Commits on Apr 8, 2026

1. Better CE Builder …

   Task 2: Allow if! and for! tokens - lexer, parser, LexFilter,
   LanguageFeatures
   
   - Add IF_BANG and FOR_BANG token rules in lex.fsl
   - Add token declarations and grammar rules in pars.fsy
   - if! desugars to MatchBang with bool pattern clauses at parser level
   - for! desugars to ForEach with isFromSource=false (no Source wrapping)
   - Add IfBang and ForBang language features (preview)
   - Handle new tokens in LexFilter.fs and ServiceLexing.fs
   
   Task 5: Desugar while! to recursive Bind/Combine/Zero (carrier-free)
   
   Replace the old while! desugaring (which required While(unit->bool,...))
   with
   a recursive Bind/Combine/Zero pattern that only requires Bind, Combine,
   and Zero.
   
   while! guard do body now desugars to:
     let rec __whileLoop () =
         builder.Bind(guard, fun __res ->
             if __res then
                 builder.Combine(translatedBody, builder.Delay(fun () ->
   __whileLoop()))
             else
                 builder.Zero())
     __whileLoop()
   
   Fix BindReturn poisoning do!, add tests and documentation
   
   - When consumePat is a unit pattern (from do! desugaring), skip
   BindReturn
     optimization and fall back to Bind + Return. This prevents FS0001 when
     a builder defines BindReturn(M, M->M) but do! produces unit->unit.
   - Add CEEnhancementsTests.fs with 13 tests covering:
     - BindReturn/do! poisoning fix
     - if! desugaring with else, without else, version gating, missing Bind
     - for! desugaring without IEnumerable constraint, version gating
     - while! carrier-free desugaring
     - Regression tests for async, task, seq
   - Add docs/ce-enhancements/CHANGES.md and RFC-DRAFT.md
   
   Improve BindReturn fix comment to clarify Bind overload selection
   
   FS0041 fix: type-annotate unit continuation in CE Bind to disambiguate
   overloads
   
   When consumePat is a unit pattern (from do! desugaring), wrap the
   continuation MatchLambda in SynExpr.Typed with (unit -> _) annotation.
   This gives overload resolution enough type info to disambiguate between
   Bind(M, unit -> M) and Bind(M, Expr -> M) without FS0041.
   
   Add comprehensive tests for mixed let!/do!/and! with overloaded Bind
   and BindReturn, including FS0041 regression tests.
   
   WIP: WhileBang builder method + comprehensive tests (40/40 pass, 0
   regressions)
   
   feat(compiler): wrap while! guard in builder.Source and add design docs
   
   Updated while! desugaring to pass the guard through builder.Source
   before WhileBang, ensuring consistency with let! and match!.
   Updated CheckComputationExpressions.fs to include the Source call.
   Added "Design Principles" section to RFC-DRAFT.md outlining the minimal
   extension approach for CE enhancements.
   Updated CHANGES.md to reflect the technical desugaring change.

   

   aiqs4 committed Apr 8, 2026
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