Update tuple syntax to use {..} instead of (..) and allow named fields

specs/src/lang/language_primitives.md

@@ -149,7 +149,7 @@ TODO
 
 Yurt provides 4 scalar types built-in: Booleans, integers, reals and strings. Yurt also provides tuples as a compound built-int type.
 
-The syntax for a types is as follows:
+The syntax for types is as follows:
 
 ```ebnf
 <ty> ::= "bool"
@@ -158,10 +158,14 @@ The syntax for a types is as follows:
        | "string"
        | <tuple-ty>
 
-<tuple-ty> ::= "(" ( <ty> "," ... ) ")"
+<tuple-ty> ::= "{" ( [ <ident> ":" ] <ty> "," ... ) "}"
 ```
 
-For example, in `let t: (int, real, string) = (5, 3.0, "foo")`, `(int, real, string)` is a tuple type.
+For example, in `let t: { int, real, string } = { 5, 3.0, "foo" }`, `{ int, real, string }` is a tuple type. `{x: int, y: real, string }` is also a tuple tuple type where some of the fields are named.
+
+Names of tuple fields modify the type of the tuple. That is, `{ x: int }` and `{ y: int }` are different types. However they both coerce to `{ int }`.
+
+Note that the grammar disallows empty tuple types `{ }`.
 
 ## Expressions
 
@@ -180,7 +184,7 @@ Expressions represent values and have the following syntax:
          | <real-literal>
          | <string-literal>
          | <tuple-expr>
-         | <tuple-index-expr>
+         | <tuple-field-access-expr>
          | <if-expr>
          | <cond-expr>
          | <call-expr>
@@ -281,23 +285,49 @@ let string = "first line\
              third line";
 ```
 
-#### Tuple Expressions and Tuple Indexing Expressions
+#### Tuple Expressions and Tuple Field Access Expressions
 
 Tuple Expressions are written as:
 
 ```ebnf
-<tuple-expr> ::= "(" ( <expr> "," ... ) ")"
+<tuple-expr> ::= "{" ( [ <ident> ":" ] <expr> "," ... ) "}"
 ```
 
-For example: `let t = (5, 3, "foo");`.
+For example: `let t = { x: 5, 3, "foo" };`. The type of this tuple can be inferred by the compiler to be `{ x: int, int, string }`.
+
+The following is another example:
+
+```rust
+let t: { x: int, real } = { 6, 5.0 }
+```
+
+where the type of the tuple is indicated by the type annotation and has a named field `x`, but that named field is not actually used in the tuple expression. This is allowed because `{ x: int, real }` and `{ int, real }` coerce into each other.
+
+Tuple fields can be initialized out of order only if all the fields have names and their names are used in the tuple expression. For example, the following is allowed:
+
+```rust
+let t: { x: int, y: real } = { y: 5.0, x: 6 };
+```
+
+while the following are not:
+
+```rust
+let t: { x: int, real } = { 5.0, x: 6 };
+let t: { x: int, y: real } = { 5.0, x: 6 };
+let t: { x: int, y: real } = { 5.0, 6 }; // This is a type mismatch!
+```
+
+Tuple expressions that contain a single _unnamed_ field require the trailing `,` as in `let t = { 4.0, };`. Otherwise, the expression becomes a code block that simply evaluates to its contained expression. Tuple expressions that contain a single _named_ field do not require the trailing `,`.
+
+Note that the grammar disallows empty tuple expressions `{ }`.
 
-Tuple indexing expressions are written as:
+Tuple field access expressions are written as:
 
