alamb opened a new issue #1718:
URL: https://github.com/apache/arrow-datafusion/issues/1718
**Is your feature request related to a problem or challenge? Please describe
what you are trying to do.**
I am trying to programatically create `Expr`s that represent function calls,
for example `to_timetsamp(x, 4)` or something
To do so today you have to do something like this (from
simplify_expressions.rs) which is 🤮
```rust
// to_timestamp("2020-09-08T12:00:00+00:00")
let expr = Expr::ScalarFunction {
args: vec![lit("2020-09-08T12:00:00+00:00")],
fun: BuiltinScalarFunction::ToTimestamp,
};
```
**Describe the solution you'd like**
I would like to write code like this
```rust
// to_timestamp("2020-09-08T12:00:00+00:00") -->
timestamp(1599566400000000000i64)
let expr = call("to_timestamp",
vec![lit("2020-09-08T12:00:00+00:00")])
.unwrap();
```rust
Perhap with an api like this
```rust
/// Calls a named built in function
///
/// ```
/// use datafusion::logical_plan::*;
///
/// // create the expression sin(x) < 0.2
/// let expr = call("sin", vec![col("x")]).unwrap().lt(lit(0.2));
///
/// ```
pub fn call(name: impl AsRef<str>, args: Vec<Expr>) -> Result<Expr> {
...
}
```
Note you can lookup a `str` to scalar function by name with something like:
```rust
let fun = name.as_ref().parse::<BuiltinScalarFunction>()?;
```
**Additional context**
There are a bunch of this nonsense in `simplify_expression.rs` which could
be cleaned up
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