4. Signature Generator

It is quite cumbersome to write Statix signatures. Thankfully, the sdf3.ext.statix project can generate these signatures for you.

4.1. Well-Formed SDF3 Requirements

For the generator to work correctly, your SDF3 must be well formed. In particular, you must:

  • explicitly declare each sort exactly once in your project
  • declare lexical sorts in a lexical sorts block
  • declare context-free sorts in a context-free sorts block
  • for every use of a sort: either have a local declaration of a sort, or an import of a file that declares the sort
  • not declare sorts that are not used in any rules
  • not use any implicitly declared sorts
  • not use complex injections, such as Pair = Expr Expr
  • not use optional terms, such as Decl.VarDecl = ID Type?
  • not use sdf2table: c

The generator generates strategies and signatures for each explicit declaration of a sort in SDF3, which is why each sort must be declared exactly once. SDF3 does not generate Stratego signatures for placeholders for sorts that have no corresponding rules, causing errors in the generated Statix injection explication strategies. Complex injections are not supported across Spoofax. Optional sorts cannot be represented in Statix.

4.2. Applying the Generator in Spoofax 2

In your language project’s metaborg.yaml file, change your compile dependencies to include org.metaborg:sdf3.ext.statix. For example:

dependencies:
  compile:
  - org.metaborg:org.metaborg.meta.lang.esv:${metaborgVersion}
  - org.metaborg:org.metaborg.meta.lang.template:${metaborgVersion}
  - org.metaborg:sdf3.ext.statix:${metaborgVersion}
Note: Clean the project and restart Eclipse when changing the metaborg.yaml file.

Once you clean your project, the extension automatically generates the following:

  • Statix signatures declarations (in src-gen/statix/signatures/)
  • Stratego strategies for explicating and removing injections (in src-gen/injections/)

4.3. Using the Generated Injection strategies

The generator generates strategies for explicating and removing injections. This is unfortunately needed since Statix does not support injections directly. To use these strategies, import injections/- and call the explicate-injections-MyLang-Start and implicate-injections-MyLang-Start strategies for the analysis pre-processing and post-processing respectively, where MyLang is the name of your language and Start is your language’s start symbol (as specified in Syntax.esv). For example, in trans/analysis.str:

module analysis

imports

  libspoofax/sdf/pp

  statixruntime
  statix/api

  injections/-

rules

  editor-analyze = stx-editor-analyze(pre-analyze, post-analyze|"static-semantics", "programOk")
  pre-analyze  = explicate-injections-MyLang-Start
  post-analyze = implicate-injections-MyLang-Start

4.4. Using the Generated Signatures

Using the generated Statix signatures is quite simple: just import them into your Statix specification. Each SDF3 file gets an associated Statix file with the signatures. For example, if your syntax is defined across two files named MyLang.sdf3 and Common.sdf3, then in Statix you should add the following imports:

imports
  signatures/MyLang-sig
  signatures/Common-sig

Because Statix does not support injections, you have to use explicit constructor names for injections. For example, the following SDF3 syntax:

context-free sorts
  Stmt VarName

lexical sorts
  ID

context-free syntax
  Stmt.VarDecl = <var <VarName>;>
  VarName.Wildcard = <_>
  VarName = ID

lexical syntax
  ID = [a-zA-Z] [a-zA-Z0-9\_]*

lexical restrictions
  ID -/- [a-zA-Z0-9\_]

would approximately produce the following signatures:

module signatures/Test-sig

imports

signature
  sorts
    Stmt
    VarName
    ID = string
  constructors
    Stmt-Plhdr : Stmt
    VarName-Plhdr : VarName

signature
  constructors
    VarDecl : VarName -> Stmt
    Wildcard : VarName
    ID2VarName : ID -> VarName

Now, in Statix if you just want to capture the term of sort VarName in the VarDecl constructor, this would suffice:

VarDecl(x)

But if you want to match the term only if it has the sort ID, then you have to use the explicit injection constructor name ID2VarName:

VarDecl(ID2VarName(x))

In this example, ID is a lexical sort, so it is an alias for string in the Statix specification.

4.5. Troubleshooting

4.5.1. Calls non-existing

Build fails with errors such as this:

[ strj | error ] *** ("is-MyLang-MySort-or-inj",0,0) calls non-existing ("is-MyLang-ID-or-inj",0,0)
[ strj | error ] *** ("explicate-injections-MyLang-MySort",0,0) calls non-existing ("explicate-injections-MyLang-ID",0,0)
[ strj | error ] *** ("implicate-injections-MyLang-MySort",0,0) calls non-existing ("implicate-injections-MyLang-ID",0,0)
Executing strj failed: {}
Failing builder was required by "Generate sources".
BUILD FAILED

To solve this, ensure you have declared ID (in this example) as a lexical sort in your syntax, and make sure that the syntax file with rules for MySort that reference ID import the syntax file that declares ID.

4.5.2. Transformation failed unexpectedly

Clean or build fails with an error such as this:

ERROR: Optional sorts are not supported by Statix: Opt(Sort("MySort"))
Transformation failed unexpectedly for eclipse:///mylang/syntax/mysyntax.sdf3
org.metaborg.core.transform.TransformException: Invoking Stratego strategy generate-statix failed at term:
  CfSignature("MySort", Some("MyCons"), [ Param(Opt(Sort("MySort")), "mySort") ])
Stratego trace:
  generate_statix_0_0
  generate_statix_abstract_0_0
  geninj_generate_statix_0_0
  geninj_module_to_sig_0_0
  with_1_1
  flatfilter_1_0
  filter_1_0
  with_1_1 <==
  map_1_0
  geninj_symbol_to_stxsig_0_0
Internal error: 'with' clause failed unexpectedly in 'geninj-sig-to-stxsig'

Note the first line with ERROR, it tells you that something is not supported. In this case, the use of optional sorts such as MySort? is not supported by Statix and the Statix signature generator.

To solve this, rewrite a syntax rule with an optional sort such as:

Stmt.VarDecl    = <<Type?> <ID> = <Exp>>

Into a rule with an explicit sort:

Stmt.VarDecl    = <<Type-OPT> <ID> = <Exp>>
Type-OPT.NoType = <>
Type-OPT        = Type

Note that the -OPT suffix has no special meaning. You can name the sort differently, such as OptionalType.

4.5.3. Constructor MySort-Plhdr/0 not declared

Buid fails with an error such as this:

[ strj | error ] in rule explicate-injections-MyLang-MySort(0|0): constructor MySort-Plhdr/0 not declared
-     MySort-Plhdr()
Executing strj failed: {}
BUILD FAILED

You have declared a sort for which you don’t have any rules. Remove the sort from the context-free sorts or sorts block.

4.5.4. No pp entry found, cannot rewrite to box

Clean fails with an error such as this:

[ identity crisis | error ] No pp entry found for: (1,["declSortLex"])
- [ identity crisis | error ] Cannot rewrite to box:
-         declSortLex("MySort")

You are using the old sdf2table: c. Change this in metaborg.yaml into sdf2table: java.