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Providing Rapid Feedback in Generated Modular Language Environments Lennart Kats ( me ) Maartje de Jonge Emma Nilsson-Nyman Eelco Visser OOPSLA 2009 October 29, 2009 Software Engineering Research Group

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Providing Rapid Feedback in Generated Modular Language Environments

Lennart Kats (me) Maartje de Jonge Emma Nilsson-Nyman Eelco Visser

Software Engineering Research Group

OOPSLA 2009 October 29, 2009

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Domain-Specific Languages

  • Encapsulate domain knowledge
  • Eliminate boilerplate code
  • Domain-specific analysis / verification /
  • ptimization
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UI Data models

Integration and Composition of DSLs

HQL Workflow Access control Data validation Actions

(www.webdsl.org)

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Markus Voelter [Practical Product Lines 2009] DSLs without IDE support are a nonstarter!

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Spoofax/IMP: Efficient Editor Development

  • Existing platform: Eclipse with IMP
  • DSLs to define editor components
  • Grammar and a parser generator:

SDF, (J)SGLR

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Code Folding Semantic errors Outline References HQL Brace matching

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FOLDING/OUTLINE entity User { ... } entity BlogPost { poster : User body : String } REFERENCE

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entity User { name : String password : String homepage } entity BlogPost { poster : User body : String }

What about incorrect and incomplete programs?

NORMAL PARSING }

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entity User { name : String password : String homepage } entity BlogPost { poster : User body : String }

What about incorrect and incomplete programs?

NORMAL PARSING ERROR NEVER PARSED Parse failure: No abstract syntax tree

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Mini-Demo

Error Recovery in a data modeling language

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Parsing with SDF and SGLR

  • Language composition without

shift/reduce conflicts

  • Ambiguities can be inspected
  • Declarative disambiguation
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token token token token token token token token token token token

x x x

token

x

Recovery: Backtracking, skip/insert tokens, etc.

Normal LR Parser (S)GLR Parser

Recovery: ?

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Do we really need to dive into this intimidating algorithm?

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Island Grammars

IDENTIFICATION DIVISION. PROGRAM-ID. EXAMPLE. PROCEDURE DIVISION. CALL X. YADA. YADA YADA. CALL Y. CALL X. CALL Y. WATER WATER

  • Parse only interesting bits (Islands)
  • Skip the remaining characters (Water)

[Van Deursen & Kuipers, 1999] Grammar-based “error recovery”!

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Island Grammars

~[\ \t\n]+ → WATER {avoid} [Van Deursen & Kuipers, 1999]

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Running Example: Java

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  • 1. Take the entire Java grammar
  • 2. Add water
  • 3. Mix it together

Error Recovery Recipe

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } ERROR

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } NORMAL PARSING ERROR

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } } NORMAL PARSING ERROR

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } } NORMAL PARSING ERROR UNEXPECTED KEYWORD

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } New production: WATER → MethodDec {cons(“WATER”)} New production: WATER → MethodDec {cons(“WATER”),recover}

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New production: WATER → MethodDec {cons(“WATER”),recover} New production: WATER → Stm {cons(“WATER”),recover}

Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } WATER

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } New production: WATER → Stm {cons(“WATER”),recover} WATER

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } WATER LAYOUT PROBLEMATIC TOKEN

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } New production: WATER → LAYOUT {cons(“WATER”),recover} WATER LAYOUT PROBLEMATIC TOKEN

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Mixing Java with Water

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } WATER New production: WATER → LAYOUT {cons(“WATER”),recover} LAYOUT

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Reflection: Water-based Recovery Rules

  • Works with any existing grammar
  • Can only remove fragments
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Danger of Floods

public class Fridge { public void startCooling() { cooling.commence(); // missing } public void onResetButtonPress() { log.message(“Reset button pressed”); power.reboot(); } }

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Danger of Floods

public class Fridge { public void startCooling() { cooling.commence(); // missing } public void onResetButtonPress() { log.message(“Reset button pressed”); power.reboot(); } } WATER So why not parse methods with missing closing brackets?

