Semantic: Variables, Control Flow, and Subprogram Validation

Variable and Assignment Validation

Status: Reviewed (2026-03-10 review pass)

Rules to review:

• allowed assignment left-hand sides
• invalid selector forms
• malformed expression structure
• unsupported parenthesized or function-like expression forms
• read-only vs writable variable categories, if enforced before execution

Examples:

• valid: R1 = 2
• valid: R1 = R2 + 1
• invalid: malformed selector syntax

Reviewed decisions:

• valid selector baseline:
  • $NAME[1]
  • $NAME[1,X]
  • $NAME[1,X,TR]
• parenthesized subexpressions are part of the target expression language
• general function-call-style expressions are not part of the baseline expression language for now
• invalid selector baseline:
  • nested brackets
  • quoted-string selector parts
  • arithmetic inside selector parts
  • empty selector parts
  • more than 3 selector parts
  • non-integer first selector part
• invalid expression baseline for now:
  • general function-call-style expressions such as SIN(30) or ABS(R1)

Control-Flow Validation

Status: Reviewed (2026-03-10 review pass)

Rules to review:

• malformed IF/GOTO shapes
• invalid jump target forms
• unsupported condition operators and forms
• duplicate or ambiguous labels / line-number targets
• loop-family parse-only vs executable-lowering diagnostics

Important distinction:

• unresolved forward targets during streaming input are usually execution-time or buffering concerns, not syntax concerns
• malformed target text is still a syntax and semantic issue

Review note:

• family status is reviewed; malformed-shape and invalid-target examples still need to be expanded into explicit accepted and rejected diagnostics

Subprogram Validation

Status: Reviewed (2026-03-10 review pass)

Rules to review:

• malformed PROC declarations
• malformed call shapes
• invalid repeat counts
• ISO-mode gated syntax and validation
• unsupported inline arguments and signatures
• unquoted subprogram names containing characters outside [A-Za-z0-9_] should be rejected with an explicit diagnostic
• block length over 512 characters should be rejected as a validation error

Review note:

• family status is reviewed; ISO-mode gating and repeat-count details still need explicit examples

Comment and Grouping Disambiguation

Status: Reviewed (2026-03-10 review pass)

Rules:

• ; starts comment text to end of line
• parenthesized text after ; is just part of the comment payload
• standalone ( ... ) is not a target comment form
• in expression and condition contexts, ( ... ) is reserved for grouping

Examples:

• valid comment:
  • N0010 ;(CreateDate:Thu Aug 26 08:52:37 2021 by ZK)
• valid grouping intent:
  • IF (R1 == 1) AND (R2 > 10)