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fsharp-type-provider.md

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F# Type Provider for FScript Exports

This specification defines the contract for MagnusOpera.FScript.TypeProvider.

Purpose

  • Compile-time parse and type-check .fss scripts.
  • Expose [<export>] functions as strongly-typed static methods in F#.
  • Allow runtime script replacement with strict signature compatibility checks.

Provider entry point

  • Namespace: FScript.TypeProvider
  • Type provider: FScriptScriptProvider

Static parameters:

  • ScriptPath: string (required)
  • RootDirectory: string (optional, defaults to script directory)
  • ExternProviders: string (optional, semicolon-separated assembly-qualified provider type names)

Compile-time behavior

  1. Resolve script path and root directory.
  2. Resolve externs using runtime defaults plus configured extern-provider types.
  3. Parse with includes from file and run type inference.
  4. Collect exported functions.
  5. Fail compilation on:
    • parse/type errors,
    • unsupported exported signature shapes.

Exposed members

For each exported function, generate one static method with mapped .NET/F# types.

Provider-generated static members:

  • SetRuntimeResolver : (unit -> RuntimeScriptOverride option) -> unit
  • ClearRuntimeResolver : unit -> unit

RuntimeScriptOverride fields:

  • RootDirectory: string
  • EntryFile: string
  • EntrySource: string
  • ResolveImportedSource: (string -> string option) option

Supported exported signature mapping (v1)

Supported:

  • unit
  • int -> int64
  • float
  • bool
  • string
  • list<T>
  • option<T>
  • tuples (arity 2..8)
  • map<string, T> -> Map<string, T>

Rejected:

  • records
  • unions
  • named/custom types
  • function values in argument/return positions
  • unresolved type variables
  • non-string map keys

Runtime compatibility policy

  • Provider computes a compile-time fingerprint of all exported function signatures.
  • Every invocation loads script via compile-time path or active runtime resolver override.
  • Runtime exported signature fingerprint must exactly match compile-time fingerprint.
  • Mismatch fails invocation with an error before function execution.

Runtime load source selection

  • No resolver set: load compile-time script file.
  • Resolver set and returns Some: load EntrySource with loadSourceWithIncludes and optional import resolver.
  • Resolver set and returns None: fallback to compile-time script file.