added Fn trait

corelib/src/ops.cairo

@@ -15,3 +15,4 @@ use range::RangeOp;
 
 mod function;
 pub use function::FnOnce;
+pub use function::Fn;

corelib/src/ops/function.cairo

@@ -13,3 +13,25 @@ pub trait FnOnce<T, Args> {
     /// Performs the call operation.
     fn call(self: T, args: Args) -> Self::Output;
 }
+
+/// An implementation of `FnOnce` when `Fn` is implemented.
+/// Makes sure we can always pass an `Fn` to a function that expects an `FnOnce`.
+impl FnOnceImpl<T, Args, +Destruct<T>, +Fn<T, Args>> of FnOnce<T, Args> {
+    type Output = Fn::<T, Args>::Output;
+    fn call(self: T, args: Args) -> Self::Output {
+        Fn::call(@self, args)
+    }
+}
+
+/// The version of the call operator that takes a by-snapshot receiver.
+///
+/// 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.
+    type Output;
+    /// Performs the call operation.
+    fn call(self: @T, args: Args) -> Self::Output;
+}

corelib/src/test/language_features/closure_test.cairo

@@ -57,3 +57,15 @@ fn option_map_test() {
     assert_eq!(option_map(Option::Some(2), |x| Option::Some(x)), Option::Some(Option::Some(2)));
 }
 
+fn array_map<T, F, impl Fn: core::ops::Fn<F, (T,)>, +Drop<T>, +Drop<F>, +Drop<Fn::Output>>(
+    arr: [T; 2], f: F,
+) -> [core::ops::Fn::<F, (T,)>::Output; 2] {
+    let [a, b] = arr;
+    [f(a), f(b)]
+}
+
+#[test]
+fn array_map_test() {
+    assert_eq!(array_map([2, 3], |x| x + 3), [5, 6]);
+}
+

crates/cairo-lang-lowering/src/borrow_check/test_data/closure

@@ -272,12 +272,13 @@ blk0 (root):
 Statements:
   (v0: core::felt252) <- 8
   (v1: {[email protected]:3:13: 3:16}) <- struct_construct(v0{`x`})
-  (v2: core::felt252) <- 2
-  (v3: (core::felt252,)) <- struct_construct(v2{`2`})
-  (v4: core::felt252) <- Generated core::ops::function::FnOnce::<{[email protected]:3:13: 3:16}, (core::felt252,)>::call(v1{`c`}, v3{`c(2)`})
-  (v5: core::felt252) <- core::Felt252Add::add(v4{`y`}, v0{`x`})
+  (v2: {[email protected]:3:13: 3:16}, v3: @{[email protected]:3:13: 3:16}) <- snapshot(v1{`c`})
+  (v4: core::felt252) <- 2
+  (v5: (core::felt252,)) <- struct_construct(v4{`2`})
+  (v6: core::felt252) <- Generated core::ops::function::Fn::<{[email protected]:3:13: 3:16}, (core::felt252,)>::call(v3{`c`}, v5{`c(2)`})
+  (v7: core::felt252) <- core::Felt252Add::add(v6{`y`}, v0{`x`})
 End:
-  Return(v5)
+  Return(v7)
 
