major cleanups: switch to dynamic Errors, impl Context, rename enums/records to unions/structs

11 files changed, 342 insertions, 309 deletions

diff --git a/README.md b/README.md
index 7140111..3f28020 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,10 @@
-# chrysanthemum: a simple type system
+# chrysanthemum
+
+chrysanthemum is a simple language with a type system, initially written as a term project for CPSC 539.
+It implements a number of features from the excellent *Types and Programming Languages*, including:
+- The simply typed lambda calculus
+- Bidirectional type checking and subtyping support
+- A somewhat complex type system: including support for `unit`, `bool`, `nat`, `int`, `float`, `str`, `union`, `struct`, `empty`, and `err` types
 
 ## todo
 
@@ -8,19 +14,30 @@
 - [x] bidirectional typechecking: implement `infer` and `check`
 - [x] extend to additional basic types: refactor `Term`
 - [ ] extend to complex types: implement `access`
-- [ ] simple effects: extend `ast`
 - [ ] type classes: implement `monomorphize`
+- [ ] simple effects: extend `ast`
 - [x] testtesttest
 
 ## architecture
 
 ```bash
 src/
-src/main.rs # the user facing program
-src/parser.rs # parses user programs into proper data structures
-src/ast.rs # the fundamental representation of the program
-src/simple.rs # the core of the lambda calculus: checking, inference, evaluation
-src/effects.rs # code for effects idk
-src/classes.rs # a monomorphization pass for type classes
+src/main.rs    # the user facing program
+src/simple.rs  # the simple lambda calculus: execution
+src/ast.rs     # the fundamental representation of types and terms
+src/bidirectional.rs # the core of the language: checking, inference
+src/unification.rs   # an alternate core: checking and inference by unification
+src/parser.rs        # parses user programs into proper data structures
+src/monomorphize.rs  # a monomorphization pass for type classes
+src/effects.rs       # code for effects idk
 test/ # various tests
 ```
+
+## bibliography
+
+- [TAPL](https://www.cis.upenn.edu/~bcpierce/tapl/)
+- [Bidirectional Typing Rules: A Tutorial](https://www.davidchristiansen.dk/tutorials/bidirectional.pdf)
+- [Bidirectional Typechecking](https://research.cs.queensu.ca/home/jana/bitype.pdf)
+- [Typechecking for Higher-Rank Polymorphism](https://arxiv.org/pdf/1306.6032.pdf)
+- [Bidirectional Type Class Instances](https://arxiv.org/pdf/1906.12242.pdf)
+- [How to make ad-hoc polymorphism less ad-hoc](https://dl.acm.org/doi/pdf/10.1145/75277.75283)
diff --git a/src/ast.rs b/src/ast.rs
index bd0d8b4..6bb7171 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -1,10 +1,10 @@
-// The abstract syntax tree. All supported types go here.
-
-use core::fmt;
 use std::collections::HashMap;
 
+pub type Result<T> = core::result::Result<T, Box<dyn std::error::Error>>;
 pub type Identifier = String;
-pub type Context = HashMap<Identifier, Term>;
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Context(HashMap<Identifier, Term>);
 
 // note: built-in functions do NOT go here!
 #[derive(Debug, Clone, PartialEq)]
@@ -18,6 +18,7 @@ pub enum Expression {
     Conditional{if_cond: Box<Expression>, if_then: Box<Expression>, if_else: Box<Expression>}
 }
 
+/// All supported types.
 #[derive(Debug, Clone, PartialEq)]
 pub enum Type {
     Empty,
@@ -28,11 +29,12 @@ pub enum Type {
     Integer,
     Float,
     String,
-    Enum(Vec<Type>),
-    Record(HashMap<Identifier, Type>),
+    Union(Vec<Type>),
+    Struct(HashMap<Identifier, Type>),
     Function{from: Box<Type>, to: Box<Type>},
 }
 
+/// Data associated with a type.
 #[derive(Debug, Clone, PartialEq)]
 pub enum Term {
     Unit(),
@@ -41,13 +43,71 @@ pub enum Term {
     Integer(isize),
     Float(f32),
     String{len: usize, cap: usize, data: Vec<usize>},
-    Enum{val: usize, data: Box<Term>}, // is this right?
-    Record(HashMap<Identifier, Term>), // is this right?
+    Union{val: usize, data: Box<Term>}, // is this right?
+    Struct(HashMap<Identifier, Term>), // is this right?
     Function(Box<Expression>) // this should allow us to bind functions
 }
 
