feat: if expressions

crates/lang/src/ast.rs

@@ -437,6 +437,16 @@ pub enum ClauseGuard<Type, RecordTag> {
     Constant(Constant<Type, RecordTag>),
 }
 
+pub type TypedIfBranch = IfBranch<TypedExpr>;
+pub type UntypedIfBranch = IfBranch<UntypedExpr>;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct IfBranch<Expr> {
+    pub condition: Expr,
+    pub body: Expr,
+    pub location: Span,
+}
+
 pub struct TypedRecordUpdateArg {
     pub label: String,
     pub location: Span,

crates/lang/src/expr.rs

@@ -4,8 +4,8 @@ use vec1::Vec1;
 
 use crate::{
     ast::{
-        Annotation, Arg, AssignmentKind, BinOp, CallArg, Clause, Pattern, RecordUpdateSpread, Span,
-        TodoKind, TypedRecordUpdateArg, UntypedRecordUpdateArg,
+        Annotation, Arg, AssignmentKind, BinOp, CallArg, Clause, IfBranch, Pattern,
+        RecordUpdateSpread, Span, TodoKind, TypedRecordUpdateArg, UntypedRecordUpdateArg,
     },
     tipo::{ModuleValueConstructor, PatternConstructor, Type, ValueConstructor},
 };
@@ -104,6 +104,13 @@ pub enum TypedExpr {
         clauses: Vec<Clause<Self, PatternConstructor, Arc<Type>, String>>,
     },
 
+    If {
+        location: Span,
+        branches: Vec1<IfBranch<Self>>,
+        final_else: Box<Self>,
+        tipo: Arc<Type>,
+    },
+
     RecordAccess {
         location: Span,
         tipo: Arc<Type>,
@@ -233,6 +240,12 @@ pub enum UntypedExpr {
         clauses: Vec<Clause<Self, (), (), ()>>,
     },
 
+    If {
+        location: Span,
+        branches: Vec1<IfBranch<Self>>,
+        final_else: Box<Self>,
+    },
+
     FieldAccess {
         location: Span,
         label: String,
@@ -338,7 +351,8 @@ impl UntypedExpr {
             | Self::TupleIndex { location, .. }
             | Self::FieldAccess { location, .. }
             | Self::RecordUpdate { location, .. }
-            | Self::Negate { location, .. } => *location,
+            | Self::Negate { location, .. }
+            | Self::If { location, .. } => *location,
             Self::Sequence {
                 location,
                 expressions,

crates/lang/src/lexer.rs

@@ -25,8 +25,8 @@ pub fn lexer() -> impl Parser<char, Vec<(Token, Span)>, Error = ParseError> {
         just("|>").to(Token::Pipe),
         just(',').to(Token::Comma),
         just(':').to(Token::Colon),
-        just('|').to(Token::Vbar),
         just("||").to(Token::VbarVbar),
+        just('|').to(Token::Vbar),
         just("&&").to(Token::AmperAmper),
     ));
 
@@ -63,6 +63,7 @@ pub fn lexer() -> impl Parser<char, Vec<(Token, Span)>, Error = ParseError> {
         "const" => Token::Const,
         "fn" => Token::Fn,
         "if" => Token::If,
+        "else" => Token::Else,
         "is" => Token::Is,
         "let" => Token::Let,
         "opaque" => Token::Opaque,

crates/lang/src/parser.rs

@@ -443,6 +443,40 @@ pub fn expr_parser(
                 },
             );
 
+        let if_parser = just(Token::If)
+            .ignore_then(r.clone().then(block_parser.clone()).map_with_span(
+                |(condition, body), span| ast::IfBranch {
+                    condition,
+                    body,
+                    location: span,
+                },
+            ))
+            .then(
+                just(Token::Else)
+                    .ignore_then(just(Token::If))
+                    .ignore_then(r.clone().then(block_parser.clone()).map_with_span(
+                        |(condition, body), span| ast::IfBranch {
+                            condition,
+                            body,
+                            location: span,
+                        },
+                    ))
+                    .repeated(),
+            )
+            .then_ignore(just(Token::Else))
+            .then(block_parser.clone())
+            .map_with_span(|((first, alternative_branches), final_else), span| {
+                let mut branches = vec1::vec1![first];
+
+                branches.extend(alternative_branches);
+
+                expr::UntypedExpr::If {
+                    location: span,
+                    branches,
+                    final_else: Box::new(final_else),
+                }
+            });
+
         let expr_unit_parser = choice((
             string_parser,
             int_parser,
@@ -454,6 +488,7 @@ pub fn expr_parser(
             when_parser,
             let_parser,
             assert_parser,
+            if_parser,
         ));
 