 //! > ==========================================================================
 
@@ -314,15 +315,16 @@ Statements:
   (v3: core::array::Array::<core::felt252>, v2: ()) <- core::array::ArrayImpl::<core::felt252>::append(v0{`__array_builder_macro_result__`}, v1{`99_felt252`})
   (v4: core::array::Array::<core::felt252>, v5: @core::array::Array::<core::felt252>) <- snapshot(v3{`x`})
   (v6: {[email protected]:3:13: 3:16}) <- struct_construct(v5{`|a| { (@x).len() * (a + 3) }`})
-  (v7: core::integer::u32) <- 2
-  (v8: (core::integer::u32,)) <- struct_construct(v7{`2`})
-  (v9: core::integer::u32) <- Generated core::ops::function::FnOnce::<{[email protected]:3:13: 3:16}, (core::integer::u32,)>::call(v6{`c`}, v8{`c(2)`})
-  (v10: core::array::Array::<core::felt252>, v11: @core::array::Array::<core::felt252>) <- snapshot(v4{`x`})
-  (v12: core::integer::u32) <- 0
-  (v13: @core::felt252) <- core::ops::index::DeprecatedIndexViewImpl::<core::array::Array::<core::felt252>, core::integer::u32, @core::felt252, core::array::ArrayIndex::<core::felt252>>::index(v11{`x`}, v12{`0`})
-  (v14: core::felt252) <- desnap(v13{`0`})
+  (v7: {[email protected]:3:13: 3:16}, v8: @{[email protected]:3:13: 3:16}) <- snapshot(v6{`c`})
+  (v9: core::integer::u32) <- 2
+  (v10: (core::integer::u32,)) <- struct_construct(v9{`2`})
+  (v11: core::integer::u32) <- Generated core::ops::function::Fn::<{[email protected]:3:13: 3:16}, (core::integer::u32,)>::call(v8{`c`}, v10{`c(2)`})
+  (v12: core::array::Array::<core::felt252>, v13: @core::array::Array::<core::felt252>) <- snapshot(v4{`x`})
+  (v14: core::integer::u32) <- 0
+  (v15: @core::felt252) <- core::ops::index::DeprecatedIndexViewImpl::<core::array::Array::<core::felt252>, core::integer::u32, @core::felt252, core::array::ArrayIndex::<core::felt252>>::index(v13{`x`}, v14{`0`})
+  (v16: core::felt252) <- desnap(v15{`0`})
 End:
-  Return(v14)
+  Return(v16)
 
 //! > ==========================================================================
 

crates/cairo-lang-lowering/src/ids.rs

@@ -267,6 +267,7 @@ impl FunctionLongId {
                                 semantic::corelib::destruct_trait_fn(semantic_db),
                                 semantic::corelib::panic_destruct_trait_fn(semantic_db),
                                 semantic::corelib::fn_once_call_trait_fn(semantic_db),
+                                semantic::corelib::fn_call_trait_fn(semantic_db),
                             ]
                             .contains(&function)
                         );

crates/cairo-lang-lowering/src/lower/mod.rs

@@ -1,4 +1,4 @@
-use std::{iter, vec};
+use std::vec;
 
