SPEC: Control Flow and Variables Syntax

3.6 Assignment Expressions

Statement form:

<lhs> = <expr>

Current lhs support:

R-style variables such as R1

Current expression operands:

numeric literals
variable words such as R2
system variables such as $P_ACT_X

Current system-variable scope:

simple token form such as $P_ACT_X
single-selector form such as $A_IN[1] or $AA_IM[X]
simple and single-selector forms are supported in assignment expressions and control-flow conditions
multi-selector forms such as $P_UIFR[1,X,TR] are deferred

Supported operators:

unary: +, -
binary: +, -, *, /

Parenthesized subexpressions are not supported in v0 expression syntax.

Implemented Siemens baseline checks:

= is required for multi-letter or numeric-extension address values
single-letter plus single-constant omission remains accepted

Planned extension

structured variable references for richer Siemens forms
preserved variable-reference structure in AIL
fuller Siemens expression support

3.7 Control Flow Syntax

Supported goto directions:

GOTOF
GOTOB
GOTO
GOTOC

Supported targets:

labels
block numbers such as N100
numeric targets such as 200
system-variable tokens for runtime indirection

Supported forms:

IF <condition> GOTOx <target>
optional THEN
optional ELSE GOTOx <target>
structured blocks:
- IF ... ELSE ... ENDIF
- WHILE ... ENDWHILE
- FOR ... TO ... ENDFOR
- REPEAT ... UNTIL
- LOOP ... ENDLOOP

Supported condition operators:

==
>
<
>=
<=
<>

Supported logical composition:

AND across condition terms
parenthesized terms are preserved for runtime resolver handling

Notes:

label names follow word-style identifiers and may include underscores
duplicate N line numbers are accepted with warning
parse stage is syntax-first; resolution happens later
AIL preserves simple system-variable references in conditions and goto targets

Example:

N100 G00 X10 Y10
GOTO END_CODE
N110 (This block is skipped)
N120 (This block is skipped)
END_CODE:
N130 G01 X20 Y20