`lsystem2`

is a 2D implementation of L-system. It's based on the algorithm of turtle grahpics. Instructions for generation of rules are as follows:

```
F Move forward and draw line
f Move forward without drawing a line
+ Turn left
- Turn right
| Reverse direction (ie: turn by 180 degrees)
[ Push current turtle state onto stack
] Pop current turtle state from the stack
```

**Since:** 2.4

## Parameters

`axiom`

: The initial state of the system.`rules`

: A list of production rules. The first element of each rule is the predecessor, and the second is the successor.`n`

: Iteration times.`angle`

: Used when turing.`leng`

: Used when forwarding. Default to`1`

.`heading`

: The initial angle of the turtle. Default to`0`

.`start`

: The starting point of the turtle. Default to`[0, 0]`

.`forward_chars`

: Chars used for forwarding after the last iteration. Default to`'F'`

.`rule_prs`

: The probabilities for taking rules. If each rule is chosen with a certain probability, it's a stochastic L-system. Each probability value for a rule ranges from 0 to 1.

## Examples

lsystem2-collections.scad collects several L-system grammars. Here's one of them.

```
use <turtle/lsystem2.scad>;
use <line2d.scad>;
for(line = fern()) {
line2d(
line[0],
line[1],
.2,
p1Style = "CAP_ROUND",
p2Style = "CAP_ROUND"
);
}
function fern(n = 8, angle = 4, leng = 1, heading = 0, start = [0, 0]) =
let(
axiom = "EEEA",
rules = [
["A", "[++++++++++++++EC]B+B[--------------ED]B+BA"],
["C", "[---------EE][+++++++++EE]B+C"],
["D", "[---------EE][+++++++++EE]B-D"]
]
)
lsystem2(axiom, rules, n, angle, leng, heading, start, forward_chars = "ABCDE");
```

```
// a stochastic L-system
use <turtle/lsystem2.scad>;
use <line2d.scad>;
for(line = weed()) {
line2d(
line[0],
line[1],
.2,
p1Style = "CAP_ROUND",
p2Style = "CAP_ROUND"
);
}
function weed(n = 6, angle = 22.5, leng = 1, heading = 0, start = [0, 0]) =
let(
axiom = "F",
rules = [
["F", "FF-[XY]+[XY]"],
["X", "+FY"],
["Y", "-FX"]
]
)
lsystem2(axiom, rules, n, angle, leng, heading, start, rule_prs = [0.8, 0.8, 0.8]);
```