conlang: Variable binding and cleanup

ast: Separate concerns, and remove Walk
interpreter: implement variable binding

grammar.ebnf

@@ -16,13 +16,13 @@ Fn          = "fn" Identifier Block ; (* TODO: params, return value*)
 (* # Expressions *)
 (* expression *)
 Expr        = Assign ;
-Block       = '{' Expr '}' ;
+Block       = '{' Stmt* Expr? '}' ;
 Group       = '(' Expr? ')' ;
-Primary     = Item | Identifier | Literal
+Primary     = Identifier | Literal
               | Block | Group | Branch ;
 
 (* expression::math *)
-Assign      = Compare (AssignOp  Compare)* ;
+Assign      = Identifier (AssignOp  Assign) | Compare ;
 Compare     = Range   (CompareOp Range  )* ;
 Range       = Logic   (RangeOp   Logic  )* ;
 Logic       = Bitwise (LogicOp   Bitwise)* ;

libconlang/src/ast.rs

@@ -18,8 +18,8 @@ pub mod preamble {
             math::{self, operator},
         },
         literal,
-        statement::Stmt,
+        statement::*,
-        visitor::{Visitor, Walk},
+        visitor::Visitor,
         Identifier, Program, Start,
     };
 }
@@ -39,7 +39,7 @@ pub struct Program(pub Vec<statement::Stmt>);
 /// An Identifier stores the name of an item
 /// # Syntax
 /// [`Identifier`]` := `[`IDENTIFIER`](crate::token::token_type::Type::Identifier)
-#[derive(Clone, Debug, Hash)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Identifier(pub String);
 
 pub mod todo {
@@ -148,7 +148,12 @@ pub mod statement {
     //! [`Stmt`]` := `[`Let`](Stmt::Let)` | `[`Expr`](Stmt::Expr)
     //! [`Let`](Stmt::Let)` := "let"` [`Identifier`] (`:` `Type`)? (`=` [`Expr`])? `;`
     //! [`Expr`](Stmt::Expr)` := `[`Expr`] `;`
-    use super::{expression::Expr, Identifier};
+    use crate::token::Token;
+
+    use super::{
+        expression::{Block, Expr},
+        Identifier,
+    };
 
     /// Contains a statement
     /// # Syntax
@@ -158,17 +163,31 @@ pub mod statement {
         /// Contains a variable declaration
         /// # Syntax
         /// [`Let`](Stmt::Let) := `"let"` [`Identifier`] (`:` `Type`)? (`=` [`Expr`])? `;`
-        Let {
+        Let(Let),
-            name: Identifier,
-            mutable: bool,
-            ty: Option<Identifier>,
-            init: Option<Expr>,
-        },
         /// Contains an expression statement
         /// # Syntax
         /// [`Expr`](Stmt::Expr) := [`Expr`] `;`
         Expr(Expr),
     }
+
+    /// Contains a variable declaration
+    /// # Syntax
+    /// [`Let`] := `let` [`Identifier`] (`:`) `Type`)? (`=` [`Expr`])? `;`
+    #[derive(Clone, Debug)]
+    pub struct Let {
+        pub name: Identifier,
+        pub mutable: bool,
+        pub ty: Option<Identifier>,
+        pub init: Option<Expr>,
+    }
+
+    #[derive(Clone, Debug)]
+    pub struct Fn {
+        pub name: Identifier,
+        pub args: (), // TODO: capture arguments
+        pub rety: Token,
+        pub body: Block,
+    }
 }
 
 pub mod expression {
@@ -203,14 +222,14 @@ pub mod expression {
     //! `[`Group`]` | `[`control::Flow`]
     //!
     //! See [control] and [math] for their respective production rules.
-    use super::*;
+    use super::{statement::Stmt, *};
 
     /// Contains an expression
     ///
     /// # Syntax
     /// [`Expr`]` := `[`math::Operation`]
     #[derive(Clone, Debug)]
-    pub struct Expr (pub math::Operation);
+    pub struct Expr(pub math::Operation);
 
     /// A [Primary] Expression is the expression with the highest precedence (i.e. the deepest
     /// derivation)
@@ -234,7 +253,8 @@ pub mod expression {
     /// [`Block`] := `'{'` [`Expr`] `'}'`
     #[derive(Clone, Debug)]
     pub struct Block {
-        pub expr: Box<Expr>,
+        pub statements: Vec<Stmt>,
+        pub expr: Option<Box<Expr>>,
     }
 