 ```ebnf
-<tuple-index-expr> ::= <expr> "." [0-9]+
+<tuple-field-access-expr> ::= <expr> "." ( [0-9]+ | <ident> )
 ```
 
-For example: `let second = t.1;` which extracts the second element of tuple `t` and stores it into `second`.
+For example: `let second = t.1;` which extracts the second element of tuple `t` and stores it into `second`. Named field can be accessed using their names or their index. For example, if `x` is the third field of tuple `t`, then `t.2` and `t.x` are equivalent.
 
 #### "If" Expressions
 
@@ -349,7 +379,7 @@ The precedence of Yurt operators and expressions is ordered as follows, going fr
 
 | Operator                         | Associativity        |
 | -------------------------------- | -------------------- |
-| Tuple index expressions          | left to right        |
+| Tuple field access expressions   | left to right        |
 | Unary `-`, Unary `+`, `!`        |                      |
 | `*`, `/`, `%`                    | left to right        |
 | Binary `+`, Binary `-`           | left to right        |

yurtc/src/ast.rs

@@ -1,3 +1,5 @@
+use itertools::Either;
+
 #[derive(Clone, Debug, PartialEq)]
 pub(super) enum UseTree {
     Glob,
@@ -46,7 +48,7 @@ pub(super) enum Type {
     Int,
     Bool,
     String,
-    Tuple(Vec<Type>),
+    Tuple(Vec<(Option<Ident>, Type)>),
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -69,10 +71,10 @@ pub(super) enum Expr {
     Block(Block),
     If(IfExpr),
     Cond(CondExpr),
-    Tuple(Vec<Expr>),
-    TupleIndex {
+    Tuple(Vec<(Option<Ident>, Expr)>),
+    TupleFieldAccess {
         tuple: Box<Expr>,
-        index: usize,
+        field: Either<usize, Ident>,
     },
 }
 

yurtc/src/parser.rs

@@ -4,6 +4,7 @@ use crate::{
     lexer::{self, Token, KEYWORDS},
 };
 use chumsky::{prelude::*, Stream};
+use itertools::Either;
 use regex::Regex;
 use std::{fs::read_to_string, path::Path};
 
@@ -278,12 +279,19 @@ fn expr<'sc>() -> impl Parser<Token<'sc>, ast::Expr, Error = ParseError<'sc>> +
             .then(args.clone())
             .map(|(name, args)| ast::Expr::Call { name, args });
 
-        let tuple = args
-            .validate(|args, span, emit| {
-                if args.is_empty() {
+        let tuple_fields = (ident().then_ignore(just(Token::Colon)))
+            .or_not()
+            .then(expr.clone())
+            .separated_by(just(Token::Comma))
+            .allow_trailing()
+            .delimited_by(just(Token::BraceOpen), just(Token::BraceClose));
+
+        let tuple = tuple_fields
+            .validate(|tuple_fields, span, emit| {
+                if tuple_fields.is_empty() {
                     emit(ParseError::EmptyTupleExpr { span })
                 }
-                args
+                tuple_fields
             })
             .map(ast::Expr::Tuple);
 
@@ -304,72 +312,78 @@ fn expr<'sc>() -> impl Parser<Token<'sc>, ast::Expr, Error = ParseError<'sc>> +
             and_or_op(
                 Token::DoubleAmpersand,
                 ast::BinaryOp::LogicalAnd,
-                comparison_op(additive_op(multiplicative_op(tuple_index(atom)))),
+                comparison_op(additive_op(multiplicative_op(tuple_field_access(atom)))),
             ),
         )
     })
 }
 
-fn tuple_index<'sc, P>(
+fn tuple_field_access<'sc, P>(
     parser: P,
 ) -> impl Parser<Token<'sc>, ast::Expr, Error = ParseError<'sc>> + Clone
 where
     P: Parser<Token<'sc>, ast::Expr, Error = ParseError<'sc>> + Clone,
 {
-    let indices =
-        filter_map(|span, token| match &token {
-            Token::IntLiteral(num_str) => num_str
-                .parse::<usize>()
-                .map(|index| vec![index])
-                .map_err(|_| ParseError::InvalidIntegerTupleIndex {
-                    span,
-                    index: num_str,
-                }),
-
-            // If the next token is of the form `<int>.<int>` which, to the lexer, looks like a real,
-            // break it apart manually.
-            Token::RealLiteral(num_str) => {
-                match Regex::new(r"[0-9]+\.[0-9]+")
-                    .expect("valid regex")
-                    .captures(num_str)
-                {
-                    Some(_) => {
-                        // Collect the spans for the two integers
-                        let dot_index = num_str
-                            .chars()
-                            .position(|c| c == '.')
-                            .expect("guaranteed by regex");
