Examples

Every example in examples/ elaborates, passes the gate and is exercised by the test suite, so none of them is a sketch that no longer runs.

Example	Shows
divider/	The smallest real board: two resistors and a capacitor
blinky/	Declared surfaces, connections and a constraint stating intent rather than the answer
equations/	Values chosen by equation and reuse by inheritance
sensor_board/	Interfaces lowering to pins, a recorded decision, a check left undecided
i2c_bus/	A multi-drop bus, addresses as constrained parameters
usb_uart_bridge/	Part selection: manufacturer, MPN, distributor and datasheet
buck_regulator/	Requirement, decision, calculations and verification beside the circuit
servo_drive/	Composition: one HalfBridge block instantiated three times

Running one

fang build   examples/sensor_board/sensor_board.py
fang netlist examples/sensor_board/sensor_board.py
fang view    examples/sensor_board/sensor_board.py ground -o ground.svg

What is in an out/

File	What it is	Command
<name>.net	The KiCad netlist, the artifact a layout tool opens	fang export
netlist.txt	The same projection as text: parts, then nets and their pads	fang netlist
checks.txt	Every check that ran, and every one left undecided	fang check
graph.txt	What the elaborated graph contains, by entity kind	fang graph
views/*.svg	The views worth looking at for that board	fang view
rationale.md	The requirements, decisions, calculations and evidence in the graph	none

python examples/regenerate.py rewrites them. They are built in the project namespace PRJ-EXAMPLES, which is where the identifiers in them come from; a local fang build defaults to PRJ-LOCAL and derives its own.

What each one is for

divider/ is the smallest thing worth calling a board. Read it to learn the shape of a program and nothing else.

blinky/ adds the point about constraints. The series resistor is not written as a number that someone computed offstage. The LED current is written as the requirement, and the resistor value has to satisfy it.

equations/ takes that further. Ohm’s law is a constraint rather than a comment, so substituting a part re-checks the arithmetic instead of trusting it. SenseDivider inherits the equations and replaces the two values.

sensor_board/ is the one to read to understand lowering. The MCU offers PB8 and PB6 for the I2C clock. self.mcu.i2c >> self.imu.i2c resolves to one of them and records a decision naming what it rejected. It also leaves a check undecided, because the IMU’s threshold is missing rather than assumed.

i2c_bus/ connects one port several times. Two things a netlist could not keep survive here. The device addresses are parameters, so “no two devices answer to the same address” is a constraint the kernel decides rather than a linter rule. And the RTC’s thresholds are recorded as an assumption, which leaves that link undecided rather than passed.

usb_uart_bridge/ shows part selection landing on the instance rather than the class template. The logical part stays “a 3.3 V regulator”. Which one was bought is a separate, cited fact.

buck_regulator/ puts the reasoning in the graph. The requirement, the part decision, the datasheet numbers behind it, two calculations and the verification that closes the requirement are all entities beside the inductor. fang can answer “why is this 4.7 µH?” without anyone writing a design document.

servo_drive/ is composition at size. A HalfBridge owns its interior: its transistors, its shunt and its own constraints. The drive instantiates three of them from one declaration.