-impl fmt::Display for Expression {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl Term {
+    /// Convert a term into its corresponding type.
+    pub fn convert(&self) -> Result<Type> {
+        match self {
+            Term::Unit() => Ok(Type::Unit),
+            Term::Boolean(_) => Ok(Type::Boolean),
+            Term::Natural(_) => Ok(Type::Natural),
+            Term::Integer(_) => Ok(Type::Integer),
+            Term::Float(_) => Ok(Type::Float),
+            Term::String { len, cap, data } => Ok(Type::String),
+            Term::Union { val, data } => data.convert(),
+            Term::Struct(data) => {
+                let mut result = HashMap::new();
+                for (key, val) in data {
+                    result.insert(key.clone(), val.convert()?);
+                }
+                return Ok(Type::Struct(result));
+            },
+            Term::Function(func) => match *func.clone() {
+                Expression::Annotation { expr, kind } => match kind {
+                    Type::Function { from, to } => Ok(Type::Function { from, to }),
+                    _ => Err("function term value not a function!".into())
+                }
+                _ => Err("function term value does not have an annotation!".into())
+            }
+        }
+    }
+}
+
+impl Type {
+    /// Get the default value of a type. Throws an error if it doesn't exist.
+    pub fn default(&self) -> Result<Term> {
+        match self {
+            Type::Empty => Err("attempting to take the default term for empty".into()),
+            Type::Error => Err("attempting to take the default term for error".into()),
+            Type::Unit => Ok(Term::Unit()),
+            Type::Boolean => Ok(Term::Boolean(false)),
+            Type::Natural => Ok(Term::Natural(0)),
+            Type::Integer => Ok(Term::Integer(0)),
+            Type::Float => Ok(Term::Float(0.0)),
+            Type::String => Ok(Term::String { len: 0, cap: 0, data: vec!()}),
+            Type::Union(data) => match data.len() {
+                0 => Err("attempting to get a default term of an enum with no variants!".into()),
+                _ => Ok(Term::Union { val: 0, data: Box::new(data.get(0).unwrap().default()?) })
+            },
+            Type::Struct(data) => {
+                let mut result = HashMap::new();
+                for (key, val) in data {
+                    result.insert(key.clone(), val.default()?);
+                }
+                return Ok(Term::Struct(result));
+            },
+            Type::Function { from, to } =>
+                Err("attempting to take the default term of a function type".into()),
+        }
+    }
+}
+
+impl core::fmt::Display for Expression {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
             Expression::Annotation { expr, kind } => write!(f, "({}: {})", expr, kind),
             Expression::Constant { term } => write!(f, "'{:?}", term),
@@ -59,8 +119,8 @@ impl fmt::Display for Expression {
     }
 }
 
-impl fmt::Display for Type {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl core::fmt::Display for Type {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
             Type::Empty => write!(f, "⊤"),
             Type::Error => write!(f, "⊥"),
@@ -70,15 +130,15 @@ impl fmt::Display for Type {
             Type::Integer => write!(f, "int"),
             Type::Float => write!(f, "float"),
             Type::String => write!(f, "str"),
-            Type::Enum(data) => write!(f, "({:?})", data),
-            Type::Record(data) => write!(f, "{{{:?}}}", data),
+            Type::Union(data) => write!(f, "({:?})", data),
+            Type::Struct(data) => write!(f, "{{{:?}}}", data),
             Type::Function { from, to } => write!(f, "{}->{}", from, to),
         }
     }
 }
 
-impl fmt::Display for Term {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl core::fmt::Display for Term {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
             Term::Unit() => write!(f, "∅"),
             Term::Boolean(term) => write!(f, "{}", term),
@@ -86,90 +146,21 @@ impl fmt::Display for Term {
             Term::Integer(term) => write!(f, "{}", term),
             Term::Float(term) => write!(f, "{}", term),
             Term::String { len, cap, data } => write!(f, "\"{:?}\"", data),
-            Term::Enum { val, data } => write!(f, "{:?}", data),
-            Term::Record(term) => write!(f, "{:?}", term),
+            Term::Union { val, data } => write!(f, "{:?}", data),
+            Term::Struct(term) => write!(f, "{:?}", term),
             Term::Function(expr) => write!(f, "{}", *expr),
         }
     }
 }
 
