Add variants

src/eval.rs

@@ -27,11 +27,6 @@ pub fn scoped_eval(expr: Expr, vars: &HashMap<String, Rc<Expr>>) -> Expr {
             } else {
                 // Create a new scope containing the new declaration.
                 let mut new_vars = (*vars).clone();
-                // TODO traverse definition searching for Closure exprs. If we
-                //      find any, traverse their bodies and resolve as many Var
-                //      and Func exprs as we can using current vars map. (If we
-                //      don't find the value in the vars map, np - keep going.)
-                //      In this way, we have inlined "closing over" those vars!
                 new_vars.insert(name, Rc::new(scoped_eval(*definition, vars)));
 
                 // Evaluate in_expr with that new scope's variables.
@@ -39,6 +34,10 @@ pub fn scoped_eval(expr: Expr, vars: &HashMap<String, Rc<Expr>>) -> Expr {
             }
         },
 
+        Let(Variant(name, patterns), definition, in_expr) => {
+            panic!("Pattern matching on variants is not yet supported!");
+        },
+
         Let(Underscore, definition, in_expr) => {
             // Faithfully eval this, but discard its result.
             scoped_eval(*definition, vars);
@@ -56,6 +55,18 @@ pub fn scoped_eval(expr: Expr, vars: &HashMap<String, Rc<Expr>>) -> Expr {
             scoped_eval(Apply(Box::new(func_expr), args), vars)
         },
 
+        ApplyVariant(_, None) => expr, // This is all we do - for now...
+
+        ApplyVariant(name, Some(args)) => {
+            let mut evaluated_args = Vec::with_capacity(args.len());
+
+            for arg in args {
+                evaluated_args.push(scoped_eval(arg, vars))
+            }
+
+            ApplyVariant(name, Some(evaluated_args))
+        }
+
         Apply(func_expr, args) => {
             match *func_expr.clone() {
                 Closure(arg_patterns, body) => {
@@ -69,6 +80,11 @@ pub fn scoped_eval(expr: Expr, vars: &HashMap<String, Rc<Expr>>) -> Expr {
                                 Identifier(name) => {
                                     let new_val = scoped_eval((*args.get(index).unwrap()).clone(), vars);
 
+                                    new_vars.insert(name.clone(), Rc::new(new_val));
+                                }
+                                Variant(name, patterns) => {
+                                    let new_val = scoped_eval((*args.get(index).unwrap()).clone(), vars);
+
                                     new_vars.insert(name.clone(), Rc::new(new_val));
                                 }
                             }

src/expr.rs

@@ -19,6 +19,10 @@ pub enum Expr {
     Operator(Box<Expr>, Operator, Box<Expr>),
     Closure(Vec<Pattern>, Box<Expr>),
 
+    // Sum Types
+    ApplyVariant(String, Option<Vec<Expr>>),
+
+
     If(Box<Expr>, Box<Expr>, Box<Expr>),
     Error(Problem),
 }
@@ -80,6 +84,7 @@ pub enum Problem {
 #[derive(Clone, Debug, PartialEq)]
 pub enum Pattern {
     Identifier(String),
+    Variant(String, Option<Vec<Pattern>>),
     Underscore
 }
 

src/parse.rs

@@ -21,7 +21,6 @@ pub fn parse_string(string: &str) -> Result<Expr, combine::easy::Errors<char, &s
     expr().skip(eof()).easy_parse(parse_state).map(|( expr, _ )| expr)
 }
 