-                        let spans = [
-                            span.start..span.start + dot_index,
-                            span.start + dot_index + 1..span.end,
-                        ];
-
-                        // Split at `.` then collect the two indices as `usize`. Report errors as
-                        // needed
-                        num_str
-                            .split('.')
-                            .zip(spans.iter())
-                            .map(|(index, span)| {
-                                index.parse::<usize>().map_err(|_| {
-                                    ParseError::InvalidIntegerTupleIndex {
-                                        span: span.clone(),
-                                        index,
-                                    }
+    let indices = filter_map(|span, token| match &token {
+        // Field access with an identifier
+        Token::Ident(ident) => Ok(vec![Either::Right(ast::Ident(
+            ident.to_owned().to_string(),
+        ))]),
+
+        // Field access with an integer
+        Token::IntLiteral(num_str) => num_str
+            .parse::<usize>()
+            .map(|index| vec![Either::Left(index)])
+            .map_err(|_| ParseError::InvalidIntegerTupleIndex {
+                span,
+                index: num_str,
+            }),
+
+        // If the next token is of the form `<int>.<int>` which, to the lexer, looks like a real,
+        // break it apart manually.
+        Token::RealLiteral(num_str) => {
+            match Regex::new(r"[0-9]+\.[0-9]+")
+                .expect("valid regex")
+                .captures(num_str)
+            {
+                Some(_) => {
+                    // Collect the spans for the two integers
+                    let dot_index = num_str
+                        .chars()
+                        .position(|c| c == '.')
+                        .expect("guaranteed by regex");
+                    let spans = [
+                        span.start..span.start + dot_index,
+                        span.start + dot_index + 1..span.end,
+                    ];
+
+                    // Split at `.` then collect the two indices as `usize`. Report errors as
+                    // needed
+                    num_str
+                        .split('.')
+                        .zip(spans.iter())
+                        .map(|(index, span)| {
+                            index
+                                .parse::<usize>()
+                                .map_err(|_| ParseError::InvalidIntegerTupleIndex {
+                                    span: span.clone(),
+                                    index,
                                 })
-                            })
-                            .collect::<Result<Vec<usize>, _>>()
-                    }
-                    None => Err(ParseError::InvalidTupleIndex { span, index: token }),
+                                .map(Either::Left)
+                        })
+                        .collect::<Result<Vec<Either<usize, ast::Ident>>, _>>()
                 }
+                None => Err(ParseError::InvalidTupleIndex { span, index: token }),
             }
-            _ => Err(ParseError::InvalidTupleIndex { span, index: token }),
-        });
+        }
+        _ => Err(ParseError::InvalidTupleIndex { span, index: token }),
+    });
 
     parser
         .then(just(Token::Dot).ignore_then(indices).repeated().flatten())
-        .foldl(|expr, index| ast::Expr::TupleIndex {
+        .foldl(|expr, field| ast::Expr::TupleFieldAccess {
             tuple: Box::new(expr),
-            index,
+            field,
         })
 }
 
@@ -484,10 +498,12 @@ fn ident<'sc>() -> impl Parser<Token<'sc>, ast::Ident, Error = ParseError<'sc>>
 
 fn type_<'sc>() -> impl Parser<Token<'sc>, ast::Type, Error = ParseError<'sc>> + Clone {
     recursive(|type_| {
-        let tuple = type_
+        let tuple = (ident().then_ignore(just(Token::Colon)))
+            .or_not()
+            .then(type_)
             .separated_by(just(Token::Comma))
             .allow_trailing()
-            .delimited_by(just(Token::ParenOpen), just(Token::ParenClose))
+            .delimited_by(just(Token::BraceOpen), just(Token::BraceClose))
             .validate(|args, span, emit| {
                 if args.is_empty() {
                     emit(ParseError::EmptyTupleType { span })