-// hatehatehate that you can't implement a trait for foreign types
-// impl<T> fmt::Display for Vec<T> where T: fmt::Display {
-//     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-//         for (i, val) in self.enumerate() {
-//             if i == 0 {
-//                 write!(f, "{}", val);
-//             } else {
-//                 write!(f, ",{}", val);
-//             }
-//         }
-//         return Ok(());
-//     }
-// }
-
-// impl<T, U> fmt::Display for HashMap<T, U> where T: fmt::Display, U: fmt::Display {
-//     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-//         for (i, (key, val)) in self.enumerate() {
-//             if i == 0 {
-//                 write!(f, "{}={}", key, val);
-//             } else {
-//                 write!(f, ",{}={}", key, val);
-//             }
-//         }
-//         return Ok(());
-//     }
-// }
-
-/// Convert a term into its corresponding type.
-pub fn convert(term: &Term) -> Result<Type, String> {
-    match term {
-        Term::Unit() => Ok(Type::Unit),
-        Term::Boolean(_) => Ok(Type::Boolean),
-        Term::Natural(_) => Ok(Type::Natural),
-        Term::Integer(_) => Ok(Type::Integer),
-        Term::Float(_) => Ok(Type::Float),
-        Term::String { len, cap, data } => Ok(Type::String),
-        Term::Enum { val, data } => convert(data),
-        Term::Record(data) => {
-            let mut result = HashMap::new();
-            for (key, val) in data {
-                result.insert(key.clone(), convert(val)?);
-            }
-            return Ok(Type::Record(result));
-        },
-        Term::Function(func) => match *func.clone() {
-            Expression::Annotation { expr, kind } => match kind {
-                Type::Function { from, to } => Ok(Type::Function { from, to }),
-                _ => Err("function term value not a function!".to_string())
-            }
-            _ => Err("function term value does not have an annotation!".to_string())
-        }
+impl Context {
+    pub fn new() -> Self {
+        Context(HashMap::new())
     }
-}
-
-/// Get the default value of a type. Throws an error if it doesn't exist.
-pub fn default(kind: &Type) -> Result<Term, String> {
-    match kind {
-        Type::Empty => Err("attempting to take the default term for empty".to_string()),
-        Type::Error => Err("attempting to take the default term for error".to_string()),
-        Type::Unit => Ok(Term::Unit()),
-        Type::Boolean => Ok(Term::Boolean(false)),
-        Type::Natural => Ok(Term::Natural(0)),
-        Type::Integer => Ok(Term::Integer(0)),
-        Type::Float => Ok(Term::Float(0.0)),
-        Type::String => Ok(Term::String { len: 0, cap: 0, data: vec!()}),
-        Type::Enum(data) => match data.len() {
-            0 => Err("attempting to get a default term of an enum with no variants!".to_string()),
-            _ => Ok(Term::Enum { val: 0, data: Box::new(default(data.get(0).unwrap())?) })
-        },
-        Type::Record(data) => {
-            let mut result = HashMap::new();
-            for (key, val) in data {
-                result.insert(key.clone(), default(val)?);
-            }
-            return Ok(Term::Record(result));
-        },
-        Type::Function { from, to } =>
-            Err("attempting to take the default term of a function type".to_string()),
+    pub fn get(&self, k: &Identifier) -> Option<&Term> {
+        self.0.get(k)
+    }
+    pub fn insert(&mut self, k: Identifier, v: Term) -> Option<Term> {
+        self.0.insert(k, v)
     }
 }
diff --git a/src/bidirectional.rs b/src/bidirectional.rs
index 493ae2f..d62267c 100644
--- a/src/bidirectional.rs
+++ b/src/bidirectional.rs
@@ -2,119 +2,122 @@
 
 use crate::ast::*;
 