-
 pub fn expr<I>() -> impl Parser<Input = I, Output = Expr>
 where I: Stream<Item = char, Position = IndentablePosition>,
     I::Error: ParseError<I::Item, I::Range, I::Position>
@@ -132,6 +131,7 @@ parser! {
             if_expr(min_indent),
             closure(min_indent),
             let_expr(min_indent),
+            apply_variant(min_indent),
             func_or_var(min_indent),
         ))
     }
@@ -261,7 +261,7 @@ where I: Stream<Item = char, Position = IndentablePosition>,
     I::Error: ParseError<I::Item, I::Range, I::Position>
 {
     attempt(
-        pattern().and(indentation())
+        pattern(min_indent).and(indentation())
             .skip(whitespace())
             .and(
                 char('=').with(indentation())
@@ -313,7 +313,7 @@ where I: Stream<Item = char, Position = IndentablePosition>,
     // TODO patterns must be separated by commas!
     between(char('|'), char('|'),
             sep_by1(
-                pattern(),
+                pattern(min_indent),
                 char(',').skip(indented_whitespaces(min_indent))
             ))
         .and(whitespace1().with(expr_body(min_indent)))
@@ -322,14 +322,69 @@ where I: Stream<Item = char, Position = IndentablePosition>,
         })
 }
 
-pub fn pattern<I>() -> impl Parser<Input = I, Output = Pattern>
+parser! {
+    #[inline(always)]
+    fn pattern[I](min_indent_ref: i32)(I) -> Pattern
+        where [ I: Stream<Item = char, Position = IndentablePosition> ]
+    {
+        let min_indent = *min_indent_ref;
+
+        choice((
+            char('_').map(|_| Pattern::Underscore),
+            ident().map(|name| Pattern::Identifier(name)),
+            match_variant(min_indent)
+        ))
+    }
+}
+
+pub fn apply_variant<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>
 {
-    choice((
-        char('_').map(|_| Pattern::Underscore),
-        ident().map(|name| Pattern::Identifier(name))
-    ))
+    variant_name()
+        .and(optional(attempt(function_application(min_indent))))
+        .map(|(name, opt_args): (String, Option<Vec<Expr>>)|
+            // Use optional(sep_by1()) over sep_by() to avoid
+            // allocating a Vec in case the variant is empty
+            Expr::ApplyVariant(name, opt_args)
+        )
+}
+
+pub fn match_variant<I>(min_indent: i32) -> impl Parser<Input = I, Output = Pattern>
+where I: Stream<Item = char, Position = IndentablePosition>,
+    I::Error: ParseError<I::Item, I::Range, I::Position>
+{
+    variant_name()
+        .and(optional(attempt(
+            sep_by1(
+                pattern(min_indent),
+                char(',').skip(indented_whitespaces(min_indent))
+        ))))
+        .map(|(name, opt_args): (String, Option<Vec<Pattern>>)|
+            // Use optional(sep_by1()) over sep_by() to avoid
+            // allocating a Vec in case the variant is empty
+            Pattern::Variant(name, opt_args)
+        )
+}
+
+
+pub fn variant_name<I>() -> impl Parser<Input = I, Output = String>
+where I: Stream<Item = char, Position = IndentablePosition>,
+    I::Error: ParseError<I::Item, I::Range, I::Position>
+{
+    // Variants must begin with an uppercase letter, but can have any
+    // combination of letters or numbers afterwards.
+    // No underscores, dashes, or apostrophes.
+    many1::<Vec<_>, _>(alpha_num())
+        .then(|chars: Vec<char>| {
+            let valid_start_char = chars[0].is_uppercase();
+
+            if valid_start_char {
+                value(chars.into_iter().collect()).right()
+            } else {
+                unexpected_any("First character in an identifier that was not a lowercase letter").left()
+            }
+        })
 }
 
 pub fn ident<I>() -> impl Parser<Input = I, Output = String>
@@ -342,9 +397,10 @@ where I: Stream<Item = char, Position = IndentablePosition>,
     many1::<Vec<_>, _>(alpha_num())
         .then(|chars: Vec<char>| {
             let valid_start_char = chars[0].is_lowercase();
-            let ident_str:String = chars.into_iter().collect();
 
             if valid_start_char {
+                let ident_str:String = chars.into_iter().collect();
+
                 match ident_str.as_str() {
                     "if" => unexpected_any("Reserved keyword `if`").left(),
                     "then" => unexpected_any("Reserved keyword `then`").left(),