feat: Allow numeric generics to be referenced and add map (#997)

* Allow numeric generics to be referenced

* Add missed stdlib change

* Declare numeric generics of struct arguments too

* Fix failing test

crates/nargo/tests/test_data/higher-order-functions/src/main.nr

@@ -44,6 +44,8 @@ fn test_array_functions() {
 
     let descending = myarray.sort_via(|a, b| a > b);
     constrain descending == [3, 2, 1];
+
+    constrain evens.map(|n| n / 2) == myarray;
 }
 
 fn foo() -> [u32; 2] {

crates/noirc_frontend/src/hir/resolution/errors.rs

@@ -2,7 +2,7 @@ pub use noirc_errors::Span;
 use noirc_errors::{CustomDiagnostic as Diagnostic, FileDiagnostic};
 use thiserror::Error;
 
-use crate::{Ident, Shared, StructType, Type};
+use crate::{parser::ParserError, Ident, Shared, StructType, Type};
 
 use super::import::PathResolutionError;
 
@@ -59,6 +59,8 @@ pub enum ResolverError {
         actual: usize,
         expected: usize,
     },
+    #[error("{0}")]
+    ParserError(ParserError),
 }
 
 impl ResolverError {
@@ -239,6 +241,7 @@ impl From<ResolverError> for Diagnostic {
                     span,
                 )
             }
+            ResolverError::ParserError(error) => error.into(),
         }
     }
 }

crates/noirc_frontend/src/hir/scope/mod.rs

@@ -137,14 +137,17 @@ impl<K: std::hash::Hash + Eq + Clone, V> ScopeForest<K, V> {
     fn extend_current_scope_tree(&mut self) {
         self.current_scope_tree().push_scope()
     }
+
     fn remove_scope_tree_extension(&mut self) -> Scope<K, V> {
         self.current_scope_tree().pop_scope()
     }
+
     /// Starting a function requires a new scope tree, as you do not want the functions scope to
     /// have access to the scope of the caller
     pub fn start_function(&mut self) {
         self.0.push(ScopeTree::default())
     }
+
     /// Ending a function requires that we removes it's whole tree of scope
     /// This is by design the current scope, which is the last element in the vector
     pub fn end_function(&mut self) -> ScopeTree<K, V> {

crates/noirc_frontend/src/hir/type_check/expr.rs

@@ -3,7 +3,7 @@ use noirc_errors::Span;
 
 use crate::{
     hir_def::{
-        expr::{self, HirBinaryOp, HirExpression, HirLiteral},
+        expr::{self, HirArrayLiteral, HirBinaryOp, HirExpression, HirLiteral},
         types::Type,
     },
     node_interner::{ExprId, FuncId, NodeInterner},
@@ -38,7 +38,7 @@ pub(crate) fn type_check_expression(
         }
         HirExpression::Literal(literal) => {
             match literal {
-                HirLiteral::Array(arr) => {
+                HirLiteral::Array(HirArrayLiteral::Standard(arr)) => {
                     let elem_types =
                         vecmap(&arr, |arg| type_check_expression(interner, arg, errors));
 
@@ -68,6 +68,10 @@ pub(crate) fn type_check_expression(
 
                     arr_type
                 }
+                HirLiteral::Array(HirArrayLiteral::Repeated { repeated_element, length }) => {
+                    let elem_type = type_check_expression(interner, &repeated_element, errors);
+                    Type::Array(Box::new(length), Box::new(elem_type))
+                }
                 HirLiteral::Bool(_) => Type::Bool(CompTime::new(interner)),
                 HirLiteral::Integer(_) => {
                     let id = interner.next_type_variable_id();

crates/noirc_frontend/src/hir_def/expr.rs

@@ -76,12 +76,18 @@ impl HirBinaryOp {
 
 #[derive(Debug, Clone)]
 pub enum HirLiteral {
-    Array(Vec<ExprId>),
+    Array(HirArrayLiteral),
     Bool(bool),
     Integer(FieldElement),
     Str(String),
 }
 
+#[derive(Debug, Clone)]
+pub enum HirArrayLiteral {
+    Standard(Vec<ExprId>),
+    Repeated { repeated_element: ExprId, length: Type },
+}
+
 #[derive(Debug, Clone)]
 pub struct HirPrefixExpression {
     pub operator: UnaryOp,

crates/noirc_frontend/src/hir_def/types.rs

@@ -197,6 +197,14 @@ impl StructType {
         self.fields.keys().cloned().collect()
     }
 