-/// Checking judgement: takes an expression and a type to check against and calls out to `infer` as needed.
-pub fn check(context: &Context, expression: Expression, target: &Type) -> Result<(), String> {
-    match expression {
-        // fall through to inference mode
-        Expression::Annotation { expr, kind } => {
-            let result = infer(context, Expression::Annotation { expr, kind })?;
-            return match subtype(&result, &target) {
-                true => Ok(()),
-                false => Err(format!("inferred type {result} does not match target {target}"))
-            }
-        },
-        // Bt-CheckInfer
-        Expression::Constant { term } => match subtype(&convert(&term)?, &target) {
-            true => Ok(()),
-            false => Err(format!("constant is of wrong type, expected {target}"))
-            // false => Ok(()) // all our constants are Empty for now
-        },
-        // Bt-CheckInfer
-        Expression::Variable { id } => match context.get(&id) {
-            Some(term) if subtype(&convert(term)?, &target) => Ok(()),
-            Some(_) => Err(format!("variable {id} is of wrong type")),
-            None => Err(format!("failed to find variable {id} in context"))
-        },
-        // Bt-Abs
-        Expression::Abstraction { param, func } => match target {
-            Type::Function { from, to } => {
-                let mut context = context.clone();
-                context.insert(param, default(from)?);
-                return check(&context, *func, &to);
+impl Context {
+    /// Checking judgement: takes an expression and a type to check against and calls out to `infer` as needed.
+    pub fn check(&self, expression: Expression, target: &Type) -> Result<()> {
+        match expression {
+            // fall through to inference mode
+            Expression::Annotation { expr, kind } => {
+                let result = self.infer(Expression::Annotation { expr, kind })?;
+                return match result.subtype(&target) {
+                    true => Ok(()),
+                    false => Err(format!("inferred type {result} does not match target {target}").into())
+                }
             },
-            _ => Err(format!("attempting to check an abstraction with a non-function type {target}"))
-        },
-        // fall through to inference mode
-        Expression::Application { func, arg } => {
-            let result = &infer(context, Expression::Application { func, arg })?;
-            return match subtype(&result, &target) {
+            // Bt-CheckInfer
+            Expression::Constant { term } => match &term.convert()?.subtype(&target) {
                 true => Ok(()),
-                false => Err(format!("inferred type {result} does not match {target}"))
+                false => Err(format!("constant is of wrong type, expected {target}").into())
+                // false => Ok(()) // all our constants are Empty for now
+            },
+            // Bt-CheckInfer
+            Expression::Variable { id } => match self.get(&id) {
+                Some(term) if term.convert()?.subtype(&target) => Ok(()),
+                Some(_) => Err(format!("variable {id} is of wrong type").into()),
+                None => Err(format!("failed to find variable {id} in context").into())
+            },
+            // Bt-Abs
+            Expression::Abstraction { param, func } => match target {
+                Type::Function { from, to } => {
+                    let mut context = self.clone();
+                    context.insert(param, from.default()?);
+                    return context.check(*func, &to);
+                },
+                _ => Err(format!("attempting to check an abstraction with a non-function type {target}").into())
+            },
+            // fall through to inference mode
+            Expression::Application { func, arg } => {
+                let result = &self.infer(Expression::Application { func, arg })?;
+                return match result.subtype(&target) {
+                    true => Ok(()),
+                    false => Err(format!("inferred type {result} does not match {target}").into())
+                }
+            },
+            // T-If
+            Expression::Conditional { if_cond, if_then, if_else } => {
+                self.check(*if_cond, &Type::Boolean)?;
+                self.check(*if_then, &target)?;
+                self.check(*if_else, &target)?;
+                return Ok(());
             }
-        },
-        // T-If
-        Expression::Conditional { if_cond, if_then, if_else } => {
-            check(context, *if_cond, &Type::Boolean)?;
-            check(context, *if_then, &target)?;
-            check(context, *if_else, &target)?;
-            return Ok(());
         }
     }
-}
 