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“if” “(” Expr Stm → Stm {cons(“If”), recover}

Productions for Missing Literals

“if” Expr “)” Stm → Stm {cons(“If”), recover} “if” Expr Stm → Stm {cons(“If”), recover} “while” “(“ Expr Stm → Stm {cons(“While”), ...} ... and this, and this, and this: why not add rules like this: not going to scale.

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IF BOPEN … BCLOSE … → … [\i][\f] → IF [\(] → BOPEN [\)] → BCLOSE

Productions for Missing Literals

→ BCLOSE {recover} → “}” {recover} “)” so, we can write (using the literal instead of BCLOSE): what it means internally: “if” “(” Expr “)” Stm → Stm {cons(“If”)}

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Applying Insertion Rules

public class Fridge { public void startCooling() { cooling.commence(); // missing } public void onResetButtonPress() { log.message(“Reset button pressed”); power.reboot(); } } New production: → “}” {recover}

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Applying Insertion Rules

public class Fridge { public void startCooling() { cooling.commence(); // missing } public void onResetButtonPress() { log.message(“Reset button pressed”); power.reboot(); } } INSERT } New production: → “}” {recover}

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So who's gonna write all those recovery rules?

  • Water
  • Closing brackets (“}”)
  • Opening brackets (“{”)
  • Separators (“,”)
  • Comments
  • String literals

Recovery Rules

We derive them from the grammar!

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Customization of Recovery Rules

→ “class” {reject} “[|” → “|[“ {recover} “|]” → “]|” {recover}

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Putting Things Together

y = f ( x + 1 ; y = f ( x + 1 ) ; y = f ( x ) + 1 ; y = f + 1 ; y = f ( 1 ) ; y = ( x ) + 1 ; y = ( x + 1 ) ; y = x + 1 ; y = f ; y = ( x ) ; y = f ( ) ;

  • Water
  • Insertion: “)”

y = x ; f ( x + 1 ) ; f ( 1 ) ; y ( x + 1 ) ; y ( x ) ; y () ; y ( 1 ) ; y = 1 ; ;

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Putting Things Together

For recovery, parallel parsing does not scale...

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Putting Things Together

Why not do backtracking for recovery?

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Recovery Using Backtracking

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } ERROR

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Recovery Using Backtracking

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } }

  • 1. NORMAL PARSING

ERROR

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Recovery Using Backtracking

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } }

  • 1. NORMAL PARSING

ERROR POINT OF DETECTION

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Recovery Using Backtracking

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } }

  • 2. BACKTRACKING
  • 1. NORMAL PARSING
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Recovery Using Backtracking

public class TemperatureMonitor { private Fridge fridge; public void trigger(Temperature temp) { if (temp.greaterThan(MAX)) // missing { fridge.startCooling(); } return; } public TemperatureMonitor(Fridge fridge) { this.fridge = fridge; } } 1 RULE 1 RULE 2 RULES 1 RULE 2 RULES 3 RULES 1 RULE 2 RULES 3 RULES 4 RULES {

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Evaluation

Implementation:

  • JSGLR
  • Spoofax/IMP (WebDSL, Stratego, PIL, ...)

Test grammars:

  • Java
  • Java-SQL
  • Stratego
  • Stratego-Java
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Evaluation

Measurements:

  • qualitative [Penello & DeRemer '78]:

excellent / good / poor

  • tree alignment distance [Jian et al '94]
  • textual 'diffs'
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Recovery Quality (Stratego-Java)

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Continued Work

“Natural and Flexible Error Recovery for Generated Parsers” [SLE 2009]

  • indentation-based region selection
  • fall-back mechanism
  • bridge parsing [Nilsson-Nyman et al, 2008]

(www.strategoxt.org/Stratego/PermissiveGrammars)

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Continued Work

“Natural and Flexible Error Recovery for Generated Parsers” [SLE 2009]

  • comparison with JDT
  • performance, quality
  • synergy between recovery techniques

(www.strategoxt.org/Stratego/PermissiveGrammars)

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www.strategoxt.org/Stratego/PermissiveGrammars www.strategoxt.org/Stratego/Spoofax-IMP www.lennartkats.net

Software Engineering Research Group

Conclusion

SGLR/SDF

  • modular specifications
  • composable languages

Recovery production rules

  • transparent
  • flexible
  • language-independent