The document describes the development of a new Epsilon language called the Epsilon Demo Language (EDL) which extends the Epsilon Object Language (EOL) with the concept of "process rules". Process rules allow code to be executed for every instance of a model element. The execution engine and Eclipse-based development tools for EDL were implemented with only a few hundred lines of code by heavily reusing and extending existing EOL components.

1. Developing a new Epsilon Language
through Grammar Extension:
The Epsilon Demo Language (EDL)
Dimitris Kolovos
@kolovos
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2. Epsilon Demo Language
• A new language that extends EOL and introduces
the concept of a "process rule"
• Process rules are simple rules that are executed
for every instance of their parameter
// This will be run for every
// instance of EClass
process c : EClass {
// Here we can run arbitrary EOL code
c.name.println();
}
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3. AnnotaLons vs. Grammar Extension
• No hard rule
• AnnotaLons
– Language closer to EOL
• Grammar extension
– New syntacLc constructs with no clear mapping to
EOL
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4. Overview
• Two Eclipse plugins
– One for the language's execuLon engine
• org.eclipse.epsilon.edl.engine
• Can run outside Eclipse
– One for the language's Eclipse-based
development tools
• org.eclipse.epsilon.edl.dt
• Source code available under
hTps://git.eclipse.org/c/epsilon/
org.eclipse.epsilon.git/tree/examples
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5. EDL'S EXECUTION ENGINE
org.eclipse.epsilon.edl.engine
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7. grammar Edl;
options {backtrack=true; output=AST;
ASTLabelType='org.eclipse.epsilon.common.parse.AST';
superClass='org.eclipse.epsilon.common.parse.EpsilonParser';}
import EolLexerRules, EolParserRules;
tokens { EDLMODULE; PROCESS; }
@header { package org.eclipse.epsilon.edl.parse; }
@lexer::header { package org.eclipse.epsilon.edl.parse; }
edlModule : importStatement* (edlModuleContent)* EOF
-> ^(EDLMODULE importStatement* edlModuleContent*);
edlModuleContent : processRule | operationDeclaration ;
processRule : r='process'^ formalParameter statementBlock
{$r.setType(PROCESS);} ;
ANTLR Grammar: Edl.g
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8. EdlModule.java
• InstanLates the generated parser
• Obtains a homogeneous concrete syntax tree
(CST) from the generated EDL parser
• Transforms the CST into an abstract syntax tree
(AST)
– AST contains instances of ProcessRule, IfStatement,
WhileStatement etc.
• Executes the AST
• Heavily reuses EolLibraryModule
– 70 lines of code (excluding imports and header)
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9. ProcessRule.java
• Abstract syntax element for EDL's process
rules
• Can populate itself from a process rule CST
• Can execute itself
• Heavily reuses EOL
– 40 lines of code (excluding imports and header)
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10. EDL's ExecuLon Engine
• ~15 lines of ANTLR grammar
• < 200 lines of Java code
– < 100 non-empty lines (excluding imports and
header)
– Much of the code is seTers and geTers
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11. EDL'S ECLIPSE-BASED
DEVELOPMENT TOOLS
org.eclipse.epsilon.edl.dt
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12. Overview
• Three faciliLes
– New EDL file wizard
• NewEdlFileWizard: Trivial (15 lines of code)
– Editor
• Syntax highlighLng, outline view etc.
– Launching faciliLes
• Standard Eclipse run configuraLon, debugger
• Heavily reuse EOL's respecLve faciliLes
– 364 lines of code in total
– 168 lines excluding headers and imports
– + 49 lines of XML for the plumbing (plugin.xml)
• Compared to the annotaLon-based approach we need to also
develop (largely by extending EOL's)
– an editor
– a debugger
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13. EDL EDITOR
87 lines of code
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16. LAUNCHING FACILITIES
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19. EDL's Development Tools
Class LoC Exc. Imports/Headers
EdlModuleContentProvider 37 26
EdlModuleElementLabelProvider 38 18
EdlEditor 59 33
EdlEditorStaLcTemplateContributor 29 10
EdlSourceConfiguraLonTab 48 31
EdlDebugger 28 11
EdlLaunchConfiguraLonDelegate 30 12
EdlLaunchConfiguraLonTabGroup 24 7
NewEdlFileWizard 32 15
EdlPlugin 21 5
Total 346 168
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20. Summary
• <300 lines of code for a new model
management language with custom syntax
– … and its development tools
• Not bad at all 😎
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