Standard Library

The authoritative release-facing source for the language standard library is the compiler stdlib registry in packages/zplc-compiler/src/compiler/stdlib/index.ts.

That registry is what the IDE/compiler uses to resolve built-in functions and function blocks.

High-value categories

Category	Grounding source	Examples
Timers	stdlib/timers.ts	TON, TOF, TP
Counters	stdlib/counters.ts	CTU, CTD, CTUD
Bistables and triggers	stdlib/bistables.ts	R_TRIG, F_TRIG, RS, SR
System buffers	stdlib/system.ts	FIFO, LIFO
Strings	stdlib/strings.ts	LEN, CONCAT, LEFT, RIGHT, MID, FIND, INSERT, DELETE, REPLACE, STRCMP
Math and logic	stdlib/math.ts, stdlib/functions.ts, stdlib/bitwise.ts	ABS, SQRT, LIMIT, SEL, MUX, SHL, SHR
Process helpers	stdlib/process.ts	HYSTERESIS, DEADBAND, PID_Compact, NORM_X, SCALE_X
Communication FBs	stdlib/communication.ts	MB_READ_HREG, MB_WRITE_COIL, MQTT_CONNECT, MQTT_PUBLISH, MQTT_SUBSCRIBE

Timer and counter blocks

The timer and counter definitions are not just names in a list.

The compiler stdlib files define their member layouts and code-generation behavior, which is why these blocks are safe to document as part of the public language contract.

Examples:

• timers: TON, TOF, TP
• counters: CTU, CTD, CTUD

String functions

The current string surface in stdlib/strings.ts includes:

Function	Description	Example
LEN(STR)	Returns length of string	LEN('ABC') -> 3
LEFT(STR, N)	First N characters	LEFT('HELLO', 2) -> 'HE'
RIGHT(STR, N)	Last N characters	RIGHT('HELLO', 2) -> 'LO'
MID(STR, L, P)	L chars starting at P	MID('HELLO', 2, 2) -> 'EL'
CONCAT(S1, S2)	Join two strings	CONCAT('A', 'B') -> 'AB'
INSERT(S1, S2, P)	Insert S2 into S1 at P	INSERT('AB', 'X', 1) -> 'AXB'
DELETE(S1, L, P)	Delete L chars at P	DELETE('HELLO', 2, 2) -> 'HLO'
REPLACE(S1, S2, L, P)	Replace L chars at P with S2
FIND(S1, S2)	Find position of S2 in S1	FIND('HELLO', 'L') -> 3

Additional utility string functions in the same file include:

• COPY
• CLEAR
• STRCMP
• EQ_STRING
• NE_STRING

Math, logic, and selection functions

Examples directly registered in the stdlib include:

• arithmetic and conversion: ABS, ABSF, NEG, NEGF, MOD, SQRT, EXPT, INT_TO_REAL, REAL_TO_INT
• trigonometry and logs: SIN, COS, TAN, ASIN, ACOS, ATAN, ATAN2, LN, LOG, EXP
• selection helpers: MAX, MIN, LIMIT, SEL, MUX
• bitwise helpers: ROL, ROR, SHL, SHR, AND_WORD, OR_WORD, XOR_WORD, NOT_WORD

Communication function blocks

Communication blocks are part of the compiler stdlib surface too.

The current repo registers blocks such as:

• Modbus: MB_READ_HREG, MB_WRITE_HREG, MB_READ_COIL, MB_WRITE_COIL
• MQTT: MQTT_CONNECT, MQTT_PUBLISH, MQTT_SUBSCRIBE
• cloud wrappers: AZURE_C2D_RECV, AZURE_DPS_PROV, AZURE_EG_PUB, AWS_FLEET_PROV, SPB_REBIRTH

For the runtime-side details and release constraints, continue with:

• Communication Function Blocks
• Connectivity

Practical rule

If a built-in function or block is not registered in the compiler stdlib or justified by the runtime contract, it should not be documented as a firm v1.5 capability.

• CTU: Count Up.
• CTD: Count Down.
• CTUD: Count Up/Down.

Bistables (Flip-Flops)

• SR: Set Dominant (Set takes priority).
• RS: Reset Dominant.

Edge Detection

• R_TRIG: Rising Edge Detector (FALSE -> TRUE).
• F_TRIG: Falling Edge Detector (TRUE -> FALSE).

Control Functions

• PID_Compact: Basic PID controller.
• HYSTERESIS: Two-point controller with deadband.
• LIMIT: Clamp value between Min and Max.
• MUX: Multiplexer (Select one of N inputs).
• SEL: Select one of two inputs.
• MAX, MIN: Maximum/Minimum of two values.

System Functions

• GET_TICKS(): Returns system uptime in milliseconds.
• CYCLE_TIME(): Returns last scan cycle duration in microseconds.