added Fn trait

[TomerStarkware]

No description provided.

[reviewable-StarkWare]

This change is 

[orizi]

Reviewed 15 of 16 files at r1.
Reviewable status: 14 of 16 files reviewed, 3 unresolved discussions (waiting on @ilyalesokhin-starkware and @TomerStarkware)

---

crates/cairo-lang-lowering/src/lower/mod.rs line 1949 at r1 (raw file):

        )
        .map_err(LoweringFlowError::Failed)?;
    }

we need both?

Suggestion:

    add_closure_call_function(
        ctx,
        expr,
        builder.semantics.closures.get(&capture_var_usage.var_id).unwrap(),
        if ctx.variables[capture_var_usage.var_id].copyable.is_ok() {
            semantic::corelib::fn_trait(ctx.db.upcast())
        } else {
            semantic::corelib::fn_once_trait(ctx.db.upcast())
        },
    )

---

crates/cairo-lang-semantic/src/items/imp.rs line 1806 at r1 (raw file):

            let ret_ty = db.trait_type_by_name(trait_id, "Output".into()).unwrap().unwrap();

            (

this is very unclear - use the functions properly, even if it means splitting handle_mem_trait into another closure.

---

corelib/src/ops/function.cairo line 33 at r1 (raw file):

pub trait Fn<T, Args> {
    /// The returned type after the call operator is used.

Suggestion:

/// Instances of `Fn` can be called multiple times.
///
/// `Fn` is implemented automatically by closures that capture only copyable variables.
pub trait Fn<T, Args> {
    /// The returned type after the call operator is used.

[TomerStarkware]

Reviewable status: 14 of 16 files reviewed, 3 unresolved discussions (waiting on @ilyalesokhin-starkware and @orizi)

---

crates/cairo-lang-lowering/src/lower/mod.rs line 1949 at r1 (raw file):

Previously, orizi wrote…

we need both?

Done.

---

crates/cairo-lang-semantic/src/items/imp.rs line 1806 at r1 (raw file):

Previously, orizi wrote…

this is very unclear - use the functions properly, even if it means splitting handle_mem_trait into another closure.

Done.

---

corelib/src/ops/function.cairo line 33 at r1 (raw file):

pub trait Fn<T, Args> {
    /// The returned type after the call operator is used.

Done.

[orizi]

Reviewed 3 of 3 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ilyalesokhin-starkware)

[ilyalesokhin-starkware]

Reviewed 7 of 16 files at r1, 1 of 3 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @TomerStarkware)