Edit

Compiler/

Interpreter

Editor

Gnu/Linux

•Language extensibility•code formatting (colors, bold, italics, etc)•text pre-processors

•Communication is line number and character-based

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 7

semantic extensibility

Syntax Macros

AST Expanded AST

Other Tools

Display/Edit

Lisp/Scheme

Raw Text (Byte) Code

•Language extensibility•code formatting•macros

•Communication is line number and character-based

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 8

(Byte) CodeExpanded AST

Structure (Syntax-Directed) Editors

AST

InterlispCornell Program Synthesizer

Other Tools

Display/Edit

Raw Text

•Language extensibility•code formatting•pretty-printing (line breaks, white space, etc)•macros

•Communication between display and byte code can be AST-based

semantic extensibility

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 9

State of the Practice IDEs

•AST easy to create from raw text•cheap, reliable, and fast•incremental•simultaneous maintenance of raw text & AST

•Communication is line-number or AST-based•Restricted extensibility

Eclipse, IntelliJ, Visual Studio, …

Other Tools

AST

Display/Edit

Raw Text (Byte) Code

semantic extensibility

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 10

Raw Text

Display-Driven AST

•AST*—Abstract Syntax Graph•more freedom in displaying code

•Program store is determined by editor•communication is AST-based only•cannot use text-based tools

•Language extensibility•presentation•macros (DrScheme) and AST expansion (Intentional Programming)

DrSchemeIntentional ProgrammingSubtext

Other Tools

Display(AST*)

(Byte) Code

Store

AST

Expanded AST

semantic extensibility

presentation extensibility

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 11

(Byte) CodeExpanded AST

Other Tools

Display/Edit

Raw Text

Presentation Extension of Plain Text

•Language extensibility•presentation•syntactic

•Compatible with modern IDEs•Tool infrastructure•Raw text is accessible

(with syntactic extension)

AST*

semantic extensibility

presentation extensibility

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ExpandedAST

Architecture

Legacy Tools

Display

AST

Byte CodeRaw Text

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ExpandedAST

Architecture

Display

AST

Byte Code

Legacy Tools

Raw Text

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ExpandedAST

Architecture

Display

AST

Byte CodeRaw Text

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Raw Text

ExpandedAST

Architecture

Display

Byte Code

AST

Pair of disjoint, but communicating metaobject protocols

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 16

Implementation

Display

Byte Code

AST

Expanded AST

AST+EditMOs

AST+CompileMOs

Boxes

Controllers

M V

C

Error

Propagation

CTMOP

ETMOP

Pair of disjoint, but communicating metaobject protocols

Raw Text

Edit-Time Metaobject Protocol

Compile-Time Metaobject Protocol

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 17

Traceability

Display

Byte Code

AST

Expanded AST

AST+EMOs

AST+CMOs

Boxes

Controllers

CTMOP

ETMOP

Pair of disjoint, but communicating metaobject protocols

Pair of disjoint, but communicating metaobject protocols

Raw Text

Edit-Time Metaobject Protocol

Compile-Time Metaobject Protocol

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 18

Traceability Allows Error Propagation

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Traceability Allows Code Completion

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• Can be used to create graph edges

• Annotations are familiar

• Annotations work with existing tools

• Valid Java syntax

• Attached to source code

@Getter("get")

@Setter("set")

private int x;

@Previous

private int y;

Metaobjects Serialize to Annotations

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 21

AspectJ Code Style↔Annotation Style

@org.aspectj.lang.annotation.Aspect()

class PointObserving{

@org.aspectj.lang.annotation.After(value="changes(p)")

void advice$aj$0(Point p){

Screen.notify();

}

@org.aspectj.lang.annotation.Pointcut(

"this(p) && execution(void Point.set*(int))")

void changes(Point p){}

}

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 22

Uses

@ca.ubc.cs.etmop.annotations.Uses(

type=BufferedReader.class,

name="file",

init="new BufferedReader(new FileReader(fName))")

public String getFileContents(String fName) {

...

}

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 23

Only presentation extensibility, no semantic

Backquote—Code Generation

return makeMethod( makeModifiers(PUBLIC), makeVoid(), makeName(makeSetterName(varName)), makeParameters( makeParameter(makeType(typeName), makeName(varName))), makeBlock(makeExpressionStatement( makeAssignment(makeFieldAccess( makeThis(), makeName(varName)), makeName(varName)))));

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 24

Equations

public static double mean( final List<Integer> x) {@Equation(Return.DOUBLE)

int MOP_ANNOTATION_HOLDER$0;return Equ.div(

new Summer() { public int body(int i) { return x.get(i); } }.sum(0, x.size() - 1), x.size()); }

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Equation Video

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Stream Processing Automaton

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Presentation Extensions

(Byte) CodeExpanded AST

AST

Other Tools

Display/Edit

Raw Text

RawText

Display

Byte Code

AST

Expanded AST

AST+EMOs

AST+CMOs

Boxes

Controllers

CTMOP

ETMOP

ErrorPropagation

Andrew Eisenberg and Gregor Kiczales — University of British Columbia 28

Questions?

(Byte) CodeExpanded AST

AST

Other Tools

Display/Edit

Raw Text

RawText

Display

Byte Code

AST

Expanded AST

AST+EMOs

AST+CMOs

Boxes

Controllers

CTMOP

ETMOP

ErrorPropagation