## New syntax

In 0.9.6 we've begun transitioning `jmv` to a new syntax, using tidy evaluation and the use of formulas. Our intention is to do this in a phased way, to minimise disruption and breakage of existing code. Many `jmv` functions now support a `formula =` argument, and this is recommended where applicable. This document describes the changes, and explains how to port existing code to use the new `jmv`. If you've not used `jmv` before, then you don't need to worry about this.

Previously the function `ANOVA` was run:

    jmv::anova(ToothGrowth, 'len', c('supp', 'dose'))

where as the new formula syntax is:

    jmv::ANOVA(formula = len ~ supp * dose, ToothGrowth)

In addition to the new formula syntax, many `jmv` functions support 'non-standard evaluation' of their arguments. For example, the following is now possible:

    jmv::ANOVA(ToothGrowth, len, vars(supp, dose))

(note that, unlike tidy evaluation, a `data` argument is almost always required – we expect to be able to relax this in a future release.)

Additionally, functions which used to accept complex terms arguments, can now use simple formulas. For example, the `emMeans` argument of `ANOVA()` previously required:

    jmv::ANOVA(..., emMeans = list("supp", c("dose", "supp")))

this can now be written:

    jmv::ANOVA(..., emMeans = ~ supp + dose:supp)

In all cases, refer to the examples in the documentation for the recommended syntax. The old syntax (demonstrated above) will continue to be supported into the future.

## Breakage

The new syntax tidies up use of the `jmv` package considerably, but there are a few scenarios where code which used to work, no longer will. The following code will continue to work:

    jmv::ANOVA(ToothGrowth, 'len', c('supp', 'dose'))

However, the following will not:

    dep <- 'len'
    factors <- c('supp', 'dose')

    jmv::ANOVA(ToothGrowth, dep, factors)

In this case, jmv will look for variables in `ToothGrowth` called `'dep'` or `'factors'`. This is tidy evaluation. To instruct `jmv` to use the contents of it's arguments, rather than the symbol name, prefix them with the `!!` signifier. For example:

    dep <- 'len'
    factors <- c('supp', 'dose')

    jmv::ANOVA(ToothGrowth, !!dep, !!factors)