Turing's First Example

Turing's 1936 first example, modelled as a true Turing machine rather than a hard-coded loop. The tape is a chain of Cell entities and the read/write head is a single Head entity holding a reference to the cell under it. The head cycles through four states — b prints a 0 and steps right, c steps right, e prints a 1 and steps right, f steps right — so the tape fills with the sequence 0 _ 1 _ 0 _ 1 _ … forever. There is no halt state; the machine runs as long as you let it.

The smallest possible introduction to the modelling pattern shared by every Turing scenario: a one-dimensional tape that extends itself on demand. When the head needs a square that does not yet exist, the current cell spawns a new neighbour, wires up the left/right references, and goes passive again — so the tape is always exactly as long as the computation has reached, with no global scan and no pre-allocated bound.

# turing-first-example.osi.yaml — emitted automatically
semantic_model:
  name: "turing-first-example"
  source: "duckdb://turing-first-example.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'"