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use super::*;
/// Utility struct for the `when-then-otherwise` expression.
///
/// Represents the state of the expression after [when] is called.
///
/// In this state, `then` must be called to continue to finish the expression.
#[derive(Clone)]
pub struct When {
condition: Expr,
}
/// Utility struct for the `when-then-otherwise` expression.
///
/// Represents the state of the expression after `when(...).then(...)` is called.
#[derive(Clone)]
pub struct Then {
condition: Expr,
statement: Expr,
}
/// Utility struct for the `when-then-otherwise` expression.
///
/// Represents the state of the expression after an additional `when` is called.
///
/// In this state, `then` must be called to continue to finish the expression.
#[derive(Clone)]
pub struct ChainedWhen {
conditions: Vec<Expr>,
statements: Vec<Expr>,
}
/// Utility struct for the `when-then-otherwise` expression.
///
/// Represents the state of the expression after an additional `then` is called.
#[derive(Clone)]
pub struct ChainedThen {
conditions: Vec<Expr>,
statements: Vec<Expr>,
}
impl When {
/// Add a condition to the `when-then-otherwise` expression.
pub fn then<E: Into<Expr>>(self, expr: E) -> Then {
Then {
condition: self.condition,
statement: expr.into(),
}
}
}
impl Then {
/// Attach a statement to the corresponding condition.
pub fn when<E: Into<Expr>>(self, condition: E) -> ChainedWhen {
ChainedWhen {
conditions: vec![self.condition, condition.into()],
statements: vec![self.statement],
}
}
/// Define a default for the `when-then-otherwise` expression.
pub fn otherwise<E: Into<Expr>>(self, statement: E) -> Expr {
ternary_expr(self.condition, self.statement, statement.into())
}
}
impl ChainedWhen {
pub fn then<E: Into<Expr>>(mut self, statement: E) -> ChainedThen {
self.statements.push(statement.into());
ChainedThen {
conditions: self.conditions,
statements: self.statements,
}
}
}
impl ChainedThen {
/// Add another condition to the `when-then-otherwise` expression.
pub fn when<E: Into<Expr>>(mut self, condition: E) -> ChainedWhen {
self.conditions.push(condition.into());
ChainedWhen {
conditions: self.conditions,
statements: self.statements,
}
}
/// Define a default for the `when-then-otherwise` expression.
pub fn otherwise<E: Into<Expr>>(self, expr: E) -> Expr {
// we iterate the preds/ exprs last in first out
// and nest them.
//
// // this expr:
// when((col('x') == 'a')).then(1)
// .when(col('x') == 'b').then(2)
// .when(col('x') == 'c').then(3)
// .otherwise(4)
//
// needs to become:
// when((col('x') == 'a')).then(1) -
// .otherwise( |
// when(col('x') == 'b').then(2) - |
// .otherwise( | |
// pl.when(col('x') == 'c').then(3) | |
// .otherwise(4) | inner | outer
// ) | |
// ) _| _|
//
// by iterating LIFO we first create
// `inner` and then assign that to `otherwise`,
// which will be used in the next layer `outer`
//
let conditions_iter = self.conditions.into_iter().rev();
let mut statements_iter = self.statements.into_iter().rev();
let mut otherwise = expr.into();
for e in conditions_iter {
otherwise = ternary_expr(
e,
statements_iter
.next()
.expect("expr expected, did you call when().then().otherwise?"),
otherwise,
);
}
otherwise
}
}
/// Start a `when-then-otherwise` expression.
pub fn when<E: Into<Expr>>(condition: E) -> When {
When {
condition: condition.into(),
}
}
pub fn ternary_expr(predicate: Expr, truthy: Expr, falsy: Expr) -> Expr {
Expr::Ternary {
predicate: Arc::new(predicate),
truthy: Arc::new(truthy),
falsy: Arc::new(falsy),
}
}
/// Compute `op(l, r)` (or equivalently `l op r`). `l` and `r` must have types compatible with the Operator.
pub fn binary_expr(l: Expr, op: Operator, r: Expr) -> Expr {
Expr::BinaryExpr {
left: Arc::new(l),
op,
right: Arc::new(r),
}
}