Multi-level Debugging for Interpreter Developers at LaMOD'16

Multi-level Debugging for Interpreter Developers

Bastian Kruck, Stefan Lehmann, Christoph Kessler, Jakob Reschke, Tim Felgentreff, Jens Lincke, Robert Hirschfeld

Software Architecture Group, HPI Potsdam15.03.2016, LaMOD16, Málaga

1. Debugging across Languages

2. Debugging within Languages across Abstraction Barriers

3. Unification of such levels

Three Phases

Multi-level Debugging for Intrepreter Developers, LaMOD’16, 15.03.2016, Bastian Kruck Chart 2

How does debugging across languages look like?


How does debugging across languages look like?

Chart 4

Bastian KruckHPI Potsdam


Scheme embedded in Qoppa

Chart 5

Scheme

Qoppa

Embedded in(define if (vau (b t f) env (eval env (bool (eval env b) t f))))

(define quote (vau (x) _ x))

■ Qoppa is a Scheme without special forms: all arguments are evaluated before entering the method

■ Vau is the only explicitly evaluating primitive (no automatic evaluation)

■ Vau is used to implement all other special forms

Multi-level Debugging for Intrepreter Developers, LaMOD’16, 15.03.2016, Bastian Kruck

Scheme embedded in Qoppa

Chart 6

Scheme

Qoppa

(define if (vau (b t f) env (eval env (bool (eval env b) t f))))

(define quote (vau (x) _ x))

Smalltalk

Embedded in

Interpreted by


How to teach language barriersto a debugger?

The common symbolic debugger

Chart 8Multi-level Debugging for Intrepreter Developers, LaMOD’16, 15.03.2016, Bastian Kruck

The Minimal Feature Set of a Debugger

Chart 9

Step buttons

Call Stack

Helps to zoom frombehavioral

overview into detailOverview

Detail

Source View

Helps to look at the past and

futureFuture

Past

Object InspectorHelps to interact with state of the current

Level of details

• Detail State• Detail State• Detail State


eval:in:

Call stack of QoppaS



Chart 11

operate:on:in:



Chart 12

Operative>>in:operateOn:



Chart 13

wrapPrim:countingArgs:



Chart 14

buildGlobalEnv



Chart 15

• Recurrence Patterns in call stacks signal an unnoticed abstraction level

• The varying barrier-width makes it hard to read

• Debugger users should be able to:

• Filter stack frames• Fold open levels on

demand


Higher-level information are encoded in all those

Chart 16

Step buttons

Call Stack

Various barrier- widths are present

in the call chainOverview

Detail

Source ViewSource code implements

abstract concepts such as events or state machinesFuture

Past

Object InspectorData contain

implementation specifica such as storage

strategies

• Detail State• Detail State• Detail State


How to teach language abstraction barriersto a debugger?

■ Data abstraction enables modularity□ Isolate math domain implementation□ Isolate abstract type□ Isolate representation details

■ Behavioral black-box abstractions toenable modularity

■ Not present in current debugging tools■ Interpreters form a new layer of abstractions

that is loosely coupled to the lower one□ because of that very explicit interface□ A program is the interpreters data

Abstraction barriers should be respected in debuggers

Chart 18

Structure and Interpretation of Computer Programs


Current debuggers that respect abstraction barriers:■ Rails BacktraceCleaner

■ Visual studio with Show only my code

■ Eclipse with Step filters

□ AOP & COP□ Code metrics

■ Squeak UnhandledException

■ Squeak Step through

There is no general abstraction-aware debugger so far

(Current state of abstraction barriers in debuggers)


(define (fact-r n acc)(if (<= n 1)(begin (halt) acc)(fact-r (- n 1) (* acc n))))

(fact (- 5 2))

Example of a Multi-level Debugger




Chart 23


Chart 24

Grouping frames by interpreter frames


Chart 25

Specialized Representation

Grouping frames by interpreter frames




Chart 27


Chart 28

Level icons show level affiliation

Chart 29

Filter levels to focus

e.g. Smalltalk Packages, or

Authoring sessions


■ By package■ By class■ By author■ By creation time■ By JIT-Optimization-State

(Identifying levels)


Implementation of both

Language barriers

Abstraction barriers

„A mediator is a software module that exploits encoded knowledge about certain sets or subsets of data to create information for a higher layer of applications“ [Wie92]

Mediator-Wrapper-Architecture

Chart 32

Mediator

Higher levelinformation

Encoded Knowledge

DataData

Gio Wiederhold: “Mediators in the Architecture of Future Information Systems”


Mediators enrich call frames

Chart 33

TitleIconGroupSourceData State

Multi-level Debugger

INOUT



Mediator-Wrapper-Architecture

Chart 34

Squeak VM

Reflection: Squeak contexts

Vivide

QoppaS Interpreter

Squeak Primitives

Qoppa Language

…

Multi-level

Debugger

…

WIP

Future Work: Debugger Primitives

Chart 35

Multi-level Debugger Scheme

Language

Squeak asimplementation language

Qoppa asimplementation language

Qoppa Language

DebuggerPrimitive

■ Reuse low-level debugger for higher levels

■ Cross level functionality comes for free



Thanks for your frameworks and support:Marcel Taeumel (VIVIDE),Patrick Rein (OhmS)Thanks to Mod16 and SWA Group for funding


[1] Charles, P. et al. 2009. Accelerating the creation of customized, language-Specific IDEs in Eclipse. ACM Sigplan Notices. 44, 10 (2009), 191.[2] Chiş, A. et al. 2015. Practical domain-specific debuggers using the Moldable Debugger framework. Computer Languages, Systems and Structures. 44, (Dec. 2015), 89–113.[3] Chiş, A. et al. 2015. The moldable inspector. 2015 ACM - Onward! 2015 (New York, New York, USA, Oct. 2015), 44–60.[4] Erdweg, S. et al. 2012. Language Composition Untangled. LDTA ’12. (2012).[5] Freudenberg, B. et al. 2014. SqueakJS A Modern and Practical Smalltalk that Runs in Any Browser. DLS ’14. (2014), 57–66.[6] Pavletic, D. et al. 2014. Extensible Debuggers for Extensible Languages. Softwaretechnik-Trends. 33, 2 (2014), 51–52.[7] Pavletic, D. and Raza, S.A. 2015. Multi-Level Debugging for Extensible Languages. Workshop Software-Reengineering und -Evolution. 17 (2015), 21–23.[8] Renggli, L. et al. 2010. Embedding Languages Without Breaking Tools. ECOOP. (2010), 380–404.[9] Wu, H. et al. 2004. Debugging Domain-Specific Languages In Eclipse. Eclipse Technology Exchange Poster. (2004), 1–5.

Related Work


Debugger Primitives■ How to bake them into the known reflective capabilities of languages?

Challenges