         // Parsing a function call into the appropriate structure

crates/lang/src/tests/parser.rs

@@ -93,6 +93,18 @@ fn module() {
             fn update_name(user: User, name: String) -> User {
                 User { ..user, name: "Aiken", }
             }
+
+            fn ifs() {
+                if True {
+                    1 + 1
+                } else if a < 4 {
+                    5
+                } else if a || b {
+                    6
+                } else {
+                    3
+                }
+            }
         "#;
     let len = code.chars().count();
 
@@ -992,6 +1004,81 @@ fn module() {
                     },),
                     return_type: (),
                 },
+                ast::UntypedDefinition::Fn {
+                    arguments: vec![],
+                    body: expr::UntypedExpr::If {
+                        location: Span::new(SrcId::empty(), 1823..2036),
+                        branches: vec1::vec1![
+                            ast::IfBranch {
+                                condition: expr::UntypedExpr::Var {
+                                    location: Span::new(SrcId::empty(), 1826..1830),
+                                    name: "True".to_string(),
+                                },
+                                body: expr::UntypedExpr::BinOp {
+                                    location: Span::new(SrcId::empty(), 1853..1858),
+                                    name: ast::BinOp::AddInt,
+                                    left: Box::new(expr::UntypedExpr::Int {
+                                        location: Span::new(SrcId::empty(), 1853..1854),
+                                        value: "1".to_string(),
+                                    }),
+                                    right: Box::new(expr::UntypedExpr::Int {
+                                        location: Span::new(SrcId::empty(), 1857..1858),
+                                        value: "1".to_string(),
+                                    }),
+                                },
+                                location: Span::new(SrcId::empty(), 1826..1876),
+                            },
+                            ast::IfBranch {
+                                condition: expr::UntypedExpr::BinOp {
+                                    location: Span::new(SrcId::empty(), 1885..1890),
+                                    name: ast::BinOp::LtInt,
+                                    left: Box::new(expr::UntypedExpr::Var {
+                                        location: Span::new(SrcId::empty(), 1885..1886),
+                                        name: "a".to_string(),
+                                    }),
+                                    right: Box::new(expr::UntypedExpr::Int {
+                                        location: Span::new(SrcId::empty(), 1889..1890),
+                                        value: "4".to_string(),
+                                    }),
+                                },
+                                body: expr::UntypedExpr::Int {
+                                    location: Span::new(SrcId::empty(), 1913..1914),
+                                    value: "5".to_string(),
+                                },
+                                location: Span::new(SrcId::empty(), 1885..1932),
+                            },
+                            ast::IfBranch {
+                                condition: expr::UntypedExpr::BinOp {
+                                    location: Span::new(SrcId::empty(), 1941..1947),
+                                    name: ast::BinOp::Or,
+                                    left: Box::new(expr::UntypedExpr::Var {
+                                        location: Span::new(SrcId::empty(), 1941..1942),
+                                        name: "a".to_string(),
+                                    }),
+                                    right: Box::new(expr::UntypedExpr::Var {
+                                        location: Span::new(SrcId::empty(), 1946..1947),
+                                        name: "b".to_string(),
+                                    }),
+                                },
+                                body: expr::UntypedExpr::Int {
+                                    location: Span::new(SrcId::empty(), 1970..1971),
+                                    value: "6".to_string(),
+                                },
+                                location: Span::new(SrcId::empty(), 1941..1989),
+                            },
+                        ],
+                        final_else: Box::new(expr::UntypedExpr::Int {
+                            location: Span::new(SrcId::empty(), 2017..2018),
+                            value: "3".to_string(),
+                        }),
+                    },
+                    doc: None,
+                    location: Span::new(SrcId::empty(), 1796..2050),
+                    name: "ifs".to_string(),
+                    public: false,
+                    return_annotation: None,
+                    return_type: (),
+                },
             ]
         },
     );

crates/lang/src/token.rs

@@ -61,6 +61,7 @@ pub enum Token {
     Const,
     Fn,
     If,
+    Else,
     Is,
     Let,
     Opaque,
@@ -134,6 +135,7 @@ impl fmt::Display for Token {
             Token::Const => "const",
             Token::Fn => "fn",
             Token::If => "if",
+            Token::Else => "else",
             Token::Use => "import",
             Token::Let => "let",
             Token::Opaque => "opaque",