     /// Contains a Parenthesized Expression
@@ -252,64 +272,83 @@ pub mod expression {
         //! ## Precedence Order
         //! Operator associativity is always left-to-right among members of the same group
         //!
-        //! | # |      Name | Operators                               | Associativity
+        //! | # |       Name | Operators                               | Associativity
-        //! |---|----------:|:----------------------------------------|---------------
+        //! |---|-----------:|:----------------------------------------|---------------
-        //  |   | TODO: Try | `?`                                     |
+        //  |   |  TODO: Try | `?`                                     |
-        //! | 1 |     Unary | [`*` `&` `-` `!`][3]                    | Right
+        //! | 1 |  [Unary][1]| [`*` `&` `-` `!`][4]                    | Right
-        //! | 2 |    Factor | [`*` `/` `%`][4]                        | Left to Right
+        //! | 2 | [Factor][2]| [`*` `/` `%`][5]                        | Left to Right
-        //! | 3 |      Term | [`+` `-`][4]                            | Left to Right
+        //! | 3 |   [Term][2]| [`+` `-`][5]                            | Left to Right
-        //! | 4 |     Shift | [`<<` `>>`][4]                          | Left to Right
+        //! | 4 |  [Shift][2]| [`<<` `>>`][5]                          | Left to Right
-        //! | 5 |   Bitwise | [`&` <code>&#124;</code>][4]            | Left to Right
+        //! | 5 |[Bitwise][2]| [`&` <code>&#124;</code>][4]            | Left to Right
-        //! | 6 |     Logic | [`&&` <code>&#124;&#124;</code> `^^`][4]| Left to Right
+        //! | 6 |  [Logic][2]| [`&&` <code>&#124;&#124;</code> `^^`][5]| Left to Right
-        //! | 7 |   Compare | [`<` `<=` `==` `!=` `>=` `>`][4]        | Left to Right
+        //! | 7 |[Compare][2]| [`<` `<=` `==` `!=` `>=` `>`][5]        | Left to Right
-        #![doc = concat!( //|                                         |
+        #![doc = concat!(  //|                                         |
-        r"  | 8 |    Assign | [`*=`, `/=`, `%=`, `+=`, `-=`, ",     //|
+        r"  | 8 | [Assign][3]| [`*=`, `/=`, `%=`, `+=`, `-=`, ",     //|
-        /*  |   |           |*/ r"`&=`, <code>&#124;=</code>, ",    //|
+        /*  |   |            |*/ r"`&=`, <code>&#124;=</code>, ",    //|
-        /*  |   |           |*/ r"`^=`, `<<=`, `>>=`][4]",          r"| Left to Right")]
+        /*  |   |            |*/ r"`^=`, `<<=`, `>>=`][6]",          r"| Left to Right")]
         //!
         //! <!-- Note: '&#124;' == '|' /-->
         //!
         //! ## Syntax
         //! All precedence levels other than [Unary][1] fold into [Binary][2]
         //!
-        //! [`Assign`][2]`  := `[`Compare`][2]` (`[`AssignOp`][4]`  `[`Compare`][2]`)*`  \
+        //! [`Assign`][3]`  := `[`Compare`][2]` (`[`AssignOp`][6]`  `[`Compare`][2]`)*`  \
-        //! [`Compare`][2]` := `[`Logic`][2]`   (`[`CompareOp`][4]` `[`Logic`][2]`  )*`  \
+        //! [`Compare`][2]` := `[`Logic`][2]`   (`[`CompareOp`][5]` `[`Logic`][2]`  )*`  \
-        //! [`Logic`][2]`   := `[`Bitwise`][2]` (`[`LogicOp`][4]`   `[`Bitwise`][2]`)*`  \
+        //! [`Logic`][2]`   := `[`Bitwise`][2]` (`[`LogicOp`][5]`   `[`Bitwise`][2]`)*`  \
-        //! [`Bitwise`][2]` := `[`Shift`][2]`   (`[`BitwiseOp`][4]` `[`Shift`][2]`  )*`  \
+        //! [`Bitwise`][2]` := `[`Shift`][2]`   (`[`BitwiseOp`][5]` `[`Shift`][2]`  )*`  \
-        //! [`Shift`][2]`   := `[`Term`][2]`    (`[`ShiftOp`][4]`   `[`Term`][2]`   )*`  \
+        //! [`Shift`][2]`   := `[`Term`][2]`    (`[`ShiftOp`][5]`   `[`Term`][2]`   )*`  \
-        //! [`Term`][2]`    := `[`Factor`][2]`  (`[`TermOp`][4]`    `[`Factor`][2]` )*`  \
+        //! [`Term`][2]`    := `[`Factor`][2]`  (`[`TermOp`][5]`    `[`Factor`][2]` )*`  \
-        //! [`Factor`][2]`  := `[`Unary`][1]`   (`[`FactorOp`][4]`  `[`Unary`][1]`  )*`  \
+        //! [`Factor`][2]`  := `[`Unary`][1]`   (`[`FactorOp`][5]`  `[`Unary`][1]`  )*`  \
-        //! [`Unary`][1]`   := (`[`UnaryOp`][3]`)* `[`Primary`]
+        //! [`Unary`][1]`   := (`[`UnaryOp`][4]`)* `[`Primary`]
         //!
         //! [1]: Operation::Unary
         //! [2]: Operation::Binary
-        //! [3]: operator::Unary
+        //! [3]: Operation::Assign
-        //! [4]: operator::Binary
+        //! [4]: operator::Unary
+        //! [5]: operator::Binary
+        //! [6]: operator::Assign
         use super::*;
 
         /// An Operation is a tree of [operands](Primary) and [operators](operator).
         #[derive(Clone, Debug)]
         pub enum Operation {
+            /// [`Assign`](Operation::Assign) :=
+            /// [`Identifier`] [`operator::Assign`] [`Operation`] | [`Operation`]
+            Assign(Assign),
             /// [`Binary`](Operation::Binary) :=
             /// [`Operation`] ([`operator::Binary`] [`Operation`])*
-            Binary {
+            Binary(Binary),
-                first: Box<Self>,
+            /// [`Unary`](Operation::Unary) := ([`operator::Unary`])*
-                other: Vec<(operator::Binary, Self)>,
+            /// [`Primary`](Operation::Primary)
-            },
+            Unary(Unary),
-            /// [`Unary`](Operation::Unary) := ([`operator::Unary`])* [`Primary`]
+            /// [`Primary`](Operation::Primary) := [`expression::Primary`]
-            Unary {
+            Primary(Primary),
-                operators: Vec<operator::Unary>,
-                operand: Primary,
-            },
         }
-        impl Operation {
+
-            pub fn binary(first: Self, other: Vec<(operator::Binary, Self)>) -> Self {
+        /// [`Assign`] := [`Identifier`] [`operator::Assign`] [`Operation`] | [`Operation`]
-                Self::Binary { first: Box::new(first), other }
+        #[derive(Clone, Debug)]
-            }
+        pub struct Assign {
+            pub target: Identifier,
+            pub operator: operator::Assign,
+            pub init: Box<Operation>,
+        }
+
+        /// [`Binary`] := [`Operation`] ([`operator::Binary`] [`Operation`])*
+        #[derive(Clone, Debug)]
+        pub struct Binary {
+            pub first: Box<Operation>,
+            pub other: Vec<(operator::Binary, Operation)>,
+        }
+
+        /// [`Unary`] := ([`operator::Unary`])* [`Primary`](Operation::Primary)
+        #[derive(Clone, Debug)]
+        pub struct Unary {
+            pub operators: Vec<operator::Unary>,
+            pub operand: Box<Operation>,
         }
 
         pub mod operator {
-            //! # [Unary] and [Binary] operators
+            //! # [Unary], [Binary], and [Assign] operators
             //!
             //! An Operator represents the action taken during an [operation](super::Operation)
 