 use block_builder::BlockBuilder;
 use cairo_lang_debug::DebugWithDb;
@@ -7,7 +7,7 @@ use cairo_lang_diagnostics::{Diagnostics, Maybe};
 use cairo_lang_semantic::corelib::{ErrorPropagationType, unwrap_error_propagation_type};
 use cairo_lang_semantic::db::SemanticGroup;
 use cairo_lang_semantic::items::functions::{GenericFunctionId, ImplGenericFunctionId};
-use cairo_lang_semantic::items::imp::{GeneratedImplItems, GeneratedImplLongId, ImplLongId};
+use cairo_lang_semantic::items::imp::ImplLongId;
 use cairo_lang_semantic::usage::MemberPath;
 use cairo_lang_semantic::{
     ConcreteFunction, ConcreteTraitLongId, ExprVar, LocalVariable, VarId, corelib,
@@ -1780,11 +1780,11 @@ fn add_closure_call_function(
     encapsulated_ctx: &mut LoweringContext<'_, '_>,
     expr: &semantic::ExprClosure,
     closure_info: &ClosureInfo,
+    trait_id: cairo_lang_defs::ids::TraitId,
 ) -> Maybe<()> {
-    let semantic_db = encapsulated_ctx.db.upcast();
+    let semantic_db: &dyn SemanticGroup = encapsulated_ctx.db.upcast();
     let closure_ty = extract_matches!(expr.ty.lookup_intern(semantic_db), TypeLongId::Closure);
     let expr_location = encapsulated_ctx.get_location(expr.stable_ptr.untyped());
-    let trait_id = semantic::corelib::fn_once_trait(semantic_db);
     let parameters_ty = TypeLongId::Tuple(closure_ty.param_tys.clone()).intern(semantic_db);
     let concrete_trait = ConcreteTraitLongId {
         trait_id,
@@ -1794,18 +1794,26 @@ fn add_closure_call_function(
         ],
     }
     .intern(semantic_db);
-    let trait_function = semantic::corelib::fn_once_call_trait_fn(semantic_db);
-
-    let ret_ty = semantic_db.trait_type_by_name(trait_id, "Output".into()).unwrap().unwrap();
-    let impl_id = ImplLongId::GeneratedImpl(
-        GeneratedImplLongId {
-            concrete_trait,
-            generic_params: vec![],
-            impl_items: GeneratedImplItems(iter::once((ret_ty, closure_ty.ret_ty)).collect()),
-        }
-        .intern(semantic_db),
-    )
-    .intern(semantic_db);
+    let Ok(impl_id) = semantic::types::get_impl_at_context(
+        semantic_db,
+        encapsulated_ctx.variables.lookup_context.clone(),
+        concrete_trait,
+        None,
+    ) else {
+        // If the impl doesn't exist, there won't be a call to the call-function, so we don't need
+        // to generate it.
+        return Ok(());
+    };
+    if !matches!(impl_id.lookup_intern(semantic_db), ImplLongId::GeneratedImpl(_)) {
+        // If the impl is not generated, we don't need to generate a lowering for it.
+        return Ok(());
+    }
+
+    let trait_function: cairo_lang_defs::ids::TraitFunctionId = semantic_db
+        .trait_function_by_name(trait_id, "call".into())
+        .unwrap()
+        .expect("Call function must exist for an Fn trait.");
+
     let generic_function =
         GenericFunctionId::Impl(ImplGenericFunctionId { impl_id, function: trait_function });
     let function = semantic::FunctionLongId {
@@ -1827,49 +1835,65 @@ fn add_closure_call_function(
     let root_block_id = alloc_empty_block(&mut ctx);
     let mut builder = BlockBuilder::root(&mut ctx, root_block_id);
 
