introducing static semantic analysis to templates using jastadd

Introducing Static Semantic Introducing Static Semantic Analysis to Templates Analysis to Templates Using JastAddUsing JastAddJos PeetersJos Peeters

/ name of department PAGE 204/22/23

Goal

Ambition• Improve the quality of code generators based on templates.

Primary Research Question• Can static semantic checking be used in template-based code

generators using off-the-shelf tooling?


Research Questions

• Can JastAdd be coupled to Repleo?• Is the resulting coupling scalable?

• How can static semantic checking be performed on templates?• How to deal with syntactic ambiguities?• How to implement this using JastAdd?


• Research Questions• Tools

• Repleo• JastAdd• Connection

• Methodology • Placeholders• Static Semantic Checking• Syntactic Ambiguities

• Implementing the Methodology• Conclusion


Tools

• Repleo• Syntax-safe template engine

• JastAdd• Java-based compiler compiler system• Object-oriented abstract syntax• Advanced attribute grammar features


Repleo

• Templates• Architectural Pattern• Code with empty spaces and generative commands

• Features• Guarantees syntax-safe output code• Provides meta-language for templates


Repleo


JastAdd

• Features• Abstract Syntax• Parser Independent• Extended support Attribute Grammars• Aspect Oriented


JastAdd


Abstract syntax

abstract BlockStmt;abstract Stmt: BlockStmt;

AssignStmt : Stmt ::= Variable:Access Value:Exp;WhileStmt : Stmt ::= Condition:Exp Body:Stmt;

abstract Exp;abstract Access:Exp;IntLiteral : Exp ::= <Value:String>;

abstract Operator : Exp;abstract BinOperator : Operator ::= lhs:Exp rhs:Exp;PlusOp : BinOperator;


Attributes

Properties as attributes• Synthesized• Inherited• Equations

Also:• Rewrites• Circular attributes• Non-terminal attributes


Weaving Aspects

aspect TypeAnalysis { syn lazy TypeDecl Exp.type();

eq BinOperator.type() { if (getlhs().type().isSubtypeOf(getrhs().type()) || getrhs().type().isSubtypeOf(getlhs().type()) )

{ if (getlhs().type().isUnknown() )

return getrhs().type(); return getlhs().type(); } return unknownDecl().type(); }

eq IntLiteral.type() = intType();}


Connection

• Boolean Evaluator• Simple boolean expressions

• Java 1.4• Using JastAddJ


Connection


Connection JastAddJ

Issues• No strict separation between checker and parser

• Instantiation parts of checker• Rewriting during parse phase• Grammar differences between SDF and AST

For placeholder a 1-to-1 transformation is required


Placeholders(1)

What are placeholders?• Representation of empty space in code• Substitution or generative command• Properties defined by place of occurrence

"<:" TreeQuery ":>" -> PlaceHolderSubstitution[[X]]


Placeholders(2)

Substitutionint <: x :>;

Conditional<: if x == "true" then :> boolean b; <: else :> int i; <: fi :>


Placeholders (3)

Iterativeint i = 0;<: foreach $x in X do :> i = i + <: $x :>;<: od :>

Match-Replaceint i = 0;i = <: match X :> <: [$e,$t] = :> <: $e :> + <: $t :> <: [] = :> 0<: end :>;


Static Semantic Checking

• Target language• Type checking• Context related checks (f.i. duplicate declarations)

• Placeholders language• Uniqueness meta-variables (i.e. $e)

• Combination of both• Checking influence of placeholders on target language• “Bad Smells”


Bad Smells

Not permitted• errors that are related to properties of placeholders

<: foreach $x in X do :> int i;<: od :>

Permitted• restrictions given only by the input data

<: foreach $x in X do :> int <: $x :>;<: od :>


Syntactic Ambiguities

• Occur when multiple production can be applied• Parsing problem

• SGLR• Bad Smell

public class A { <: a :> <: b :>(){}}


Disambiguation

• Via Context• Use static semantic checker• Compare previous use of placeholders

public class A { <: a :> i = 0;

<: a :> <: b :>(){}}


Disambiguation

• Using prioritization• Select the option

containing the placeholder

{ int i; i = <: a :>;}


Implementing the Methodology

PicoJava• Subset of Java• Originally an example of JastAdd

Present• PicoJava language definition in JastAdd• Attributes to support checking• Static semantic checker• SDF definition Placeholders


Pipeline


Implementation

Implemented as part of this project• SDF definition PicoJava• Traversal SGLR JastAdd

With JastAdd• Language definition placeholders• Extend attributes for the placeholders• Static semantic checker

• Placeholders• Bad Smells

• Ambiguity nodes• Disambiguation filter

NB. JastAdd is Aspect-Oriented


Example - Template

template({ <: if x == $e then :> boolean i; i = <: match y :> <: [$e, $t] = :> <: $e :> + <: $t :> <: [] = :> 0 <: end :>; <: fi :> i = 0; })

123456789

101112


Example – Output(1)

--> Resolving ambiguities 6:21 Ambiguity found: Exp Ambiguity resolved using prioritization 6:32 Ambiguity found: Exp Ambiguity resolved using prioritization Done


Example – Output(2)--> Language Errors 10:2 : Can not assign to a variable of type boolean a value of type int

--> Placeholder Errors6:6 : duplicate declaration of meta-variables [$e]

--> Placeholder Bad Smells 7:6 : inferred type of placeholder does not match the type of its declaration

10:2 : Variable i might not be declared, dependent on [x]

--> List of PlaceHolders $e PhExp $unknown $unknown $t PhExp $unknown $unknown y PhMRExp $unknown int x PhIfBlockStmt $unknown $unknown


Conclusions

Presented in this Thesis• Static Semantic Checks on Template• Use of off-the-shelf tools

• Repleo• JastAdd

Methodology• Multi-language approach• Ease-of-use of templates• Syntax-safe• Static Semantic Analysis


Questions

introducing static semantic analysis to templates using jastadd

Documents

type getrhs

type return getlhs

type eq binoperator

static semantic analysis

exp body

exp rhs

expabstract binoperator

templatebased code generators