@@ -351,13 +390,6 @@ pub mod expression {
             /// ## Comparison operators
             /// [`<`](Binary::Less), [`<=`](Binary::LessEq), [`==`](Binary::Equal),
             /// [`!=`](Binary::NotEq), [`>=`](Binary::GreaterEq), [`>`](Binary::Greater),
-            /// ## Assignment operators
-            /// [`=`](Binary::Assign), [`+=`](Binary::AddAssign), [`-=`](Binary::SubAssign),
-            /// [`*=`](Binary::MulAssign), [`/=`](Binary::DivAssign), [`%=`](Binary::RemAssign),
-            /// [`&=`](Binary::BitAndAssign), [`|=`](Binary::BitOrAssign),
-            /// [`^=`](Binary::BitXorAssign) [`<<=`](Binary::ShlAssign),
-            /// [`>>=`](Binary::ShrAssign)
-
             #[derive(Clone, Copy, Debug, PartialEq, Eq)]
             pub enum Binary {
                 /// `*`: Multiplication
@@ -402,6 +434,16 @@ pub mod expression {
                 GreaterEq,
                 /// `>`: Greater-than Comparison
                 Greater,
+            }
+
+            /// # Assignment operators
+            /// [`=`](Assign::Assign), [`+=`](Assign::AddAssign), [`-=`](Assign::SubAssign),
+            /// [`*=`](Assign::MulAssign), [`/=`](Assign::DivAssign), [`%=`](Assign::RemAssign),
+            /// [`&=`](Assign::BitAndAssign), [`|=`](Assign::BitOrAssign),
+            /// [`^=`](Assign::BitXorAssign) [`<<=`](Assign::ShlAssign),
+            /// [`>>=`](Assign::ShrAssign)
+            #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+            pub enum Assign {
                 /// `=`: Assignment
                 Assign,
                 /// `+=`: Additive In-place Assignment
@@ -611,182 +653,11 @@ pub mod visitor {
     //! A [`Visitor`] visits every kind of node in the [Abstract Syntax Tree](super). Nodes,
     //! conversely are [`Walkers`](Walk) for Visitors which return a [`Result<(), E>`](Result)
     use super::{
-        expression::{
+        expression::{control::*, math::*, Block, *},
-            control::*,
-            math::{operator::*, *},
-            Block, *,
-        },
         literal::*,
-        statement::Stmt,
+        statement::*,
         *,
     };
-    /// A [Walker](Walk) is a node in the AST, and calls [`Visitor::visit_*()`](Visitor) on all its
-    /// children
-    pub trait Walk<T: Visitor<R> + ?Sized, R> {
-        /// Traverses the children of this node in order, calling the appropriate [Visitor] function
-        fn walk(&self, visitor: &mut T) -> R;
-    }
-    mod walker {
-        use crate::ast::statement::Stmt;
-
-        use super::*;
-        macro leaf($($T:ty),*$(,)?) {$(
-            impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for $T {
-                #[doc = concat!("A(n) [`", stringify!($T), "`] is a leaf node.")]
-                /// Calling this will do nothing.
-                fn walk(&self, _visitor: &mut T) -> Result<(), E> { Ok(()) }
-            }
-        )*}
-        leaf!(Binary, bool, char, Continue, Float, Identifier, str, u128, Unary);
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for While {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_expr(&self.cond)?;
-                visitor.visit_block(&self.body)?;
-                match &self.else_ {
-                    Some(expr) => visitor.visit_else(expr),
-                    None => Ok(()),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for If {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_expr(&self.cond)?;
-                visitor.visit_block(&self.body)?;
-                match &self.else_ {
-                    Some(expr) => visitor.visit_else(expr),
-                    None => Ok(()),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for For {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_identifier(&self.var)?;
-                visitor.visit_expr(&self.iter)?;
-                visitor.visit_block(&self.body)?;
-                match &self.else_ {
-                    Some(expr) => visitor.visit_else(expr),
-                    None => Ok(()),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Else {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_block(&self.block)
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Return {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_expr(&self.expr)
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Break {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_expr(&self.expr)
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Start {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_program(&self.0)
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Expr {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_operation(&self.0)
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Group {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                match self {
-                    Group::Expr(expr) => visitor.visit_expr(expr),
-                    Group::Empty => visitor.visit_empty(),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Block {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                visitor.visit_expr(&self.expr)
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Operation {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                match self {
-                    Operation::Binary { first, other } => {
-                        visitor.visit_operation(first)?;
-                        for (op, other) in other {
-                            visitor.visit_binary_op(op)?;
-                            visitor.visit_operation(other)?;
-                        }
-                        Ok(())
-                    }
-                    Operation::Unary { operators, operand } => {
-                        for op in operators {
-                            visitor.visit_unary_op(op)?;
-                        }
-                        visitor.visit_primary(operand)
-                    }
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Primary {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                match self {
-                    Primary::Identifier(i) => visitor.visit_identifier(i),
-                    Primary::Literal(l) => visitor.visit_literal(l),
-                    Primary::Block(b) => visitor.visit_block(b),
-                    Primary::Group(g) => visitor.visit_group(g),
-                    Primary::Branch(b) => visitor.visit_branch_expr(b),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Literal {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                match self {
-                    Literal::String(s) => visitor.visit_string_literal(s),
-                    Literal::Char(c) => visitor.visit_char_literal(c),
-                    Literal::Bool(b) => visitor.visit_bool_literal(b),
-                    Literal::Float(f) => visitor.visit_float_literal(f),
-                    Literal::Int(i) => visitor.visit_int_literal(i),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Flow {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                match self {
-                    Flow::While(w) => visitor.visit_while(w),
-                    Flow::If(i) => visitor.visit_if(i),
-                    Flow::For(f) => visitor.visit_for(f),
-                    Flow::Continue(c) => visitor.visit_continue(c),
-                    Flow::Return(r) => visitor.visit_return(r),
-                    Flow::Break(b) => visitor.visit_break(b),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Stmt {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                match self {
-                    Stmt::Let { name, mutable: _, ty, init } => {
-                        visitor.visit_identifier(name)?;
-                        if let Some(ty) = ty {
-                            visitor.visit_identifier(ty)?;
-                        }
-                        if let Some(init) = init {
-                            visitor.visit_expr(init)?;
-                        }
-                        Ok(())
-                    }
-                    Stmt::Expr(e) => visitor.visit_expr(e),
-                }
-            }
-        }
-        impl<T: Visitor<Result<(), E>> + ?Sized, E> Walk<T, Result<(), E>> for Program {
-            fn walk(&self, visitor: &mut T) -> Result<(), E> {
-                for stmt in &self.0 {
-                    visitor.visit_statement(stmt)?;
-                }
-                Ok(())
-            }
-        }
-    }
 
     /// A Visitor traverses every kind of node in the [Abstract Syntax Tree](super)
     pub trait Visitor<R> {
@@ -798,7 +669,14 @@ pub mod visitor {
         fn visit_program(&mut self, prog: &Program) -> R;
 
         /// Visit a [Statement](Stmt)
-        fn visit_statement(&mut self, stmt: &Stmt) -> R;
+        fn visit_statement(&mut self, stmt: &Stmt) -> R {
+            match stmt {
+                Stmt::Let(stmt) => self.visit_let(stmt),
+                Stmt::Expr(expr) => self.visit_expr(expr),
+            }
+        }
+        /// Visit a [Let statement](Let)
+        fn visit_let(&mut self, stmt: &Let) -> R;
 
         /// Visit an [Expression](Expr)
         fn visit_expr(&mut self, expr: &Expr) -> R {
@@ -806,9 +684,7 @@ pub mod visitor {
         }
         // Block expression
         /// Visit a [Block] expression
-        fn visit_block(&mut self, expr: &Block) -> R {
+        fn visit_block(&mut self, block: &Block) -> R;
-            self.visit_expr(&expr.expr)
-        }
         /// Visit a [Group] expression
         fn visit_group(&mut self, group: &Group) -> R {
             match group {
@@ -819,9 +695,23 @@ pub mod visitor {
 