+    let (closure_param_var_id, closure_var) = if trait_id
+        == semantic::corelib::fn_once_trait(semantic_db)
+    {
+        // If the closure is FnOnce, the closure is passed by value.
+        let closure_param_var = ctx.new_var(VarRequest { ty: expr.ty, location: expr_location });
+        let closure_var = VarUsage { var_id: closure_param_var, location: expr_location };
+        (closure_param_var, closure_var)
+    } else {
+        // If the closure is Fn the closure argument will be a snapshot, so we need to desnap it.
+        let closure_param_var = ctx.new_var(VarRequest {
+            ty: wrap_in_snapshots(semantic_db, expr.ty, 1),
+            location: expr_location,
+        });
+
+        let closure_var = generators::Desnap {
+            input: VarUsage { var_id: closure_param_var, location: expr_location },
+            location: expr_location,
+        }
+        .add(&mut ctx, &mut builder.statements);
+        (closure_param_var, closure_var)
+    };
     let parameters: Vec<VariableId> = [
-        ctx.new_var(VarRequest { ty: expr.ty, location: expr_location }),
+        closure_param_var_id,
         ctx.new_var(VarRequest { ty: parameters_ty, location: expr_location }),
     ]
     .into();
-
-    let root_ok = {
-        let captured_vars = generators::StructDestructure {
-            input: VarUsage { var_id: parameters[0], location: expr_location },
-            var_reqs: chain!(closure_info.members.iter(), closure_info.snapshots.iter())
-                .map(|(_, ty)| VarRequest { ty: *ty, location: expr_location })
-                .collect_vec(),
-        }
-        .add(&mut ctx, &mut builder.statements);
-        for (i, (param, _)) in closure_info.members.iter().enumerate() {
-            builder.semantics.introduce(param.clone(), captured_vars[i]);
-        }
-        for (i, (param, _)) in closure_info.snapshots.iter().enumerate() {
-            builder
-                .snapped_semantics
-                .insert(param.clone(), captured_vars[i + closure_info.members.len()]);
-        }
-        let param_vars = generators::StructDestructure {
-            input: VarUsage { var_id: parameters[1], location: expr_location },
-            var_reqs: closure_ty
-                .param_tys
-                .iter()
-                .map(|ty| VarRequest { ty: *ty, location: expr_location })
-                .collect_vec(),
-        }
-        .add(&mut ctx, &mut builder.statements);
-        for (param_var, param) in param_vars.into_iter().zip(expr.params.iter()) {
-            builder
-                .semantics
-                .introduce((&parameter_as_member_path(param.clone())).into(), param_var);
-        }
-        let lowered_expr = lower_expr(&mut ctx, &mut builder, expr.body);
-        let maybe_sealed_block = lowered_expr_to_block_scope_end(&mut ctx, builder, lowered_expr);
-        maybe_sealed_block.and_then(|block_sealed| {
-            wrap_sealed_block_as_function(&mut ctx, block_sealed, expr.stable_ptr.untyped())?;
-            Ok(root_block_id)
-        })
-    };
+    let captured_vars = generators::StructDestructure {
+        input: closure_var,
+        var_reqs: chain!(closure_info.members.iter(), closure_info.snapshots.iter())
+            .map(|(_, ty)| VarRequest { ty: *ty, location: expr_location })
+            .collect_vec(),
+    }
+    .add(&mut ctx, &mut builder.statements);
+    for (i, (param, _)) in closure_info.members.iter().enumerate() {
+        builder.semantics.introduce(param.clone(), captured_vars[i]);
+    }
+    for (i, (param, _)) in closure_info.snapshots.iter().enumerate() {
+        builder
+            .snapped_semantics
+            .insert(param.clone(), captured_vars[i + closure_info.members.len()]);
+    }
+    let param_vars = generators::StructDestructure {
+        input: VarUsage { var_id: parameters[1], location: expr_location },
+        var_reqs: closure_ty
+            .param_tys
+            .iter()
+            .map(|ty| VarRequest { ty: *ty, location: expr_location })
+            .collect_vec(),
+    }
+    .add(&mut ctx, &mut builder.statements);
+    for (param_var, param) in param_vars.into_iter().zip(expr.params.iter()) {
+        builder.semantics.introduce((&parameter_as_member_path(param.clone())).into(), param_var);
+    }
+    let lowered_expr = lower_expr(&mut ctx, &mut builder, expr.body);
+    let maybe_sealed_block = lowered_expr_to_block_scope_end(&mut ctx, builder, lowered_expr);
+    let root_ok = maybe_sealed_block.and_then(|block_sealed| {
+        wrap_sealed_block_as_function(&mut ctx, block_sealed, expr.stable_ptr.untyped())?;
+        Ok(root_block_id)
+    });
     let blocks = root_ok
         .map(|_| ctx.blocks.build().expect("Root block must exist."))
         .unwrap_or_else(FlatBlocks::new_errored);
@@ -1910,8 +1934,20 @@ fn lower_expr_closure(
         ctx,
         expr,
         builder.semantics.closures.get(&capture_var_usage.var_id).unwrap(),
+        semantic::corelib::fn_once_trait(ctx.db.upcast()),
     )
     .map_err(LoweringFlowError::Failed)?;
+
+    if ctx.variables[capture_var_usage.var_id].copyable.is_ok() {
+        add_closure_call_function(
+            ctx,
+            expr,
+            builder.semantics.closures.get(&capture_var_usage.var_id).unwrap(),
+            semantic::corelib::fn_trait(ctx.db.upcast()),
+        )
+        .map_err(LoweringFlowError::Failed)?;
+    }
+
     Ok(closure_variable)
 }
 

crates/cairo-lang-lowering/src/lower/test_data/closure

@@ -277,23 +277,25 @@ End:
   Return()
 
 
-Generated core::ops::function::FnOnce::call lowering for source location:
+Generated core::ops::function::Fn::call lowering for source location:
     let c =  || a;
              ^^
 