-/// Inference judgement: takes an expression and attempts to infer the associated type.
-pub fn infer(context: &Context, expression: Expression) -> Result<Type, String> {
-    match expression {
-        // Bt-Ann
-        Expression::Annotation { expr, kind } => check(context, *expr, &kind).map(|x| kind),
-        // Bt-True / Bt-False / etc
-        Expression::Constant { term } => convert(&term),
-        // Bt-Var
-        Expression::Variable { id } => match context.get(&id) {
-            Some(term) => infer(&Context::new(), Expression::Constant { term: term.clone() }),
-            None => Err(format!("failed to find variable in context {context:?}"))
-        },
-        // Bt-App
-        Expression::Application { func, arg } => match infer(context, *func)? {
-            Type::Function { from, to } => check(context, *arg, &*from).map(|x| *to),
-            _ => Err(format!("application abstraction is not a function type"))
-        },
-        // inference from an abstraction is always an error
-        // we could try and infer the func without adding the parameter to scope:
-        // but this is overwhelmingly likely to be an error, so just report it now.
-        Expression::Abstraction { param, func } =>
-            Err(format!("attempting to infer from an abstraction")),
-        // idk
-        Expression::Conditional { if_cond, if_then, if_else } => {
-            check(context, *if_cond, &Type::Boolean)?;
-            let if_then = infer(context, *if_then)?;
-            let if_else = infer(context, *if_else)?;
-            if subtype(&if_then, &if_else) && subtype(&if_else, &if_then) {
-                Ok(if_then) // fixme: should be the join
-            } else {
-                Err(format!("if clauses of different types: {if_then} and {if_else}"))
+    /// Inference judgement: takes an expression and attempts to infer the associated type.
+    pub fn infer(&self, expression: Expression) -> Result<Type> {
+        match expression {
+            // Bt-Ann
+            Expression::Annotation { expr, kind } => self.check(*expr, &kind).map(|x| kind),
+            // Bt-True / Bt-False / etc
+            Expression::Constant { term } => term.convert(),
+            // Bt-Var
+            Expression::Variable { id } => match self.get(&id) {
+                Some(term) => Context::new().infer(Expression::Constant { term: term.clone() }),
+                None => Err(format!("failed to find variable in context {self:?}").into())
+            },
+            // Bt-App
+            Expression::Application { func, arg } => match self.infer(*func)? {
+                Type::Function { from, to } => self.check(*arg, &*from).map(|x| *to),
+                _ => Err(format!("application abstraction is not a function type").into())
+            },
+            // inference from an abstraction is always an error
+            // we could try and infer the func without adding the parameter to scope:
+            // but this is overwhelmingly likely to be an error, so just report it now.
+            Expression::Abstraction { param, func } =>
+                Err(format!("attempting to infer from an abstraction").into()),
+            // idk
+            Expression::Conditional { if_cond, if_then, if_else } => {
+                self.check(*if_cond, &Type::Boolean)?;
+                let if_then = self.infer(*if_then)?;
+                let if_else = self.infer(*if_else)?;
+                if if_then.subtype(&if_else) && if_else.subtype(&if_then) {
+                    Ok(if_then) // fixme: should be the join
+                } else {
+                    Err(format!("if clauses of different types: {if_then} and {if_else}").into())
+                }
             }
         }
     }
 }
 
-/// The subtyping relation between any two types.
-pub fn subtype(is: &Type, of: &Type) -> bool {
-    match (is, of) {
-        (Type::Record(is_fields), Type::Record(of_fields)) => {
-            // width, depth, and permutation
-            for (key, of_value) in of_fields {
-                match is_fields.get(key) {
-                    Some(is_value) => {
-                        if !subtype(is_value, of_value) {
-                            return false;
+impl Type {
+    /// The subtyping relation between any two types.
+    pub fn subtype(&self, other: &Self) -> bool {
+        match (self, other) {
+            (Type::Struct(is_fields), Type::Struct(of_fields)) => {
+                // width, depth, and permutation
+                for (key, of_value) in of_fields {
+                    match is_fields.get(key) {
+                        Some(is_value) => {
+                            if !is_value.subtype(of_value) {
+                                return false;
+                            }
                         }
+                        None => return false
                     }
-                    None => return false
                 }
-            }
-            return true;
-        },
-        (Type::Enum(is_variants), Type::Enum(of_variants)) => false, // fixme
-        (Type::Function { from: is_from, to: is_to },
-         Type::Function { from: of_from, to: of_to }) => {
-            subtype(of_from, is_from) && subtype(is_to, of_to)
-        },
-        (Type::Natural, Type::Integer) => true, // obviously not, but let's pretend
-        (_, Type::Empty) => true,
-        (Type::Error, _) => true,
-        (_, _) if is == of => true,
-        (_, _) => false
+                return true;
+            },
+            (Type::Union(is_variants), Type::Union(of_variants)) => false, // fixme
+            (Type::Function { from: is_from, to: is_to },
+             Type::Function { from: of_from, to: of_to }) => {
+                of_from.subtype(is_from) && is_to.subtype(of_to)
+            },
+            (Type::Natural, Type::Integer) => true, // obviously not, but let's pretend
+            (_, Type::Empty) => true,
+            (Type::Error, _) => true,
+            (_, _) if self == other => true,
+            (_, _) => false
+        }
     }
 }
-
diff --git a/src/classes.rs b/src/classes.rs
deleted file mode 100644
index 38a4847..0000000
--- a/src/classes.rs
+++ /dev/null
@@ -1,3 +0,0 @@
-// Typeclass pass: monomorphize based on usage, pretty much
-
-
diff --git a/src/main.rs b/src/main.rs
index a33e963..b93e778 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -24,7 +24,7 @@ fn main() {
 