         // Math expression
         /// Visit an [Operation]
-        fn visit_operation(&mut self, expr: &Operation) -> R;
+        fn visit_operation(&mut self, operation: &Operation) -> R {
-        /// Visit a [Binary](Operation::Binary) [operator](operator::Binary)
+            match operation {
+                Operation::Assign(assign) => self.visit_assign(assign),
+                Operation::Binary(binary) => self.visit_binary(binary),
+                Operation::Unary(unary) => self.visit_unary(unary),
+                Operation::Primary(primary) => self.visit_primary(primary),
+            }
+        }
+        /// Visit an [Assignment](Assign) operation
+        fn visit_assign(&mut self, assign: &Assign) -> R;
+        /// Visit a [Binary] Operation
+        fn visit_binary(&mut self, binary: &Binary) -> R;
+        /// Visit a [Unary] Operation
+        fn visit_unary(&mut self, unary: &Unary) -> R;
         // Math operators
+        fn visit_assign_op(&mut self, op: &operator::Assign) -> R;
+        /// Visit a [Binary](Operation::Binary) [operator](operator::Binary)
         fn visit_binary_op(&mut self, op: &operator::Binary) -> R;
         /// Visit a [Unary](Operation::Unary) [operator](operator::Unary)
         fn visit_unary_op(&mut self, op: &operator::Unary) -> R;
@@ -829,8 +719,8 @@ pub mod visitor {
         /// Visit a [Primary] expression
         ///
         /// [`Primary`]` := `[`Identifier`]` | `[`Literal`]` | `[`Block`]` | `[`Flow`]
-        fn visit_primary(&mut self, expr: &Primary) -> R {
+        fn visit_primary(&mut self, primary: &Primary) -> R {
-            match expr {
+            match primary {
                 Primary::Identifier(v) => self.visit_identifier(v),
                 Primary::Literal(v) => self.visit_literal(v),
                 Primary::Block(v) => self.visit_block(v),

libconlang/src/interpreter.rs

@@ -1,5 +1,6 @@
 //! Interprets an AST as a program
 
+use self::scope::Environment;
 use crate::ast::preamble::*;
 use error::{Error, IResult, Reason};
 use temp_type_impl::ConValue;
@@ -12,9 +13,10 @@ pub mod temp_type_impl {
     ///
     /// This is a hack to work around the fact that Conlang doesn't have a functioning type system
     /// yet :(
-    #[derive(Clone, Debug)]
+    #[derive(Clone, Debug, Default)]
     pub enum ConValue {
         /// The empty/unit `()` type
+        #[default]
         Empty,
         /// An integer
         Int(i128),
@@ -57,6 +59,18 @@ pub mod temp_type_impl {
             gt_eq: true, >=;
             gt: false, >;
         }
+        assign! {
+            add_assign: +;
+            bitand_assign: &;
+            bitor_assign: |;
+            bitxor_assign: ^;
+            div_assign: /;
+            mul_assign: *;
+            rem_assign: %;
+            shl_assign: <<;
+            shr_assign: >>;
+            sub_assign: -;
+        }
     }
     /// Templates comparison functions for [ConValue]
     macro cmp ($($fn:ident: $empty:literal, $op:tt);*$(;)?) {$(
@@ -73,6 +87,12 @@ pub mod temp_type_impl {
             }
         }
     )*}
+    macro assign($( $fn: ident: $op: tt );*$(;)?) {$(
+        pub fn $fn(&mut self, other: Self) -> IResult<()> {
+            *self = (std::mem::take(self) $op other)?;
+            Ok(())
+        }
+    )*}
     /// Implements [From] for an enum with 1-tuple variants
     macro from ($($T:ty => $v:expr),*$(,)?) {
         $(impl From<$T> for ConValue {
@@ -197,6 +217,7 @@ pub mod temp_type_impl {
 /// A work-in-progress tree walk interpreter for Conlang
 #[derive(Clone, Debug, Default)]
 pub struct Interpreter {
+    scope: Box<Environment>,
     stack: Vec<ConValue>,
 }
 
@@ -230,6 +251,13 @@ impl Interpreter {
     fn pop_two(&mut self) -> IResult<(ConValue, ConValue)> {
         Ok((self.pop()?, self.pop()?))
     }
+    fn resolve(&mut self, value: &Identifier) -> IResult<ConValue> {
+        self.scope
+            .get(value)
+            .cloned()
+            .ok_or_else(|| Error::with_reason(Reason::NotDefined(value.to_owned())))?
+            .ok_or_else(|| Error::with_reason(Reason::NotInitialized(value.to_owned())))
+    }
 }
 
 impl Visitor<IResult<()>> for Interpreter {
@@ -242,10 +270,7 @@ impl Visitor<IResult<()>> for Interpreter {
 
     fn visit_statement(&mut self, stmt: &Stmt) -> IResult<()> {
         match stmt {
-            Stmt::Let { name, mutable, ty, init } => todo!(
+            Stmt::Let(l) => self.visit_let(l),
-                "let{} {name:?}: {ty:?} = {init:?}",
-                if *mutable { " mut" } else { "" }
-            ),
             Stmt::Expr(e) => {
                 self.visit_expr(e)?;
                 self.pop().map(drop)
@@ -253,57 +278,124 @@ impl Visitor<IResult<()>> for Interpreter {
         }
     }
 
-    fn visit_operation(&mut self, expr: &math::Operation) -> IResult<()> {
+    fn visit_let(&mut self, stmt: &Let) -> IResult<()> {
-        use math::Operation;
+        let Let { name, init, .. } = stmt;
-        // TODO: the indentation depth here is driving me insane.
+        if let Some(init) = init {
-        //       maybe refactor the ast to break binary and unary
+            self.visit_expr(init)?;
-        //       operations into their own nodes, and use
+            let init = self.pop()?;
-        //       Operation to unify them?
+            self.scope.insert(name, Some(init));
-        match expr {
+        } else {
-            Operation::Binary { first, other } => {
+            self.scope.insert(name, None);
-                self.visit_operation(first)?;
+        }
-                for (op, other) in other {
+        Ok(())
-                    match op {
+    }
-                        operator::Binary::LogAnd => {
+
-                            if self.peek()?.truthy()? {
+    fn visit_block(&mut self, block: &expression::Block) -> IResult<()> {
-                                self.pop()?;
+        for stmt in &block.statements {
-                                self.visit_operation(other)?;
+            self.visit_statement(stmt)?;
-                            }
+        }
-                        }
+        if let Some(expr) = block.expr.as_ref() {
-                        operator::Binary::LogOr => {
+            self.visit_expr(expr)
-                            if !self.peek()?.truthy()? {
+        } else {
-                                self.pop()?;
+            self.push(ConValue::Empty);
-                                self.visit_operation(other)?;
+            Ok(())
-                            }
+        }
-                        }
+    }
-                        operator::Binary::LogXor => {
+
-                            let first = self.pop()?.truthy()?;
+    fn visit_assign(&mut self, assign: &math::Assign) -> IResult<()> {
-                            self.visit_operation(other)?;
+        use operator::Assign;
-                            let second = self.pop()?.truthy()?;
+        let math::Assign { target, operator, init } = assign;
-                            self.push(first ^ second);
+        self.visit_operation(init)?;
-                        }
+        let init = self.pop()?;
-                        _ => {
+        let Some(resolved) = self.scope.get_mut(target) else {
-                            self.visit_operation(other)?;
+            Err(Error::with_reason(Reason::NotDefined(target.to_owned())))?
-                            self.visit_binary_op(op)?;
+        };
-                        }
+        if let Assign::Assign = operator {
+            use std::mem::discriminant as variant;
+            // runtime typecheck
+            match resolved.as_mut() {
+                Some(value) if variant(value) == variant(&init) => {
+                    *value = init;
+                }
+                None => *resolved = Some(init),
+                _ => Err(Error::with_reason(Reason::TypeError))?,
+            }
+            self.push(ConValue::Empty);
+            return Ok(());
+        }
+        let Some(target) = resolved.as_mut() else {
+            Err(Error::with_reason(Reason::NotInitialized(
+                target.to_owned(),
+            )))?
+        };
+        match operator {
+            Assign::AddAssign => target.add_assign(init)?,
+            Assign::SubAssign => target.sub_assign(init)?,
+            Assign::MulAssign => target.mul_assign(init)?,
+            Assign::DivAssign => target.div_assign(init)?,
+            Assign::RemAssign => target.rem_assign(init)?,
+            Assign::BitAndAssign => target.bitand_assign(init)?,
+            Assign::BitOrAssign => target.bitor_assign(init)?,
+            Assign::BitXorAssign => target.bitxor_assign(init)?,
+            Assign::ShlAssign => target.shl_assign(init)?,
+            Assign::ShrAssign => target.shr_assign(init)?,
+            _ => (),
+        }
+        self.push(ConValue::Empty);
+        Ok(())
+    }
+
+    fn visit_binary(&mut self, bin: &math::Binary) -> IResult<()> {
+        use math::Binary;
+        let Binary { first, other } = bin;
+
+        self.visit_operation(first)?;
+        for (op, other) in other {
+            match op {
+                operator::Binary::LogAnd => {
+                    if self.peek()?.truthy()? {
+                        self.pop()?;
+                        self.visit_operation(other)?;
                     }
                 }
-                Ok(())
+                operator::Binary::LogOr => {
-            }
+                    if !self.peek()?.truthy()? {
-            Operation::Unary { operators, operand } => {
+                        self.pop()?;
-                self.visit_primary(operand)?;
+                        self.visit_operation(other)?;
-                for op in operators.iter().rev() {
+                    }
-                    self.visit_unary_op(op)?;
+                }
+                operator::Binary::LogXor => {
+                    let first = self.pop()?.truthy()?;
+                    self.visit_operation(other)?;
+                    let second = self.pop()?.truthy()?;
+                    self.push(first ^ second);
+                }
+                _ => {
+                    self.visit_operation(other)?;
+                    self.visit_binary_op(op)?;
                 }
-                Ok(())
             }
         }
+        Ok(())
+    }
+
+    fn visit_unary(&mut self, unary: &math::Unary) -> IResult<()> {
+        let math::Unary { operand, operators } = unary;
+        self.visit_operation(operand)?;
+        for op in operators.iter().rev() {
+            self.visit_unary_op(op)?;
+        }
+        Ok(())
+    }
+
+    fn visit_assign_op(&mut self, _: &operator::Assign) -> IResult<()> {
+        unimplemented!("visit_assign_op is implemented in visit_operation")
     }
 
