Function define_measure 

pub fn define_measure(
    model: &Model,
    text: &str,
    id: u32,
    replace: bool,
) -> Result<Defined>

define, or with replace a redefinition of an existing derived measure: Defined::Unchanged when it parses to the formula it has, else Defined::Replaced. A replacement is refused when its formula would read a measure that depends on the target (a cycle), when it changes the target’s value type while another measure reads it, and when it breaks or reshapes a dependent; each error names the dependent.