-Parameters: v0: {[email protected]:6:14: 6:16}, v1: ()
+Parameters: v0: @{[email protected]:6:14: 6:16}, v2: ()
 blk0 (root):
 Statements:
-  (v2: core::integer::u32) <- struct_destructure(v0)
-  () <- struct_destructure(v1)
+  (v1: {[email protected]:6:14: 6:16}) <- desnap(v0)
+  (v3: core::integer::u32) <- struct_destructure(v1)
+  () <- struct_destructure(v2)
 End:
-  Return(v2)
+  Return(v3)
 
 
 Final lowering:
-Parameters: v0: {[email protected]:6:14: 6:16}, v1: ()
+Parameters: v0: @{[email protected]:6:14: 6:16}, v1: ()
 blk0 (root):
 Statements:
-  (v2: core::integer::u32) <- struct_destructure(v0)
+  (v2: {[email protected]:6:14: 6:16}) <- desnap(v0)
+  (v3: core::integer::u32) <- struct_destructure(v2)
 End:
-  Return(v2)
+  Return(v3)

crates/cairo-lang-semantic/src/corelib.rs

@@ -621,10 +621,22 @@ pub fn fn_once_trait(db: &dyn SemanticGroup) -> TraitId {
     get_core_trait(db, CoreTraitContext::Ops, "FnOnce".into())
 }
 
+pub fn fn_trait(db: &dyn SemanticGroup) -> TraitId {
+    get_core_trait(db, CoreTraitContext::Ops, "Fn".into())
+}
+
+pub fn fn_traits(db: &dyn SemanticGroup) -> [TraitId; 2] {
+    [fn_trait(db), fn_once_trait(db)]
+}
+
 pub fn fn_once_call_trait_fn(db: &dyn SemanticGroup) -> TraitFunctionId {
     get_core_trait_fn(db, CoreTraitContext::Ops, "FnOnce".into(), "call".into())
 }
 
+pub fn fn_call_trait_fn(db: &dyn SemanticGroup) -> TraitFunctionId {
+    get_core_trait_fn(db, CoreTraitContext::Ops, "Fn".into(), "call".into())
+}
+
 pub fn copy_trait(db: &dyn SemanticGroup) -> TraitId {
     get_core_trait(db, CoreTraitContext::TopLevel, "Copy".into())
 }

crates/cairo-lang-semantic/src/diagnostic.rs

@@ -860,8 +860,19 @@ impl DiagnosticEntry for SemanticDiagnostic {
                     )
                 }
             }
-            SemanticDiagnosticKind::TypeEqualTraitReImplementation => {
-                "Type equals trait should not be re-implemented.".into()
+            SemanticDiagnosticKind::CallExpressionRequiresFunction { ty, inference_errors } => {
+                if inference_errors.is_empty() {
+                    format!("Call expression requires a function, found `{}`.", ty.format(db))
+                } else {
+                    format!(
+                        "Call expression requires a function, found `{}`.\n{}",
+                        ty.format(db),
+                        inference_errors.format(db)
+                    )
+                }
+            }
+            SemanticDiagnosticKind::CompilerTraitReImplementation { trait_id } => {
+                format!("Trait `{}` should not be re-implemented.", trait_id.full_path(db.upcast()))
             }
             SemanticDiagnosticKind::ClosureInGlobalScope => {
                 "Closures are not allowed in this context.".into()
@@ -1189,7 +1200,12 @@ pub enum SemanticDiagnosticKind {
         trait_name: SmolStr,
         inference_errors: TraitInferenceErrors,
     },
+    CallExpressionRequiresFunction {
+        ty: semantic::TypeId,
+        inference_errors: TraitInferenceErrors,
+    },
     MultipleImplementationOfIndexOperator(semantic::TypeId),
+
     UnsupportedInlineArguments,
     RedundantInlineAttribute,
     InlineAttrForExternFunctionNotAllowed,
@@ -1231,7 +1247,9 @@ pub enum SemanticDiagnosticKind {
     DerefCycle {
         deref_chain: String,
     },
-    TypeEqualTraitReImplementation,
+    CompilerTraitReImplementation {
+        trait_id: TraitId,
+    },
     ClosureInGlobalScope,
     MaybeMissingColonColon,
     CallingShadowedFunction {