PRD: Variables and Program Structure

5.13 Incremental Parse/Edit-Resume

Primary workflow:

parse and stop at the first failing line under fail-fast policy
edit the failing line
resume from that line while preserving the accepted prefix

Expected session operations:

firstErrorLine()
applyLineEdit(...)
reparseFromLine(...)
reparseFromFirstError()

Requirement:

prefix behavior remains stable
resumed suffix diagnostics and outputs are deterministic

5.14 Variables

Required categories:

user-defined variables such as R1
system variables such as $P_ACT_X
structured system-variable forms such as $A_IN[1] and $P_UIFR[1,X,TR]

Required usage forms:

assignment
expressions
conditions

Behavior boundary:

parse/lowering preserves variable references structurally
runtime resolves values and access policy

Diagnostics must distinguish:

parse-time syntax errors
runtime access/protection failures
runtime pending and unavailable outcomes

Siemens Fundamental NC Syntax Principles

Required coverage:

program naming
block numbering and block length limits
Siemens = rules
comments
skip blocks and skip levels

Behavior boundary:

parse stage recognizes and preserves the structure
runtime decides effective skip behavior

Siemens Subprograms and Call Semantics

Required coverage:

direct subprogram calls by name
repeat counts with P
optional ISO-compat M98
M17 and optional RET
optional future parameterized declaration/call forms

Behavior boundary:

parse/lowering preserves call/declaration structure
runtime resolves targets and manages call stack behavior