                 input.clear();
                 stdin().read_line(&mut input).unwrap();
-                match infer(&empty_context, parser::parse_lambda(&input).unwrap()) {
+                match empty_context.infer(parser::parse_lambda(&input).unwrap()) {
                     Ok(kind) => println!("infers! {}", kind),
                     Err(e) => println!("{:?}", e),
                 }
@@ -36,10 +36,10 @@ fn main() {
 
                 input.clear();
                 stdin().read_line(&mut input).unwrap();
-                let kind = infer(&empty_context, parser::parse_lambda(&input).unwrap());
+                let kind = empty_context.infer(parser::parse_lambda(&input).unwrap());
                 match kind {
                     Ok(kind) => {
-                        match check(&empty_context, parser::parse_lambda(&input).unwrap(), &kind) {
+                        match empty_context.check(parser::parse_lambda(&input).unwrap(), &kind) {
                             Ok(_) => println!("checks!"),
                             Err(e) => println!("{:?}", e),
                         }
@@ -54,7 +54,7 @@ fn main() {
 
                 input.clear();
                 stdin().read_line(&mut input).unwrap();
-                match execute(&empty_context, parser::parse_lambda(&input).unwrap()) {
+                match empty_context.execute(parser::parse_lambda(&input).unwrap()) {
                     Ok(term) => println!("{}", term),
                     Err(e) => println!("{:?}", e)
                 }
diff --git a/src/parser.rs b/src/parser.rs
index d3895a4..298e09d 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -2,7 +2,7 @@ use crate::ast::*;
 use multipeek::multipeek;
 
 /// Parses a lambda-calculus-like language into an AST.
-pub fn parse_lambda(input: &str) -> Result<Expression, peg::error::ParseError<peg::str::LineCol>> {
+pub fn parse_lambda(input: &str) -> Result<Expression> {
     // this is kinda awful, i miss my simple nim pegs
     peg::parser! {
         grammar lambda() for str {
@@ -98,7 +98,7 @@ pub fn parse_lambda(input: &str) -> Result<Expression, peg::error::ParseError<pe
             }
         }
     }
-    return lambda::expr(input.trim());
+    return Ok(lambda::expr(input.trim())?);
 }
 
 const operators: [char; 17] =
@@ -115,15 +115,15 @@ pub enum Token {
     Value(String),
     Char(char),
     String(String),
-    Comment(String),
-    Token(String), // catch-all
+    Comment(String), // unused tbh
+    // Token(String), // catch-all
     ScopeBegin, // {
     ScopeEnd,   // }
     ExprEnd,    // ;
 }
 
 /// Properly lexes a whitespace-oriented language into a series of tokens.
-pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
+pub fn lex(input: &str) -> Result<Vec<Token>> {
     enum State {
         Default,
         Char,
@@ -142,6 +142,7 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
     let mut buffer = String::new();
     let mut result = Vec::new();
 