     fn visit_binary_op(&mut self, op: &operator::Binary) -> IResult<()> {
         use operator::Binary;
         let (second, first) = self.pop_two()?;
-        self.push(match op {
+        let out = match op {
             Binary::Mul => first * second,
             Binary::Div => first / second,
             Binary::Rem => first % second,
@@ -325,18 +417,8 @@ impl Visitor<IResult<()>> for Interpreter {
             Binary::NotEq => first.neq(&second),
             Binary::GreaterEq => first.gt_eq(&second),
             Binary::Greater => first.gt(&second),
-            Binary::Assign => todo!("Assignment"),
+        }?;
-            Binary::AddAssign => todo!("Assignment"),
+        self.push(out);
-            Binary::SubAssign => todo!("Assignment"),
-            Binary::MulAssign => todo!("Assignment"),
-            Binary::DivAssign => todo!("Assignment"),
-            Binary::RemAssign => todo!("Assignment"),
-            Binary::BitAndAssign => todo!("Assignment"),
-            Binary::BitOrAssign => todo!("Assignment"),
-            Binary::BitXorAssign => todo!("Assignment"),
-            Binary::ShlAssign => todo!("Assignment"),
-            Binary::ShrAssign => todo!("Assignment"),
-        }?);
         Ok(())
     }
 
@@ -364,12 +446,13 @@ impl Visitor<IResult<()>> for Interpreter {
             self.visit_block(&expr.body)?;
         } else if let Some(block) = &expr.else_ {
             self.visit_else(block)?;
+        } else {
+            self.push(ConValue::Empty)
         }
         Ok(())
     }
 
     fn visit_while(&mut self, expr: &control::While) -> IResult<()> {
-        let mut broke = false;
         while {
             self.visit_expr(&expr.cond)?;
             self.pop()?.truthy()?
@@ -384,26 +467,28 @@ impl Visitor<IResult<()>> for Interpreter {
                 Reason::Continue => continue,
                 Reason::Break(value) => {
                     self.push(value);
-                    broke = true;
+                    return Ok(());
-                    break;
                 }
                 r => Err(Error::with_reason(r))?,
             }
         }
-        if let (Some(r#else), false) = (&expr.else_, broke) {
+        if let Some(r#else) = &expr.else_ {
             self.visit_else(r#else)?;
+        } else {
+            self.push(ConValue::Empty);
         }
         Ok(())
     }
 
     fn visit_for(&mut self, expr: &control::For) -> IResult<()> {
+        self.scope.enter();
         self.visit_expr(&expr.iter)?;
-        let mut broke = false;
         let bounds = match self.pop()? {
             ConValue::RangeExc(a, b) | ConValue::RangeInc(a, b) => (a, b),
             _ => Err(Error::with_reason(Reason::NotIterable))?,
         };
-        for _ in bounds.0..=bounds.1 {
+        for loop_var in bounds.0..=bounds.1 {
+            self.scope.insert(&expr.var, Some(loop_var.into()));
             let Err(out) = self.visit_block(&expr.body) else {
                 self.pop()?;
                 continue;
@@ -412,15 +497,17 @@ impl Visitor<IResult<()>> for Interpreter {
                 Reason::Continue => continue,
                 Reason::Break(value) => {
                     self.push(value);
-                    broke = true;
+                    return Ok(());
-                    break;
                 }
                 r => Err(Error::with_reason(r))?,
             }
         }
-        if let (Some(r#else), false) = (&expr.else_, broke) {
+        if let Some(r#else) = &expr.else_ {
             self.visit_else(r#else)?;
+        } else {
+            self.push(ConValue::Empty)
         }
+        self.scope.exit()?;
         Ok(())
     }
 
@@ -447,7 +534,9 @@ impl Visitor<IResult<()>> for Interpreter {
     }
 
     fn visit_identifier(&mut self, ident: &Identifier) -> IResult<()> {
-        todo!("Identifier lookup and scoping rules: {ident:?}")
+        let value = self.resolve(ident)?;
+        self.push(value);
+        Ok(())
     }
 
     fn visit_string_literal(&mut self, string: &str) -> IResult<()> {
@@ -480,8 +569,69 @@ impl Visitor<IResult<()>> for Interpreter {
     }
 }
 
