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Stratego. Song Zhou *Include slides from Introduction. Stratego is “ a language for the specification of transformation systems based on the paradigm of program rewriting strategies ” . Basic components:

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Song Zhou

*Include slides from


  • Stratego is “a language for the specification of transformation systems based on the paradigm of program rewriting strategies”.

  • Basic components:

    • Rules: basic transformation steps

    • Strategies: control application of rules

Stratego xt

  • Stratego is only a term-rewriting language. “Term in, Term out.” XT can combine Stratego with other tools to create a transformation system.

  • Front End:

    • SGLR: a generic parser creating syntax tree

  • Back End:

    • GPP: a generic pretty-printer to emit the syntax tree out

  • Communication Language

    • Aterm: a term exchange format

What is wrong with abstract syntax
What is wrong with Abstract Syntax

  • Problems

    • Easy for computer to process

    • Difficult for human being to read and write

    • Maybe to verbose to be specified

  • Solution

    • Directly employ the concrete object syntax to specify the rewriting rules in Stratego

Mix an object language with a meta language
Mix an Object Language With a Meta Language

  • Object Language inside Meta Language:

    • Extending Meta Language witha quotation operator that lets the meta-programmer indicate object languagefragments.

  • Meta Language inside Object Language:

    • Antiquotation allows the use of meta-programming languageconstructs in these object language fragments to splice meta-computed objectcode into a fragment.

  • If Meta Language equals Object Language then the syntax extension is easy by justadding quote and antiquote operators to Meta Language.


  • EvalPlus : |[ i + j ]| -> |[ k ]|where <add>(i, j) => k

  • TraceProcedure : |[ function ~f(~* xs) = ~e ]| -> |[ function ~f(~* xs) = (print(~String(<conc-strings>(f," entry\\n"))); ~e; print(~String(<conc-strings>(f,"exit\\n"))))]|

Syntax definition formalism
Syntax Definition Formalism

  • Both the Stratego syntax and the object language syntax is specified using the Syntax Definition Formalism (SDF)

  • AnSDF production sym1 ... symn -> sym declares that an expression of sort symcan be constructed by the concatenation of expressions of sorts sym1 to symn.

  • SDF supports regular expression operators such as {Exp ";"}*, which denotesa list of Expressions separated by ; semicolons.

  • SDF integrates thedefinition of lexical and context-free syntax in one formalism.

  • The formalismis modular

    • the syntax definition of a language can be divided intosmaller (reusable) modules

    • syntax definitions for separate languages caneasily be combined.

Tiger s yntax d e fi nition in sdf
TigerSyntax Definition in SDF

Corresponding a bstract s yntax s ignature
Corresponding Abstract SyntaxSignature

Syntax combination
Syntax Combination

  • The object language syntax definition can be imported into Stratego syntax definition

  • We also need define an additional combinationial syntax definiton, to specify the glues (quotation mark and antiquotaion mark)

Theoretical problems
Theoretical Problems

  • Only full class of CFG have closure property. LL, LR and other subclasses of CFG are not closed under composition.

  • SDF2 supports scannerless generalized-LR parsing

Generic d e fi nition of m eta explode
Generic termDefinition of Meta-explode

Summarize term

  • Rules rewriting

  • Transformation strategy

  • First-Class Pattern Matching

  • Scoped Dynamic Rewrite Rules

  • Concrete Object Syntax