Design of formulas

• simplest mental model
• read [[algebra]]
• all plain attributes (eg, "x") refer to self SO
• dot-prefix (eg, ".x") refers to parent SO
• SO name.attribute name -> reference a non-parent SO (eg, "A.x")
• for attributes with invariant = true -> use default derived formula
  • derived formulas use bare self-refs (eg "X - w")
• empty formula for position attributes -> silently use parent.attribute + value
  • empty formula for length attributes -> silently use value

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Bugs

• 2' resolves to 1' 12"
• value column too narrow, increase by 20px
• values for start in all axes for root MUST ALWAYS be ZERO
• for attributes with formulas, disable the value cell
• stretch a parent -> rotates children (ack!)
• restore on launch also rotates children
• invariant flag ignored during resolve → added enforce_invariants()
• w value shows geometry instead of attribute value → resolve rule: always read .value
• X row shows old user formula after invariant change → set_invariant must clear formula first
• persisted formula on invariant attribute survives reload → rebind_formulas clears invariant formulas at top
• compound imperial .w - 1 1/2" didn't parse → added try_compound_feet/inches to Tokenizer
• algebra fails 1" + 2" -> 1'
• 3' - 1/4" -> does not work in value cells
• display formulas with spaces between tokens (eg. ".l - front_th + dado")

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Examples

For the "x" row:

Formula	Resolves to
(empty)	parent.x_min + x_min
x * 2	self.x_min * 2
.x * 2	parent.x_min * 2
A.x * 2	A.x_min * 2
.x + A.X	parent.x_min + A.x_max

Proposal

Mental model: x means "my own x." .x means "parent's x" (dot-prefix, like A.x with name omitted). Only name another SO when you mean something other than your parent. Empty formula = parent.attribute + value — the default relationship every child already has.

Per architecture, aliases go in Constraints.resolve and .write. Tokenizer, compiler, evaluator stay untouched.

Four changes, in order

1. Alias map in Constraints — resolve_alias(attribute) maps x → x_min, y → y_min, w → computed width, etc. Called inside resolve() before get_bound(). Derived aliases (w, h, d) compute from two bounds (x_max - x_min). Reverse propagation: writing w = 300 sets x_max = x_min + 300.

2. Bare attribute → parent reference — bare identifier like x (no dot) currently throws. Change: bare identifier → reference to parent SO with that attribute. x * 2 tokenizes as { type: 'reference', object: <parent_id>, attribute: 'x' }. Needs parent id passed into tokenizer context or resolved later in Constraints.

3. Empty formula default — when formula is empty/null, Constraints silently treats it as parent.<attribute> + <current_value>. The identity relationship — child at offset from parent.

4. Invariant-derived formulas — when an attribute has invariant = true, it's not a source of truth — it's derived from the other two in its axis. Constraints generates its formula from the alias map's "For Invariant" column: if x is invariant, x → X - w (position derived from far edge minus width). Only one attribute per axis can be invariant. The other two are edited directly; the invariant one recomputes.

Tests

• Alias resolution: x → x_min, X → x_max, w → width
• Bare attribute: x * 2 with parent context → parent.x_min * 2
• Cross-SO reference: A.x * 2 → A.x_min * 2
• WRONG: Empty formula: evaluates to parent.x_min + value
• Reverse propagation through aliases: change result, w updates x_max
• Invariant default: marking x as invariant gives it formula X - w; changing X or w recomputes x
• Only one invariant per axis: marking x invariant means w and X stay editable