+pub mod scope {
+    //! Lexical and non-lexical scoping for variables
+    use super::{
+        error::{Error, IResult, Reason},
+        temp_type_impl::ConValue,
+        Identifier,
+    };
+    use std::collections::HashMap;
+
+    #[derive(Clone, Debug, Default)]
+    pub enum Variable {
+        #[default]
+        Uninit,
+        Init(ConValue),
+    }
+
+    /// Implements a nested lexical scope
+    #[derive(Clone, Debug, Default)]
+    pub struct Environment {
+        outer: Option<Box<Self>>,
+        vars: HashMap<Identifier, Option<ConValue>>,
+    }
+
+    impl Environment {
+        /// Enter a nested scope
+        pub fn enter(self: &mut Box<Self>) {
+            let outer = std::mem::take(self);
+            self.outer = Some(outer);
+        }
+        /// Exits the scope, destroying all local variables and
+        /// returning the outer scope, if there is one
+        pub fn exit(&mut self) -> IResult<()> {
+            if let Some(outer) = std::mem::take(&mut self.outer) {
+                *self = *outer;
+                Ok(())
+            } else {
+                Err(Error::with_reason(Reason::ScopeExit))
+            }
+        }
+        /// Resolves a variable mutably
+        pub fn get_mut(&mut self, id: &Identifier) -> Option<&mut Option<ConValue>> {
+            match self.vars.get_mut(id) {
+                Some(var) => Some(var),
+                None => self.outer.as_mut().and_then(|o| o.get_mut(id)),
+            }
+        }
+        /// Resolves a variable immutably
+        pub fn get(&self, id: &Identifier) -> Option<&Option<ConValue>> {
+            match self.vars.get(id) {
+                Some(var) => Some(var),
+                None => self.outer.as_ref().and_then(|o| o.get(id)),
+            }
+        }
+        pub fn insert(&mut self, id: &Identifier, value: Option<ConValue>) {
+            self.vars.insert(id.clone(), value);
+        }
+    }
+}
+
 pub mod error {
     //! The [Error] type represents any error thrown by the [Interpreter](super::Interpreter)
+    use crate::ast::Identifier;
+
     use super::temp_type_impl::ConValue;
 
     pub type IResult<T> = Result<T, Error>;
@@ -524,11 +674,17 @@ pub mod error {
         Continue,
         /// Underflowed the stack
         StackUnderflow,
+        /// Exited the last scope
+        ScopeExit,
         /// Type incompatibility
         // TODO: store the type information in this error
         TypeError,
         /// In clause of For loop didn't yield a Range
         NotIterable,
+        /// A name was not defined in scope before being used
+        NotDefined(Identifier),
+        /// A name was defined but not initialized
+        NotInitialized(Identifier),
     }
 
     impl std::error::Error for Error {}
@@ -540,12 +696,19 @@ pub mod error {
     impl std::fmt::Display for Reason {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
             match self {
-                Reason::Return(value) => write!(f, "return {value:?}"),
+                Reason::Return(value) => write!(f, "return {value}"),
-                Reason::Break(value) => write!(f, "break {value:?}"),
+                Reason::Break(value) => write!(f, "break {value}"),
                 Reason::Continue => "continue".fmt(f),
                 Reason::StackUnderflow => "Stack underflow".fmt(f),
-                Reason::TypeError => "Type error".fmt(f),
+                Reason::ScopeExit => "Exited the last scope. This is a logic bug.".fmt(f),
+                Reason::TypeError => "Incompatible types".fmt(f),
                 Reason::NotIterable => "`in` clause of `for` loop did not yield an iterable".fmt(f),
+                Reason::NotDefined(value) => {
+                    write!(f, "{} not bound. Did you mean `let {};`?", value.0, value.0)
+                }
+                Reason::NotInitialized(value) => {
+                    write!(f, "{} bound, but not initialized", value.0)
+                }
             }
         }
     }

libconlang/src/parser.rs

@@ -8,7 +8,7 @@ pub mod error {
     use std::fmt::Display;
 
