Palindrome Decider

A decider that erases matching ends and sweeps inward — halting in Accept or Reject.

Sync Tick Turing

Try it live→ Download Database

Machine replay — erasing matching ends, halting in Accept FULLSCREEN ⤢

Clock Tick — one step per turn

Update Synchronous

States 6 + Accept / Reject

Symbols 3 (blank, a, b)

Halts Accept or Reject

OVERVIEW

A genuine decider — a machine that halts with a yes/no answer. Over the alphabet { a, b } it remembers the first symbol in its control state, erases it, walks to the opposite end, and checks the symbol there matches what it remembered; if so it erases that too and turns back. The input shrinks from both ends until either the tape is empty (Accept) or a mismatch is found (Reject). The seeded input abba is a palindrome, so the head finishes in the Accept halt state.

The counterpoint to the non-halting examples: a machine that terminates with a decision. It exercises both halt states, the remember-in-state trick that lets a finite control compare two distant symbols, and the full two-directional sweep over a bounded tape — a compact, fully observable test of accept/reject reasoning.

TRAITS

Sync

Advances on a single global clock

Tick

Discrete fixed-step time

Turing

A head reads & writes an unbounded tape

SCHEMA

Linked tables with guaranteed referential integrity.

TABLECOLUMNSDESCRIPTION

cell ID, symbol, left_id, right_id, current_state One row per tape square over { blank, a, b }, with left/right neighbour references; squares are erased to blank as the ends are matched.

head ID, current_id, nc, current_state The read/write head: the cell beneath it and its control state, including the Accept and Reject halt states.

LIVE API

Generated REST endpoints. Also exposed as MCP tools.

POST /scenarios/palindrome/experiments Seed a tape with an input word

POST /scenarios/palindrome/experiments/{eid}/run Run the decider to its halt state

GET /scenarios/palindrome/experiments/{eid}/entities/head Read the head's final Accept/Reject state

GET /scenarios/palindrome/experiments/{eid}/events Append-only step log

GET /scenarios/palindrome/experiments/{eid}/dataset Download the exported dataset

SEMANTIC LAYER

OSI-compatible definition, emitted with the dataset.

# palindrome.osi.yaml — emitted automatically
semantic_model:
  name: "palindrome"
  source: "duckdb://palindrome.db"
  entities:
    - name: cell
      primary_key: id
  dimensions:
    - name: state
      type: categorical
    - name: t
      type: time
  measures:
    - name: row_count
      agg: count
    - name: active
      agg: sum
      filter: "state = 'ACTIVE'"