feat: add Expr methods: as_tuple, as_parenthesized, as_index,…

… `as_if` (#5726)

# Description

## Problem

Part of #5668

## Summary

Just four, to keep PRs small.

## Additional Context


## Documentation

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [x] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_frontend/src/hir/comptime/interpreter/builtin.rs

@@ -48,6 +48,9 @@ impl<'local, 'context> Interpreter<'local, 'context> {
             "array_len" => array_len(interner, arguments, location),
             "as_slice" => as_slice(interner, arguments, location),
             "expr_as_function_call" => expr_as_function_call(arguments, return_type, location),
+            "expr_as_if" => expr_as_if(arguments, return_type, location),
+            "expr_as_index" => expr_as_index(arguments, return_type, location),
+            "expr_as_tuple" => expr_as_tuple(arguments, return_type, location),
             "is_unconstrained" => Ok(Value::Bool(true)),
             "function_def_name" => function_def_name(interner, arguments, location),
             "function_def_parameters" => function_def_parameters(interner, arguments, location),
@@ -770,6 +773,71 @@ fn expr_as_function_call(
     })
 }
 
+// fn as_if(self) -> Option<(Expr, Expr, Option<Expr>)>
+fn expr_as_if(
+    arguments: Vec<(Value, Location)>,
+    return_type: Type,
+    location: Location,
+) -> IResult<Value> {
+    expr_as(arguments, return_type.clone(), location, |expr| {
+        if let ExpressionKind::If(if_expr) = expr {
+            // Get the type of `Option<Expr>`
+            let option_type = extract_option_generic_type(return_type.clone());
+            let Type::Tuple(option_types) = option_type else {
+                panic!("Expected the return type option generic arg to be a tuple");
+            };
+            assert_eq!(option_types.len(), 3);
+            let alternative_option_type = option_types[2].clone();
+
+            let alternative =
+                option(alternative_option_type, if_expr.alternative.map(|e| Value::Expr(e.kind)));
+
+            Some(Value::Tuple(vec![
+                Value::Expr(if_expr.condition.kind),
+                Value::Expr(if_expr.consequence.kind),
+                alternative.ok()?,
+            ]))
+        } else {
+            None
+        }
+    })
+}
+
+// fn as_index(self) -> Option<Expr>
+fn expr_as_index(
+    arguments: Vec<(Value, Location)>,
+    return_type: Type,
+    location: Location,
+) -> IResult<Value> {
+    expr_as(arguments, return_type, location, |expr| {
+        if let ExpressionKind::Index(index_expr) = expr {
+            Some(Value::Tuple(vec![
+                Value::Expr(index_expr.collection.kind),
+                Value::Expr(index_expr.index.kind),
+            ]))
+        } else {
+            None
+        }
+    })
+}
+
+// fn as_tuple(self) -> Option<[Expr]>
+fn expr_as_tuple(
+    arguments: Vec<(Value, Location)>,
+    return_type: Type,
+    location: Location,
+) -> IResult<Value> {
+    expr_as(arguments, return_type, location, |expr| {
+        if let ExpressionKind::Tuple(expressions) = expr {
+            let expressions = expressions.into_iter().map(|expr| Value::Expr(expr.kind)).collect();
+            let typ = Type::Slice(Box::new(Type::Quoted(QuotedType::Expr)));
+            Some(Value::Slice(expressions, typ))
+        } else {
+            None
+        }
+    })
+}
+
 // Helper function for implementing the `expr_as_...` functions.
 fn expr_as<F>(
     arguments: Vec<(Value, Location)>,
@@ -781,8 +849,12 @@ where
     F: FnOnce(ExpressionKind) -> Option<Value>,
 {
     let self_argument = check_one_argument(arguments, location)?;
-    let expr = get_expr(self_argument)?;
-    let option_value = f(expr);
+    let mut expression_kind = get_expr(self_argument)?;
+    while let ExpressionKind::Parenthesized(expression) = expression_kind {
+        expression_kind = expression.kind;
+    }
+
+    let option_value = f(expression_kind);
     option(return_type, option_value)
 }
 

noir_stdlib/src/meta/expr.nr

@@ -3,4 +3,13 @@ use crate::option::Option;
 impl Expr {
     #[builtin(expr_as_function_call)]
     fn as_function_call(self) -> Option<(Expr, [Expr])> {}
+
+    #[builtin(expr_as_if)]
+    fn as_if(self) -> Option<(Expr, Expr, Option<Expr>)> {}
+
+    #[builtin(expr_as_index)]
+    fn as_index(self) -> Option<(Expr, Expr)> {}
+
+    #[builtin(expr_as_tuple)]
+    fn as_tuple(self) -> Option<[Expr]> {}
 }

test_programs/compile_success_empty/comptime_exp/src/main.nr

@@ -1,8 +1,31 @@
 fn main() {
     comptime
     {
+        // Check Expr::as_function_call
         let expr = quote { foo(bar) }.as_expr().unwrap();
         let (_function, args) = expr.as_function_call().unwrap();
         assert_eq(args.len(), 1);
+
+        // Check Expr::as_index
+        let expr = quote { foo[bar] }.as_expr().unwrap();
+        let _ = expr.as_index().unwrap();
+
+        // Check Expr::as_tuple
+        let expr = quote { (1, 2) }.as_expr().unwrap();
+        let tuple_exprs = expr.as_tuple().unwrap();
+        assert_eq(tuple_exprs.len(), 2);
+
+        // Check Expr::as_if
+        let expr = quote { if 1 { 2 } }.as_expr().unwrap();
+        let (_condition, _consequence, alternative) = expr.as_if().unwrap();
+        assert(alternative.is_none());
+
+        let expr = quote { if 1 { 2 } else { 3 } }.as_expr().unwrap();
+        let (_condition, _consequence, alternative) = expr.as_if().unwrap();
+        assert(alternative.is_some());
+
+        // Check parenthesized expression is automatically unwrapped
+        let expr = quote { ((if 1 { 2 })) }.as_expr().unwrap();
+        assert(expr.as_if().is_some());
     }
 }