Keystone for the gene system. A Formula compiles a string from a def
(lexer -> recursive-descent parser -> tree of Func<IFormulaContext,float>)
once, then evaluates allocation-free against a variable context.
Supports + - * / %, comparisons, && || !, ternary, the constants
pi/tau/e, and functions abs sign floor ceil round sqrt exp log sin cos
tan min max pow clamp lerp step. Deterministic and side-effect-free so
gene-effect formulas stay pure. Covered by FormulaTests (parsing,
precedence, functions, logic/ternary, variables, errors).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
