v0.2.9

What's new in 0.2.9

Formula system

• Arbitrary expressions in RHS terms: log(K), I(x^2), log(K):log(L) now work end-to-end
• Interactions between any expressions via : operator
• Readable coefficient names in output (log(K):log(L) instead of __inter_2)

Language

• F-strings parsed at parse-time (zero runtime reparse)
• expr_display covers all AST variants — no more silent _ for valid expressions

Robustness

• Eliminated all unjustified unwrap() calls in interpreter core
• env.rs, post_estimation_ts.rs, estimators_panel.rs, dispatch.rs hardened

Code quality

• exec() decomposed into 7 private methods — from 1366 to ~240 lines
• helpers.rs organised into 9 labelled sections

Validation programme (new)

• ~40 cases validated against R and Python on real datasets (Wooldridge, AER, statsmodels)
• All estimators pass: OLS, WLS, IV, Logit, Probit, Panel FE/RE, Poisson, NegBin, Tobit, Heckman, Cox, Quantile, ARIMA, VAR, VECM, GARCH, DiD, GMM, PSM, RDD, SUR, and more
• hay validate command runs the full programme locally

Dependencies

• Greeners 1.5.4 (preserves column insertion order, fixes get_string for Categorical columns)

What's Changed

• fix: update crossbeam-epoch advisory dependency by @shawcharles in #48
• docs: clarify validation reference semantics by @shawcharles in #46

Full Changelog: v0.2.8...v0.2.9