+    // .next() advances the iterator, .peek() does not
     let mut input = multipeek(input.chars()); // multipeek my beloved
     while let Some(c) = input.next() {
         match state {
@@ -151,9 +152,36 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
                     result.push(parse_token(&buffer)?);
                     buffer.clear();
                 },
-                ' ' => todo!(),
-                '\n' => todo!(),
-                '\t' => return Err("Tabs are not supported!"),
+                ' ' => {
+                    // hmm
+                    todo!()
+                },
+                '\n' => {
+                    if let Some(previous) = result.last() {
+                        match previous {
+                            // same scope, no seperator
+                            Token::Operator(_) => (),
+                            // do we have this tbh????
+                            Token::Keyword(_) => return Err("lines shouldn't end with a keyword i think".into()),
+                            // i think uhh
+                            Token::Identifier(_) | Token::Value(_) | Token::Char(_) | Token::String(_) =>
+                                result.push(Token::ExprEnd),
+                            // always scope??
+                            Token::Separator(_) => result.push(Token::ScopeBegin),
+                            // idk
+                            Token::Comment(_) | Token::ScopeBegin | Token::ScopeEnd | Token::ExprEnd =>
+                                return Err("uhh idk always scope lol".into()),
+                        }
+                    }
+                    todo!()
+                },
+                '\t' => return Err("Tabs are not supported!".into()),
+                _ if indent.blank => {
+                    indent.blank = false;
+                    // indentation check
+                    todo!();
+                    buffer.push(c);
+                },
                 '\'' => {
                     result.push(parse_token(&buffer)?);
                     buffer.clear();
@@ -187,12 +215,6 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
                         indent.blank = false;
                     }
                 }
-                _ if indent.blank => {
-                    indent.blank = false;
-                    // indentation check
-                    todo!();
-                    buffer.push(c);
-                }
                 _ => buffer.push(c)
             },
             State::Char => match c {
@@ -205,11 +227,11 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
                         Some('t') => result.push(Token::Char('\t')),
                         Some('\"') => result.push(Token::Char('\"')),
                         Some('\'') => result.push(Token::Char('\'')),
-                        _ => return Err("Invalid string escape sequence!"),
+                        _ => return Err("Invalid string escape sequence!".into()),
                     }
                     state = State::Default;
                     if input.next() != Some('\'') {
-                        return Err("Invalid character sequence!")
+                        return Err("Invalid character sequence!".into())
                     }
                 },
                 '\'' => {
@@ -220,7 +242,7 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
                     result.push(Token::Char(c));
                     state = State::Default;
                     if input.next() != Some('\'') {
-                        return Err("Invalid character sequence!")
+                        return Err("Invalid character sequence!".into())
                     }
                 }
             },
@@ -233,7 +255,7 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
                     Some('t') => buffer.push('\t'),
                     Some('\"') => buffer.push('\"'),
                     Some('\'') => buffer.push('\''),
-                    _ => return Err("Invalid string escape sequence!"),
+                    _ => return Err("Invalid string escape sequence!".into()),
                 },
                 '\"' => {
                     state = State::Default;
@@ -255,7 +277,8 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
             State::Comment => match c {
                 '\n' => {
                     state = State::Default;
-                    result.push(Token::Comment(buffer.to_string()));
+                    // result.push(Token::Comment(buffer.to_string()));
+                    buffer.clear();
                 },
                 _ => buffer.push(c)
             },
@@ -264,7 +287,7 @@ pub fn lex(input: &str) -> Result<Vec<Token>, &'static str> {
     return Ok(result);
 }
 
-fn parse_token(token: &str) -> Result<Token, &'static str> {
+fn parse_token(token: &str) -> Result<Token> {
     if keywords.contains(&token) {
         Ok(Token::Keyword(token.to_string()))
     } else if is_operator(token) {
@@ -274,7 +297,7 @@ fn parse_token(token: &str) -> Result<Token, &'static str> {
     } else if is_identifier(token) {
         Ok(Token::Identifier(token.to_string()))
     } else {
-        Err("Could not parse token!")
+        Err("Could not parse token!".into())
     }
 }
 
diff --git a/src/simple.rs b/src/simple.rs
index 8d87dbf..e763221 100644
--- a/src/simple.rs
+++ b/src/simple.rs
@@ -1,32 +1,33 @@
 use crate::ast::*;
 
-/// Evaluates an expression given a context (of variables) to a term, or fails.
-pub fn execute(context: &Context, expression: Expression) -> Result<Term, String> {
-    match expression {
-        Expression::Annotation { expr, .. } => execute(context, *expr),
-        Expression::Constant { term } => Ok(term),
-        Expression::Variable { id } => match context.get(&id) {
-            Some(term) => Ok(term.clone()),
-            None => Err(format!("no such variable in context {context:?}"))
-        },
-        Expression::Abstraction { param, func } =>
-            Err(format!("attempting to execute an abstraction ({}){}", param, func)),
-        Expression::Application { func, arg } => match *func {
-            Expression::Abstraction { param, func } => {
-                let value = execute(context, *arg)?;
-                let mut context = context.clone();
-                context.insert(param, value);
-                return execute(&context, *func);
-            }
-            _ => Err(format!("attempting to execute an application to non-abstraction {}", *func))
-        },
-        Expression::Conditional { if_cond, if_then, if_else } => {
-            match execute(context, *if_cond)? {
-                Term::Boolean(true) => execute(context, *if_then),
-                Term::Boolean(false) => execute(context, *if_else),
-                term => Err(format!("invalid type {} for a conditional", convert(&term)?))
+impl Context {
+    /// Evaluates an expression given a context (of variables) to a term, or fails.
+    pub fn execute(&self, expression: Expression) -> Result<Term> {
+        match expression {
+            Expression::Annotation { expr, .. } => self.execute(*expr),
+            Expression::Constant { term } => Ok(term),
+            Expression::Variable { id } => match self.get(&id) {
+                Some(term) => Ok(term.clone()),
+                None => Err(format!("no such variable in context {self:?}").into())
+            },
+            Expression::Abstraction { param, func } =>
+                Err(format!("attempting to execute an abstraction ({}){}", param, func).into()),
+            Expression::Application { func, arg } => match *func {
+                Expression::Abstraction { param, func } => {
+                    let value = self.execute(*arg)?;
+                    let mut context = self.clone();
+                    context.insert(param, value);
+                    return context.execute(*func);
+                }
+                _ => Err(format!("attempting to execute an application to non-abstraction {}", *func).into())
+            },
+            Expression::Conditional { if_cond, if_then, if_else } => {
+                match self.execute(*if_cond)? {
+                    Term::Boolean(true) => self.execute(*if_then),
+                    Term::Boolean(false) => self.execute(*if_else),
+                    term => Err(format!("invalid type {} for a conditional", &term.convert()?).into())
+                }
             }
         }
     }
 }
-
diff --git a/src/util.rs b/src/util.rs
index a27f32c..39ac263 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -74,6 +74,6 @@ pub fn Str(len: usize, cap: usize, data: Vec<usize>) -> Term {
     return Term::String { len, cap, data }
 }
 
