con <- DBI::dbConnect(duckdb())
DBI::dbExecute(con, 'CREATE MACRO eq(a, b) AS a = b')
left <- rel_from_df(con, mtcars)
right <- rel_from_df(con, mtcars)
cond <- list(expr_function("eq", list(expr_reference("cyl", left), expr_reference("cyl", right))))
rel2 <- rel_inner_join(left, right, cond)
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