     /// The reason for the [Error]
-    #[derive(Clone, Debug, Default, PartialEq, Eq)]
+    #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
     pub enum Reason {
         Expected(Type),
         Unexpected(Type),
@@ -101,7 +101,11 @@ pub mod error {
             self.start.as_ref()
         }
         /// Gets the [Reason] for this error
-        pub fn reason(self, reason: Reason) -> Self {
+        pub fn reason(&self) -> Reason {
+            self.reason
+        }
+        /// Modifies the [Reason] of this error
+        pub fn with_reason(self, reason: Reason) -> Self {
             Self { reason, ..self }
         }
         error_impl! {
@@ -131,6 +135,7 @@ pub mod error {
 pub struct Parser {
     tokens: Vec<Token>,
     panic_stack: Vec<usize>,
+    pub errors: Vec<Error>,
     cursor: usize,
 }
 impl<'t> From<Lexer<'t>> for Parser {
@@ -153,7 +158,7 @@ impl Parser {
     ///
     /// [1]: Token
     pub fn new(tokens: Vec<Token>) -> Self {
-        Self { tokens, panic_stack: vec![], cursor: 0 }
+        Self { tokens, panic_stack: vec![], errors: vec![], cursor: 0 }
     }
     /// Parses the [start of an AST](Start)
     pub fn parse(&mut self) -> PResult<Start> {
@@ -184,6 +189,10 @@ impl Parser {
         self.consume_comments();
         self
     }
+}
+/// Panicking
+#[allow(dead_code)]
+impl Parser {
     /// Records the current position on the panic stack
     fn mark(&mut self) -> &mut Self {
         self.panic_stack.push(self.cursor);
@@ -204,11 +213,22 @@ impl Parser {
     fn advance_until(&mut self, t: Type) -> PResult<&mut Self> {
         while self.matches(t).is_err() {
             self.check_eof()
-                .map_err(|e| e.reason(Expected(t)))?
+                .map_err(|e| e.with_reason(Expected(t)))?
                 .consume();
         }
         Ok(self)
     }
+    /// Marks the current position, and unwinds the panic stack if `f` fails.
+    fn attempt<F, R>(&mut self, f: F) -> PResult<R>
+    where F: FnOnce(&mut Self) -> PResult<R> {
+        self.mark();
+        let out = f(self);
+        match out {
+            Ok(_) => self.unmark(),
+            Err(_) => self.unwind()?,
+        };
+        out
+    }
 }
 /// Helpers
 impl Parser {
@@ -241,22 +261,6 @@ impl Parser {
         self.matches(t)?;
         Ok(self.consume())
     }
-    /// Parses anything wrapped in `lhs` and `rhs` delimiters.
-    fn delimited<F, R>(&mut self, lhs: Type, mid: F, rhs: Type) -> PResult<R>
-    where F: Fn(&mut Self) -> PResult<R> {
-        self.consume_type(lhs)?.mark();
-        let out = match mid(self) {
-            Ok(out) => out,
-            Err(e) => {
-                eprintln!("{e}");
-                // Jump back in time and try to re-parse from the next brace
-                self.unwind()?.advance_until(lhs)?.mark();
-                return self.delimited(lhs, mid, rhs);
-            }
-        };
-        self.consume_type(rhs)?.unmark();
-        Ok(out)
-    }
     #[doc(hidden)]
     fn todo_error(&mut self, l: u32, c: u32, s: &str) -> Error {
         eprintln!("TODO: {s}:{l}:{c}");
@@ -359,15 +363,7 @@ impl Parser {
     fn stmt(&mut self) -> PResult<Stmt> {
         let token = self.peek()?;
         match token.ty() {
-            Type::Keyword(Keyword::Let) => Ok(Stmt::Let {
+            Type::Keyword(Keyword::Let) => self.let_stmt().map(Stmt::Let),
-                mutable: self.consume().keyword(Keyword::Mut).is_ok(),
-                name: self.identifier()?,
-                ty: self
-                    .consume_type(Type::Colon)
-                    .and_then(Self::identifier)
-                    .ok(),
-                init: self.consume_type(Type::Eq).and_then(Self::expr).ok(),
-            }),
             _ => {
                 let out = Stmt::Expr(self.expr()?);
                 self.consume_type(Type::Semi)?;
@@ -375,6 +371,23 @@ impl Parser {
             }
         }
     }
+    /// Parses a [Let] statement
+    fn let_stmt(&mut self) -> PResult<Let> {
+        let out = Let {
+            mutable: self.consume().keyword(Keyword::Mut).is_ok(),
+            name: self.identifier()?,
+            ty: self
+                .consume_type(Type::Colon)
+                .and_then(Self::identifier)
+                .ok(),
+            init: self.consume_type(Type::Eq).and_then(Self::expr).ok(),
+        };
+        self.consume_type(Type::Semi)?;
+        Ok(out)
+    }
+    // /// Parses a [Function] statement
+    // fn function_stmt(&mut self) -> PResult<Function> {
+    // }
 }
 /// Expressions
 impl Parser {
@@ -385,8 +398,23 @@ impl Parser {
     }
     /// Parses a [block expression](expression::Block)
     fn block(&mut self) -> PResult<expression::Block> {
-        self.delimited(Type::LCurly, |p| p.expr(), Type::RCurly)
+        use expression::{Block, Expr};
-            .map(|e| expression::Block { expr: Box::new(e) })
+        let mut statements = vec![];
+        let mut expr: Option<Box<Expr>> = None;
+        self.consume_type(Type::LCurly)?;
+        // tHeRe Is No PlAcE iN yOuR gRaMmAr WhErE bOtH aN eXpReSsIoN aNd A sTaTeMeNt ArE eXpEcTeD
+        while self.consume_type(Type::RCurly).is_err() {
+            match self.expr() {
+                Ok(e) if self.consume_type(Type::Semi).is_ok() => statements.push(Stmt::Expr(e)),
+                Ok(e) => {
+                    expr = Some(Box::new(e));
+                    self.consume_type(Type::RCurly)?;
+                    break;
+                }
+                Err(_) => statements.push(self.stmt()?),
+            }
+        }
+        Ok(Block { statements, expr })
     }
     /// Parses a [group expression](expression::Group)
     fn group(&mut self) -> PResult<expression::Group> {
@@ -440,20 +468,35 @@ impl Parser {
 macro binary ($($f:ident = $a:ident, $b:ident);*$(;)?) {$(
     #[doc = concat!("Parses a(n) [", stringify!($f), " operation](math::Operation::Binary) expression")]
     fn $f (&mut self) -> PResult<math::Operation> {
-        let (first, mut others) = (self.$a()?, vec![]);
+        use math::{Operation, Binary};
+        let (first, mut other) = (self.$a()?, vec![]);
         while let Ok(op) = self.$b() {
-            others.push((op, self.$a()?));
+            other.push((op, self.$a()?));
         }
-        Ok(if others.is_empty() { first } else {
+        Ok(if other.is_empty() { first } else {
-            math::Operation::binary(first, others)
+            Operation::Binary(Binary { first: first.into(), other })
         })
     }
 )*}
 /// # [Arithmetic and Logical Subexpressions](math)
 impl Parser {
+    fn assign(&mut self) -> PResult<math::Operation> {
+        use math::{Assign, Operation};
+        let next = self.compare()?;
+        let Ok(operator) = self.assign_op() else {
+            return Ok(next);
+        };
+        let Operation::Primary(expression::Primary::Identifier(target)) = next else {
+            return Ok(next);
+        };
+        Ok(Operation::Assign(Assign {
+            target,
+            operator,
+            init: self.assign()?.into(),
+        }))
+    }
     binary! {
         // name   operands operators
-        assign  = compare, assign_op;
         compare = range,   compare_op;
         range   = logic,   range_op;
         logic   = bitwise, logic_op;
@@ -464,11 +507,22 @@ impl Parser {
     }
     /// Parses a [unary operation](math::Operation::Unary) expression
     fn unary(&mut self) -> PResult<math::Operation> {
+        use math::{Operation, Unary};
         let mut operators = vec![];
         while let Ok(op) = self.unary_op() {
             operators.push(op)
         }
-        Ok(math::Operation::Unary { operators, operand: self.primary()? })
+        if operators.is_empty() {
+            return self.primary_operation();
+        }
+        Ok(Operation::Unary(Unary {
+            operators,
+            operand: self.primary_operation()?.into(),
+        }))
+    }
+    /// Parses a [primary operation](math::Operation::Primary) expression
+    fn primary_operation(&mut self) -> PResult<math::Operation> {
+        Ok(math::Operation::Primary(self.primary()?))
     }
 }
 macro operator_impl ($($(#[$m:meta])* $f:ident : {$($type:pat => $op:ident),*$(,)?})*) {
@@ -528,20 +582,27 @@ impl Parser {
             Type::GtEq => GreaterEq,
             Type::Gt => Greater,
         }
-        /// Parses an [assign operator](operator)
+    }
-        assign_op: {
+    /// Parses an [assign operator](operator::Assign)
-            Type::Eq => Assign,
+    fn assign_op(&mut self) -> PResult<operator::Assign> {
-            Type::PlusEq => AddAssign,
+        use operator::Assign;
-            Type::MinusEq => SubAssign,
+        let token = self.peek()?;
-            Type::StarEq => MulAssign,
+        let out = Ok(match token.ty() {
-            Type::SlashEq => DivAssign,
+            Type::Eq => Assign::Assign,
-            Type::RemEq => RemAssign,
+            Type::PlusEq => Assign::AddAssign,
-            Type::AmpEq => BitAndAssign,
+            Type::MinusEq => Assign::SubAssign,
-            Type::BarEq => BitOrAssign,
+            Type::StarEq => Assign::MulAssign,
-            Type::XorEq => BitXorAssign,
+            Type::SlashEq => Assign::DivAssign,
-            Type::LtLtEq => ShlAssign,
+            Type::RemEq => Assign::RemAssign,
-            Type::GtGtEq => ShrAssign,
+            Type::AmpEq => Assign::BitAndAssign,
-        }
+            Type::BarEq => Assign::BitOrAssign,
+            Type::XorEq => Assign::BitXorAssign,
+            Type::LtLtEq => Assign::ShlAssign,
+            Type::GtGtEq => Assign::ShrAssign,
+            _ => Err(Error::not_operator().token(token.clone()))?,
+        });
+        self.consume();
+        out
     }
     /// Parses a [unary operator](operator::Unary)
     fn unary_op(&mut self) -> PResult<operator::Unary> {
@@ -578,7 +639,7 @@ impl Parser {
             Type::Keyword(Continue) => self.parse_continue().map(Flow::Continue),
             e => Err(Error::unexpected(e).token(token.clone()))?,
         }
-        .map_err(|e| e.reason(IncompleteBranch))
+        .map_err(|e| e.with_reason(IncompleteBranch))
     }
     /// Parses an [if](control::If) expression
     fn parse_if(&mut self) -> PResult<control::If> {

libconlang/src/pretty_printer.rs

@@ -13,10 +13,10 @@ pub trait PrettyPrintable {
 }
 impl PrettyPrintable for Start {
     fn print(&self) {
-        let _ = self.walk(&mut Printer::default());
+        let _ = Printer::default().visit(self);
     }
     fn write(&self, into: impl Write) -> IOResult<()> {
-        self.walk(&mut Printer::from(into))
+        Printer::from(into).visit(self)
     }
 }
 