+    /// True if the given index is the same index as a generic type of this struct
+    /// which is expected to be a numeric generic.
+    /// This is needed because we infer type kinds in Noir and don't have extensive kind checking.
+    pub fn generic_is_numeric(&self, index_of_generic: usize) -> bool {
+        let target_id = self.generics[index_of_generic].0;
+        self.fields.iter().any(|(_, field)| field.contains_numeric_typevar(target_id))
+    }
+
     /// Instantiate this struct type, returning a Vec of the new generic args (in
     /// the same order as self.generics)
     pub fn instantiate(&self, interner: &mut NodeInterner) -> Vec<Type> {
@@ -532,6 +540,57 @@ impl Type {
     pub fn is_field(&self) -> bool {
         matches!(self.follow_bindings(), Type::FieldElement(_))
     }
+
+    fn contains_numeric_typevar(&self, target_id: TypeVariableId) -> bool {
+        // True if the given type is a NamedGeneric with the target_id
+        let named_generic_id_matches_target = |typ: &Type| {
+            if let Type::NamedGeneric(type_variable, _) = typ {
+                match &*type_variable.borrow() {
+                    TypeBinding::Bound(_) => {
+                        unreachable!("Named generics should not be bound until monomorphization")
+                    }
+                    TypeBinding::Unbound(id) => target_id == *id,
+                }
+            } else {
+                false
+            }
+        };
+
+        match self {
+            Type::FieldElement(_)
+            | Type::Integer(_, _, _)
+            | Type::Bool(_)
+            | Type::String(_)
+            | Type::Unit
+            | Type::Error
+            | Type::TypeVariable(_)
+            | Type::PolymorphicInteger(_, _)
+            | Type::Constant(_)
+            | Type::NamedGeneric(_, _)
+            | Type::Forall(_, _) => false,
+
+            Type::Array(length, elem) => {
+                elem.contains_numeric_typevar(target_id) || named_generic_id_matches_target(length)
+            }
+
+            Type::Tuple(fields) => {
+                fields.iter().any(|field| field.contains_numeric_typevar(target_id))
+            }
+            Type::Function(parameters, return_type) => {
+                parameters.iter().any(|parameter| parameter.contains_numeric_typevar(target_id))
+                    || return_type.contains_numeric_typevar(target_id)
+            }
+            Type::Struct(struct_type, generics) => {
+                generics.iter().enumerate().any(|(i, generic)| {
+                    if named_generic_id_matches_target(generic) {
+                        struct_type.borrow().generic_is_numeric(i)
+                    } else {
+                        generic.contains_numeric_typevar(target_id)
+                    }
+                })
+            }
+        }
+    }
 }
 
 impl std::fmt::Display for Type {

crates/noirc_frontend/src/monomorphization/mod.rs

@@ -251,11 +251,24 @@ impl<'interner> Monomorphizer<'interner> {
                 let typ = Self::convert_type(&self.interner.id_type(expr));
                 Literal(Integer(value, typ))
             }
-            HirExpression::Literal(HirLiteral::Array(array)) => {
+            HirExpression::Literal(HirLiteral::Array(HirArrayLiteral::Standard(array))) => {
                 let element_type = Self::convert_type(&self.interner.id_type(array[0]));
                 let contents = vecmap(array, |id| self.expr_infer(id));
                 Literal(Array(ast::ArrayLiteral { contents, element_type }))
             }
+            HirExpression::Literal(HirLiteral::Array(HirArrayLiteral::Repeated {
+                repeated_element,
+                length,
+            })) => {
+                let element_type = Self::convert_type(&self.interner.id_type(repeated_element));
+                let contents = self.expr_infer(repeated_element);
+                let length = length
+                    .evaluate_to_u64()
+                    .expect("Length of array is unknown when evaluating numeric generic");
+
+                let contents = vec![contents; length as usize];
+                Literal(Array(ast::ArrayLiteral { contents, element_type }))
+            }
             HirExpression::Block(block) => self.block(block.0),
 
