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Structured Text (ST)

Structured Text (ST) is the canonical semantic baseline for ZPLC.

Canonical Role in v1.5​

For v1.5.0:

  • ST is the direct path into the shared compiler backend
  • IL, LD, FBD, and SFC are release-facing workflow paths when they converge into the same backend contract
  • the runtime still executes .zplc, not source-language-specific code

Use the v1.5 Language Suite as the shared parity reference when validating language claims.

Why ST matters architecturally​

packages/zplc-ide/src/compiler/index.ts treats ST differently from the other language paths:

  • ST bypasses the transpilation stage
  • the other languages normalize into ST before compilation

That makes ST the best place to understand the public automation semantics that the runtime is expected to execute.

Typical usage in ZPLC​

ST is the natural fit for:

  • textual control logic
  • arithmetic and data manipulation
  • calling stdlib functions and function blocks directly
  • action bodies that originate from higher-level visual flows

Minimal canonical example​

PROGRAM WorkflowST
VAR
    Start : BOOL := TRUE;
    Timer : TON;
    Out1 : BOOL := FALSE;
END_VAR
Timer(IN := Start, PT := T#250ms);
Out1 := Timer.Q;
END_PROGRAM

What this page should and should not claim​

This page is safe ground for:

  • ST as the direct compiler input path
  • ST as the semantic baseline for the other languages
  • ST examples that match the shared language workflow tests
  • stdlib usage that is backed by the compiler stdlib registry

This page should not pretend ST has special runtime privileges. It compiles into the same bytecode contract as the other language paths.

Common ST building blocks in the current repo​

The compiler and stdlib surfaces show ST being used with:

  • variables and task-oriented program bodies
  • timers such as TON, TOF, and TP
  • counters such as CTU, CTD, and CTUD
  • string functions such as LEN, CONCAT, LEFT, RIGHT, and MID
  • communication FB calls where the runtime/compiler contract supports them

Standard library entry point​

See Standard Library for the built-in functions and function blocks grounded in packages/zplc-compiler/src/compiler/stdlib/index.ts.