Standard library

Find the modules and built-in functions that every Arc automation can use.

The Arc standard library has modules and built-in functions. To use a module, import it at the top of the file, then call its functions by their qualified name. A qualified name without an import is an error.

import time

time.interval{period=1s} -> heartbeat

Modules

Module	Functions	Use
`control`	`set_authority`	Change control authority while it runs.
`math`	`avg`, `min`, `max`, `derivative`	Get running statistics and rates of change.
`ranges`	`create`, `end`	Mark a period of time as a range.
`stable`	`for`	Pass a value only after it holds steady.
`status`	`set`	Set an alarm, a warning, or a state.
`time`	`interval`, `wait`, `now`	Fire timers and read the time.

Built-in functions

Built-in functions need no import.

Function	Signature	Use
`select`	`bool -> select{} -> (true, false)`	Send each value to a `true` or a `false` routing entry.
`on`	`on{channel} -> T`	Read a channel. Same as a channel name at the start of a flow.
`write`	`T -> write{channel} -> u8`	Write a channel. Same as a channel name at the end of a flow.
`ge`, `gt`, `le`, `lt`, `eq`, `ne`	`T -> gt{b} -> bool`	Compare the input `a` with `b`. Same as `>=`, `>`, `<=`, `<`, `==`, `!=`.
`len`	`len(x) -> i64`	Get the length of a series or a string. Only in a function body.

on and write are the nodes that the graph editor shows as Telemetry source and Telemetry sink. In text, a channel name does the same work:

on{channel=tank_pt} -> tank_pt_copy
tank_pt -> write{channel=tank_pt_copy}

on and write cannot be in the same flow. The compiler cannot find a type for them and stops with on_0_T: unresolved type variable: constraints.

The comparison functions take two numeric values, a and b, of the same type. A flow input fills a, and {} sets b:

tank_pt -> gt{b=300.0} -> tank_high

and, or, and not are keywords, so text code cannot call them as functions. Use the operators.

Deprecated names

The names avg, min, max, derivative, interval, wait, now, set_authority, and stable_for without a module still compile, with warning ARC4003. Use the qualified names, such as math.avg and stable.for.

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