Rule notation

Every automaton in JETCARP has a rule, written as a short piece of text such as B3/S23 or Cyclic 14/1. The same text works everywhere: in the app’s rule box, in a scene file, on the command line, in scripts and in the MCP tools. This page lists every form the parser accepts, with its limits. The encyclopedia page for each family explains what the rules mean; this page only says how to write them.

A few things hold for every form:

• Case does not matter, and spaces are ignored except where they separate words (HexT3 sum 588). b3/s23, B3/S23 and B3 / S23 are the same rule.
• JETCARP writes rules back in one canonical form. A saved scene, a report or the app shows the canonical text, so Rule 30 comes back as W30 and B2/S/3 as B2/S/C3. The table at the end of this page shows what each example becomes.
• Names are resolved by the front ends, not by scene files. The app, the command line, scripts and the MCP tools accept a rule’s name (Life, Brian's Brain) wherever they accept notation. A scene file’s rule field must hold notation; a name there is refused with “‘Life’ is not a rule”. See Named rules.
• Some rules need a particular grid. Elementary rules, Margolus block rules and von Neumann’s 29-state rule need the square grid, the two-parent hexagon rules the hex grid and the three-parent ones the flat-top hex_flat grid. Everything else runs on any tiling. A rule that cannot run on the chosen tiling is refused with a message that says which grid it needs.

Life-like rules: B/S

B<birth counts>/S<survival counts>. A dead cell with a birth count of live neighbours is born; a live cell with a survival count survives. Either list may be empty (B2/S is Seeds). The counts may be written in any order and are sorted when written back (B32/S2 becomes B23/S2).

Only the birth-first order, with its letters, is read: the older survival/birth forms 23/3 and S23/B3 are refused.

Generations

B<birth>/S<survival>/C<states>, with 2 to 255 states. The third part may also be written without the C (B2/S/3) or with a G (B2/S/G3); JETCARP writes it with C. With two states the rule is an ordinary B/S rule (B3/S23/C2 is B3/S23). A trailing V picks edge neighbours (B2/S/C3V).

Larger than Life

Two forms, both with fields separated by commas:

The range runs from 1 to 20. C0 and C2 both mean two states; up to C255 gives Generations-style decay. Counts can be single values, ranges written a-b or a..b, or lists of both separated by commas (S2-3,5,7-9). Weighted and custom neighbourhoods (NW… and other N suffixes) are not supported yet, so a few named rules from other programs, such as Coexistence, cannot be run.

Elementary rules

W<n> or Rule <n>, with n from 0 to 255 (Rule110 and W 30 also work). They need the square grid and write one row per generation.

Hexagonal row rules: HexW and HexT

How a number is read (which digit belongs to which parents) is on the hexagonal rows page.

Layered rules

Layer <states>/<outputs> (also Layered), with 2 to 9 states and 1 to 64 output digits. Digit k is the new state of a tile whose parents’ states add up to k; the list repeats for larger sums. Every digit must be a state below the state count, so Layer 2/02 is refused. Layered rules run on any tiling.

JACA

JACA <rule for +1> [<rule for −1>] [blast <r>], where each rule is a B/S rule.

The blast radius runs from 0 to 64. Rules with birth on 0 are refused. Counts of 10 or more use commas, as in other B/S rules.

Ants and turmites

Turns are L, R, N (none), U (half the tile’s degree) and L2 and R2 (two slots); L1 and R1 are the same as L and R. A turn string has 2 to 16 turns. A table entry is <colour to write><turn><next state>; tables have up to 16 states and 2 to 16 colours, with 10 to 15 written a to f, and every state must have one entry per colour. Ants always walk across edges, whatever neighbourhood is set. How a turn is measured on tiles that are not squares is on the turmites page.

Multi-state families with parameters

Parameters follow the name, separated by slashes. Each name alone gives the defaults shown.

The cyclic automaton uses edge neighbours by default; the others use touch neighbours.

Margolus block rules

Blocks number their cells as MCell does: upper left 1, upper right 2, lower left 4, lower right 8. Named tables are written back as their 16 outputs. Margolus rules need the square grid.

Lenia

Lenia R=…,T=…,b=…,m=…,s=… with optional kn=… and gn=…. Parameters may come in any order, may be fractions (b=1/2,1), and Chan’s bracketed lists (b=[1/2,1]) are read too. Lenia alone is Orbium’s rule, Lenia R=13,T=10,b=1,m=0.15,s=0.015.

Priority tables

Priority <states>: <row>; <row>; … (PT is accepted for Priority), with 2 to 8 states and at most 64 rows. A row is <own state>|<conditions>-><next state>: the own state is a number or * for any, and the conditions are terms nS>=m (“at least m neighbours in state S”) joined by &, or always. The first row that matches wins; a cell that matches none becomes 0.

SpectreGlider (also table:spectre-glider) is James Edmond’s Spectre glider rule, the three-row table Priority 4: 0|n0>=3&n1>=1->3; 3|n3>=3->0; 3|n1>=1->1. See Priority rules and the Spectre glider.

Rule tables

Table <name> runs a rule table by name (the name is not case sensitive). One table is built in, Table parity. Other tables come from the scene’s own tables list (see the scene file format) or are loaded in the app; a name that no table has is refused when the automaton is added (“no rule table named ‘codd’”). The table format itself is on the rule tables page.

Single-word rules

Named rules

Where the front ends take a rule (the app, jetcarp commands, scripts and the MCP tools), they also take a rule’s name. Names are compared by their letters and digits only, in any case, so Brian's Brain, brians-brain and BRIANS BRAIN are one name, and Game of Life, Conway and Conway's Life are nicknames for Life. Text that is already valid notation is always read as notation first. jetcarp rules lists every name with its notation; the named rule catalogue has them all with their credits.

Scene files, again, store notation only: the app and jetcarp run --save write the notation, and the scene’s automaton keeps the name in its own name field.

Neighbourhoods

Rules that count neighbours run on touch or edge neighbours (see How JETCARP generalises automata). The notation can choose (V on a B/S, Generations or JACA rule; NM, NN and N+ on Larger than Life); otherwise an automaton’s neighborhood setting does, and the rule’s default applies when neither does. In a scene file the setting is "touch" or "edge". The command-line --nb options, script options and MCP tools also accept other names, in any case and with - or a space in place of _: moore, touching, corner, vertex, t or 8 for touch, and von_neumann, vonneumann, vn, e or 4 for edge. Ants, elementary and hexagonal row rules, Margolus rules, Lenia, Larger than Life and von Neumann’s rule fix their own neighbourhood, and the setting is ignored for them.

Checked against the program