Alex

Alex is the witness stage of the Composer compiler for the Clef language. It reads one published revision of the Program Semantic Graph (PSG) and emits MLIR.

Alex was part of the Composer repository until September 2026, as the directory src/MiddleEnd. It is now its own project, so that the separation between the compiler service and the witness stage is a fact of the build.

What Alex depends on

Dependency	Purpose
Fidelity.PSG	The published form of the PSG. It is its own project. The compiler service produces revisions of it, and Composer hands one to Alex. This is the only description of a program Alex receives.
BAREWire	The library the contract references for declared platform types. It reaches Alex through the contract.
XParsec	Parser combinators. Patterns are composed with them.
FSharp.Core	The host language's core library, for as long as .NET hosts the compiler.

Alex does not reference the Clef Compiler Service. The build refuses a source line that names it.

Entry

Alex.Generation.generate : Request -> Result<Witnessed, Refusal>

A Request holds the revision, the selected target, and the libraries the project declares. The entry examines the revision with the structural rules of the contract (Fidelity.PSG.Integrity.check) and refuses one that is not well formed before any witness runs. A Witnessed value holds the operations, their portable text, the correspondence records, the writable storage inventory, the transcription of the proof obligations, and the link requirements. A Refusal holds the reason and the operations witnessed before the refusal.

Layout

Path	Content
src/Alex/Dialects	MLIR types and operations, and their serialization to text
src/Alex/Elements	One MLIR operation each
src/Alex/Patterns	Compositions of Elements over published facts
src/Alex/Witnesses	One category of node each
src/Alex/Traversal	The Huet zipper, the single traversal, value names, coverage checks
src/Alex/XParsec	Combinators over the revision
src/Alex/Correspondence.fs	Scope, occurrence and emitted-definition records
src/Alex/Generation.fs	The public entry
build/Boundary.targets	The boundary, checked before every compile
tests/Alex.Tests	Tests of Patterns, witnesses and the traversal, given revisions assembled from contract values
docs	The boundary, the contract, the open decisions, the debt register and the account of the tests
tools	CcsSurfaceInventory.fsx measured the dependency on the compiler service. PlanMeasure.fsx measures what the edge set of a revision says about units of work.

Build

dotnet build src/Alex/Alex.fsproj

The contract is expected at ../Fidelity.PSG/src/Fidelity.PSG/Fidelity.PSG.fsproj. A different location is set in Directory.Build.local.props through the property PsgContractProject.

dotnet test tests/Alex.Tests/Alex.Tests.fsproj

docs/05_Tests.md states what a test is given and how one file is run alone.

State

Alex builds against the contract alone. Composer references this project, asks the compiler service to publish a revision, and hands the revision to Alex.

The revision is an immutable value in memory. Its binary form is not yet built. The documents in docs state what is decided, what is proposed and what is owed.

History

The files under src/Alex were copied from Composer at commit 896ef98. Their earlier history is in the Composer repository under src/MiddleEnd.