@@ -70,47 +70,75 @@ macro visit_operator($self:ident.$op:expr) {
 impl<W: Write> Visitor<IOResult<()>> for Printer<W> {
     fn visit_program(&mut self, prog: &Program) -> IOResult<()> {
         // delegate to the walker
-        prog.walk(self)
+        for stmt in &prog.0 {
+            self.visit_statement(stmt)?;
+        }
+        Ok(())
     }
     fn visit_statement(&mut self, stmt: &Stmt) -> IOResult<()> {
         match stmt {
-            Stmt::Let { name, mutable, ty, init } => {
+            Stmt::Let(stmt) => self.visit_let(stmt)?,
-                self.put("let")?.space()?;
-                if *mutable {
-                    self.put("mut")?.space()?;
-                }
-                self.visit_identifier(name)?;
-                if let Some(ty) = ty {
-                    self.put(':')?.space()?.visit_identifier(ty)?;
-                }
-                if let Some(init) = init {
-                    self.space()?.put('=')?.space()?.visit_expr(init)?;
-                }
-            },
             Stmt::Expr(e) => {
                 self.visit_expr(e)?;
-            },
+                self.put(';').map(drop)?
+            }
         }
-        self.put(';')?.newline().map(drop)
+        self.newline().map(drop)
     }
-    fn visit_operation(&mut self, expr: &math::Operation) -> IOResult<()> {
+    fn visit_let(&mut self, stmt: &Let) -> IOResult<()> {
-        use math::Operation;
+        let Let { name, mutable, ty, init } = stmt;
-        match expr {
+        self.put("let")?.space()?;
-            Operation::Binary { first, other } => {
+        if *mutable {
-                self.put('(')?.visit_operation(first)?;
+            self.put("mut")?.space()?;
-                for (op, other) in other {
-                    self.visit_binary_op(op)?;
-                    self.visit_operation(other)?;
-                }
-                self.put(')').map(drop)
-            }
-            Operation::Unary { operators, operand } => {
-                for op in operators {
-                    self.visit_unary_op(op)?;
-                }
-                self.visit_primary(operand)
-            }
         }
+        self.visit_identifier(name)?;
+        if let Some(ty) = ty {
+            self.put(':')?.space()?.visit_identifier(ty)?;
+        }
+        if let Some(init) = init {
+            self.space()?.put('=')?.space()?.visit_expr(init)?;
+        }
+        self.put(';').map(drop)
+    }
+
+    fn visit_assign(&mut self, assign: &math::Assign) -> IOResult<()> {
+        let math::Assign { target, operator, init } = assign;
+        self.visit_identifier(target)?;
+        self.visit_assign_op(operator)?;
+        self.visit_operation(init)
+    }
+    fn visit_binary(&mut self, binary: &math::Binary) -> IOResult<()> {
+        let math::Binary { first, other } = binary;
+        self.put('(')?.visit_operation(first)?;
+        for (op, other) in other {
+            self.visit_binary_op(op)?;
+            self.visit_operation(other)?;
+        }
+        self.put(')').map(drop)
+    }
+    fn visit_unary(&mut self, unary: &math::Unary) -> IOResult<()> {
+        let math::Unary { operators, operand } = unary;
+        for op in operators {
+            self.visit_unary_op(op)?;
+        }
+        self.visit_operation(operand)
+    }
+
+    fn visit_assign_op(&mut self, op: &operator::Assign) -> IOResult<()> {
+        use operator::Assign;
+        visit_operator!(self.match op {
+            Assign::Assign => "=",
+            Assign::AddAssign => "+=",
+            Assign::SubAssign => "-=",
+            Assign::MulAssign => "*=",
+            Assign::DivAssign => "/=",
+            Assign::RemAssign => "%=",
+            Assign::BitAndAssign => "&=",
+            Assign::BitOrAssign => "|=",
+            Assign::BitXorAssign => "^=",
+            Assign::ShlAssign => "<<=",
+            Assign::ShrAssign => ">>=",
+        })
     }
     fn visit_binary_op(&mut self, op: &operator::Binary) -> IOResult<()> {
         use operator::Binary;
@@ -136,17 +164,6 @@ impl<W: Write> Visitor<IOResult<()>> for Printer<W> {
             Binary::NotEq => "!=",
             Binary::GreaterEq => ">=",
             Binary::Greater => ">",
-            Binary::Assign => "=",
-            Binary::AddAssign => "+=",
-            Binary::SubAssign => "-=",
-            Binary::MulAssign => "*=",
-            Binary::DivAssign => "/=",
-            Binary::RemAssign => "%=",
-            Binary::BitAndAssign => "&=",
-            Binary::BitOrAssign => "|=",
-            Binary::BitXorAssign => "^=",
-            Binary::ShlAssign => "<<=",
-            Binary::ShrAssign => ">>=",
         })
     }
     fn visit_unary_op(&mut self, op: &operator::Unary) -> IOResult<()> {
@@ -223,18 +240,28 @@ impl<W: Write> Visitor<IOResult<()>> for Printer<W> {
         self.put(int).map(drop)
     }
     fn visit_empty(&mut self) -> IOResult<()> {
-        self.put("").map(drop)
+        self.put("()").map(drop)
     }
 
-    fn visit_block(&mut self, expr: &expression::Block) -> IOResult<()> {
+    fn visit_block(&mut self, block: &expression::Block) -> IOResult<()> {
         self.put('{')?.indent().newline()?;
-        expr.walk(self)?;
+        for stmt in &block.statements {
+            self.visit_statement(stmt)?;
+        }
+        for expr in &block.expr {
+            self.visit_expr(expr)?;
+        }
         self.dedent().newline()?.put('}').map(drop)
     }
 
     fn visit_group(&mut self, expr: &expression::Group) -> IOResult<()> {
-        self.put('(')?.space()?;
+        match expr {
-        expr.walk(self)?;
+            expression::Group::Expr(expr) => {
-        self.space()?.put(')').map(drop)
+                self.put('(')?.space()?;
+                self.visit_expr(expr)?;
+                self.space()?.put(')').map(drop)
+            }
+            expression::Group::Empty => self.visit_empty(),
+        }
     }
 }