             HirExpression::Prefix(prefix) => ast::Expression::Unary(ast::Unary {
@@ -479,23 +492,36 @@ impl<'interner> Monomorphizer<'interner> {
 
     fn ident(&mut self, ident: HirIdent, expr_id: node_interner::ExprId) -> ast::Expression {
         let definition = self.interner.definition(ident.id);
-        match definition.kind {
+        match &definition.kind {
             DefinitionKind::Function(func_id) => {
                 let mutable = definition.mutable;
                 let location = Some(ident.location);
                 let name = definition.name.clone();
                 let typ = self.interner.id_type(expr_id);
 
-                let definition = self.lookup_function(func_id, expr_id, &typ);
+                let definition = self.lookup_function(*func_id, expr_id, &typ);
                 let typ = Self::convert_type(&typ);
                 let ident = ast::Ident { location, mutable, definition, name, typ };
                 ast::Expression::Ident(ident)
             }
-            DefinitionKind::Global(expr_id) => self.expr_infer(expr_id),
+            DefinitionKind::Global(expr_id) => self.expr_infer(*expr_id),
             DefinitionKind::Local(_) => {
                 let ident = self.local_ident(&ident).unwrap();
                 ast::Expression::Ident(ident)
             }
+            DefinitionKind::GenericType(type_variable) => {
+                let value = match &*type_variable.borrow() {
+                    TypeBinding::Unbound(_) => {
+                        unreachable!("Unbound type variable used in expression")
+                    }
+                    TypeBinding::Bound(binding) => binding.evaluate_to_u64().unwrap_or_else(|| {
+                        panic!("Non-numeric type variable used in expression expecting a value")
+                    }),
+                };
+
+                let value = FieldElement::from(value as u128);
+                ast::Expression::Literal(ast::Literal::Integer(value, ast::Type::Field))
+            }
         }
     }
 

crates/noirc_frontend/src/node_interner.rs

@@ -18,7 +18,7 @@ use crate::hir_def::{
     function::{FuncMeta, HirFunction},
     stmt::HirStatement,
 };
-use crate::{Shared, TypeBinding, TypeBindings, TypeVariableId};
+use crate::{Shared, TypeBinding, TypeBindings, TypeVariable, TypeVariableId};
 
 /// The node interner is the central storage location of all nodes in Noir's Hir (the
 /// various node types can be found in hir_def). The interner is also used to collect
@@ -199,14 +199,18 @@ impl DefinitionInfo {
     }
 }
 
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[derive(Debug, Clone, Eq, PartialEq)]
 pub enum DefinitionKind {
     Function(FuncId),
     Global(ExprId),
 
     /// Locals may be defined in let statements or parameters,
     /// in which case they will not have an associated ExprId
     Local(Option<ExprId>),
+
+    /// Generic types in functions (T, U in `fn foo<T, U>(...)` are declared as variables
+    /// in scope in case they resolve to numeric generics later.
+    GenericType(TypeVariable),
 }
 
 impl DefinitionKind {
@@ -221,6 +225,7 @@ impl DefinitionKind {
             DefinitionKind::Function(_) => None,
             DefinitionKind::Global(id) => Some(id),
             DefinitionKind::Local(id) => id,
+            DefinitionKind::GenericType(_) => None,
         }
     }
 }
@@ -393,13 +398,12 @@ impl NodeInterner {
         mutable: bool,
         definition: DefinitionKind,
     ) -> DefinitionId {
-        let id = self.definitions.len();
-        self.definitions.push(DefinitionInfo { name, mutable, kind: definition });
-
-        let id = DefinitionId(id);
+        let id = DefinitionId(self.definitions.len());
         if let DefinitionKind::Function(func_id) = definition {
             self.function_definition_ids.insert(func_id, id);
         }
+
+        self.definitions.push(DefinitionInfo { name, mutable, kind: definition });
         id
     }
 

noir_stdlib/src/array.nr

@@ -20,6 +20,19 @@ impl<T, N> [T; N] {
         a
     }
 
+    // Apply a function to each element of an array, returning a new array
+    // containing the mapped elements.
+    fn map<U>(self, f: fn(T) -> U) -> [U; N] {
+        let first_elem = f(self[0]);
+        let mut ret = [first_elem; N];
+
+        for i in 1 .. self.len() {
+            ret[i] = f(self[i]);
+        }
+
+        ret
+    }
+
     // Apply a function to each element of the array and an accumulator value,
     // returning the final accumulated value. This function is also sometimes
     // called `foldl`, `fold_left`, `reduce`, or `inject`.