Flow and algorithm

Platform spec article

Flow and algorithm

Back to Console I/O streams ◎ Open feature in platform map

Spec standingStandard

Owner

Piotr Mikstacki pmikstacki@cybernomad.it

Submitter

Piotr Mikstacki pmikstacki@cybernomad.it

Current document

ADRs (3)

1. 0010-split-stream-modules Split stream modules per fd Accepted

   stdin/stdout/stderr use separate System modules.

   Context

   A single Console IO type obscures direction and syscall descriptors.

   Decision

   Rule	Detail
   Modules	System.Input, System.Output, System.Error
   Forbidden	Monolithic console IO type for standard streams

   Consequences

   Each module binds one StandardStream descriptor; cross-stream APIs stay separate.

   Verification anchors

   packages/runtime/src/System/Input.bd, Output.bd, Error.bd.

   Open full ADR page

2. 0011-write-panic-read-result Write panics; read returns Result Accepted

   Syscall write failures panic; reads surface Result.

   Context

   v1 write helpers are infallible at the type level; read paths need explicit error handling.

   Decision

   Rule	Detail
   Write	Write / WriteLine must panic on WriteWith failure
   Read	Read / ReadLine return Result<string, SyscallError>

   Consequences

   Diagnostics for write failures use fixed panic strings; callers cannot catch write errors in Beskid v1.

   Verification anchors

   Corelib stream tests; syscall integration in beskid_runtime.

   Open full ADR page

3. 0012-writeline-unix-lf WriteLine emits Unix LF Accepted

   WriteLine appends a single LF byte sequence.

   Context

   Cross-platform hosts may translate line endings below the Beskid API.

   Decision

   Rule	Detail
   Ending	WriteLine must append \n only
   Windows	Host/platform layer may translate later without API change

   Consequences

   Authors see consistent Beskid source semantics; CRLF is not encoded in corelib strings.

   Verification anchors

   Output.bd / Error.bd tests; platform IO docs.

   Open full ADR page

Articles

• Contracts and edge cases MUST rules for standard stream reads, writes, and error handling. article Standard Reviewed Thu May 21
• Design model Stream module boundaries and syscall descriptor model for standard I/O. article Standard Reviewed Thu May 21
• Examples Standard stream read and write usage patterns. article Standard Reviewed Thu May 21
• Flow and algorithm Read and write algorithms for standard stream helpers. article Standard Reviewed Thu May 21
• Verification and traceability Runtime syscall and corelib anchors for standard stream I/O. article Standard Reviewed Thu May 21

History

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Completeness

OKfeature · 3 SpecSection(s) · 1 H2 heading(s)

Section id	Required	Found
what-this-feature-specifies	yes	yes
implementation-anchors	yes	yes

Full tree: run pnpm verify:platform-spec-layout (writes src/generated/platform-spec-layout-report.json).

Related spec docs

• Feature
  Console I/O streams

  Parent feature hub

Purpose

Document flow and algorithm for the Console Io Streams feature: role-specific normative detail beyond the feature hub.

Canonical references

• Feature hub: Console Io Streams
• Sibling articles in this bundle (design model, contracts, flow, examples, verification)

Detailed behavior

Write path

1. Caller supplies a Beskid string (UTF-8).
2. Module builds WriteRequest with Descriptor::Standard(Stdout | Stderr) and payload bytes.
3. Syscall.WriteWith invokes __syscall_write.
4. On Result::Error, module panics with the stable panic string (IO-004).

WriteLine chains two writes; callers should not embed \n in text when using WriteLine unless a double newline is intended.

Read path (ReadLine)

1. Loop ReadWith on stdin with a byte limit until:
   • buffer contains \n → return slice before newline, or
   • EOF / error → return Result per syscall mapping.
2. No ANSI parsing occurs; escape bytes in stdin are returned literally to the caller.

Console tick integration

Console.RunTick polls resize and may write control sequences via System.Output after formatting. The tick loop should run on a fiber that owns the terminal UI; see Console terminal events.

Styled output flow

Markup or Ansi builders → gated string → System.Output.Write / WriteLine. Capability probing runs before write, not inside Output.bd.

Verification

See the verification and traceability article in this bundle and compiler/corelib/beskid_corelib/tests/corelib_tests/src/console/.

Related topics

• Parent feature hub and Terminal and console area