Add match keyword

src/eval.rs

@@ -80,13 +80,19 @@ pub fn scoped_eval(expr: Expr, vars: &HashMap<String, Rc<Expr>>) -> Expr {
             }
         },
 
-        Operator(left_arg, op, right_arg) => 
+        Operator(left_arg, op, right_arg) => {
             eval_operator(
                 &scoped_eval(*left_arg, vars),
                 &op,
                 &scoped_eval(*right_arg, vars)
             )
-        ,
+        },
+
+        Match(condition, branches) => {
+            match scoped_eval(*condition, vars) {
+                _ => { panic!("TODO implement eval for match-expressions"); }
+            }
+        },
 
         If(condition, if_true, if_false) => {
             match scoped_eval(*condition, vars) {

src/expr.rs

@@ -22,8 +22,11 @@ pub enum Expr {
     // Sum Types
     ApplyVariant(String, Option<Vec<Expr>>),
 
-
+    // Conditionals
     If(Box<Expr>, Box<Expr>, Box<Expr>),
+    Match(Box<Expr>, Vec<(Pattern, Box<Expr>)>),
+
+    // Error
     Error(Problem),
 }
 

src/parse.rs

@@ -129,6 +129,7 @@ parser! {
             number_literal(),
             char_literal(),
             if_expr(min_indent),
+            match_expr(min_indent),
             closure(min_indent),
             let_expr(min_indent),
             apply_variant(min_indent),
@@ -184,7 +185,7 @@ pub fn if_expr<I>(min_indent: i32) -> impl Parser<Input = I, Output = Expr>
 where I: Stream<Item = char, Position = IndentablePosition>,
     I::Error: ParseError<I::Item, I::Range, I::Position>
 {
-    string("if").with(indented_whitespaces1(min_indent))
+    string("if").skip(indented_whitespaces1(min_indent))
         .with(expr_body(min_indent)).skip(indented_whitespaces1(min_indent))
         .skip(string("then")).skip(indented_whitespaces1(min_indent))
         .and(expr_body(min_indent)).skip(indented_whitespaces1(min_indent))
@@ -199,6 +200,30 @@ where I: Stream<Item = char, Position = IndentablePosition>,
         )
 }
 
+pub fn match_expr<I>(min_indent: i32) -> impl Parser<Input = I, Output = Expr>
+where I: Stream<Item = char, Position = IndentablePosition>,
+    I::Error: ParseError<I::Item, I::Range, I::Position>
+{
+    string("match").skip(indented_whitespaces1(min_indent))
+        .with(expr_body(min_indent)).skip(indented_whitespaces1(min_indent))
+        .and(
+            many::<Vec<_>, _>(
+                string("when").skip(indented_whitespaces1(min_indent))
+                    .with(pattern(min_indent)).skip(indented_whitespaces1(min_indent))
+                    .skip(string("then")).skip(indented_whitespaces1(min_indent))
+                    .and(expr_body(min_indent).map(|expr| Box::new(expr)))
+            )
+        )
+        .map(|(conditional, branches)|
+            if branches.is_empty() {
+                // TODO handle this more gracefully
+                panic!("encountered match-expression with no branches!")
+            } else {
+                Expr::Match(Box::new(conditional), branches)
+            }
+        )
+}
+
 pub fn parenthetical_expr<I>(min_indent: i32) -> impl Parser<Input = I, Output = Expr>
 where I: Stream<Item = char, Position = IndentablePosition>,
     I::Error: ParseError<I::Item, I::Range, I::Position>
@@ -229,7 +254,7 @@ where I: Stream<Item = char, Position = IndentablePosition>,
             sep_by1(
                 attempt(
                     // Keywords like "then" and "else" are not function application!
-                    not_followed_by(choice((string("then"), string("else"))))
+                    not_followed_by(choice((string("then"), string("else"), string("when"))))
                         // Don't parse operators because they have a higher
                         // precedence than function application. If we see one,
                         // we're done!
@@ -404,6 +429,9 @@ where I: Stream<Item = char, Position = IndentablePosition>,
                 match ident_str.as_str() {
                     "if" => unexpected_any("Reserved keyword `if`").left(),
                     "then" => unexpected_any("Reserved keyword `then`").left(),
+                    "else" => unexpected_any("Reserved keyword `else`").left(),
+                    "match" => unexpected_any("Reserved keyword `match`").left(),
+                    "when" => unexpected_any("Reserved keyword `when`").left(),
                     _ => value(ident_str).right()
                 }
             } else {
@@ -561,7 +589,7 @@ where I: Stream<Item = char, Position = IndentablePosition>,
                     char(' ').skip(
                         // Don't mistake keywords like `then` and `else` for
                         // space-separated digits!
-                        not_followed_by(choice((string("then"), string("else"))))
+                        not_followed_by(choice((string("then"), string("else"), string("when"))))
                     )
                 )
         ))