Function datafusion_expr::expr_visitor::inspect_expr_pre

pub fn inspect_expr_pre<F, E>(expr: &Expr, f: F) -> Result<(), E>where
    F: FnMut(&Expr) -> Result<(), E>,

Recursively inspect an Expr and all its childen.

Performs a pre-visit traversal by recursively calling f(expr) on expr, and then on all its children. See ExpressionVisitor for more details and more options to control the walk.