I often find myself yearning for a Rust REPL. I wonder if it'd be possible to run the rust compiler to lower the code down to MIR, and then run that in the Miri interpreter?
If you just want to get the MIR, you can do that today. In the playground, expand the "Run" menu and select "MIR".
The difficulty is more in defining what it means to enter code one line at a time, what about context, scope, lifetimes, all these stuff.
If a more knowledgeable Rust team member can confirm…
e.g.
fn bar(i : &u16) {
i + 1;
}
let a = 8; // a is a u8.
bar(&a); // Now a needs to be a u16,
// but we executed the line of code
// above, which forced it to be u8.
// Is this a type error?
i.e. the above code is entered as:
fn bar(i : &u16) {
i + 1;
}
## Execution happens in the REPL
{
let a = 8;
bar(&a);
}
## Execution happens in the REPL.
In [0] fn bar(i: &u16) { i + 1 }
In [1] let a = 8; // a is a i32.
In [2] bar(&a)
Out[2] Type error: a is a i32 and it needs to be a u16
In [3] let a: u16 = 8; // The original a is shadowed by the new a, the new a is a u16
In [4] bar(&a)
Out[4] 9
Or a similar situation where there isn't enough information to infer a type
In [0] let x = Vec::new();
Out[0] Type error: Need to know the type of x
In [1] let x: Vec<bool> = Vec::new();
In [2] x.push(true); // Note that if we had entered this at the same tiem as Vec::new() the type could have been inferred.
[0] https://play.rust-lang.org/ [1] https://github.com/DanielKeep/cargo-script
https://internals.rust-lang.org/t/pre-rfc-first-class-suppor...