-pub fn Enum(val: usize, data: Term) -> Term {
-    return Term::Enum { val, data: Box::new(data) }
+pub fn Union(val: usize, data: Term) -> Term {
+    return Term::Union { val, data: Box::new(data) }
 }
diff --git a/tests/test_checking.rs b/tests/test_checking.rs
index e553a4e..b0f4140 100644
--- a/tests/test_checking.rs
+++ b/tests/test_checking.rs
@@ -32,15 +32,15 @@ fn test_parsing_succeeds() {
 #[test]
 fn test_inference() {
     let context = Context::new();
-    assert_eq!(infer(&context, parse_lambda(sanity_check).unwrap()), Ok(Int));
-    assert_eq!(infer(&context, parse_lambda(negate).unwrap()), Ok(Func(Bool, Bool)));
-    assert_eq!(infer(&context, parse_lambda(basic_abstraction).unwrap()), Ok(Func(Int, Int)));
-    assert_eq!(infer(&context, parse_lambda(basic_application).unwrap()), Ok(Int));
-    assert_eq!(infer(&context, parse_lambda(correct_cond_abs).unwrap()), Ok(Func(Bool, Int)));
-    assert_eq!(infer(&context, parse_lambda(correct_cond).unwrap()), Ok(Nat));
-    assert!(infer(&context, parse_lambda(not_inferrable).unwrap()).is_err());
-    assert!(infer(&context, parse_lambda(incorrect_branches).unwrap()).is_err());
-    assert!(infer(&context, parse_lambda(incorrect_cond_abs).unwrap()).is_err());
+    assert_eq!(context.infer(parse_lambda(sanity_check).unwrap()).unwrap(), Int);
+    assert_eq!(context.infer(parse_lambda(negate).unwrap()).unwrap(), Func(Bool, Bool));
+    assert_eq!(context.infer(parse_lambda(basic_abstraction).unwrap()).unwrap(), Func(Int, Int));
+    assert_eq!(context.infer(parse_lambda(basic_application).unwrap()).unwrap(), Int);
+    assert_eq!(context.infer(parse_lambda(correct_cond_abs).unwrap()).unwrap(), Func(Bool, Int));
+    assert_eq!(context.infer(parse_lambda(correct_cond).unwrap()).unwrap(), Nat);
+    assert!(context.infer(parse_lambda(not_inferrable).unwrap()).is_err());
+    assert!(context.infer(parse_lambda(incorrect_branches).unwrap()).is_err());
+    assert!(context.infer(parse_lambda(incorrect_cond_abs).unwrap()).is_err());
 }
 
 #[test]
@@ -48,17 +48,17 @@ fn test_checking() {
     let context = Context::new();
 
     // uninteresting
-    assert!(check(&context, parse_lambda(sanity_check).unwrap(), &Int).is_ok());
-    assert!(check(&context, parse_lambda(negate).unwrap(), &Func(Bool, Bool)).is_ok());
-    assert!(check(&context, parse_lambda(basic_abstraction).unwrap(), &Func(Int, Int)).is_ok());
-    assert!(check(&context, parse_lambda(basic_application).unwrap(), &Int).is_ok());
-    assert!(check(&context, parse_lambda(correct_cond_abs).unwrap(), &Func(Bool, Int)).is_ok());
-    assert!(check(&context, parse_lambda(correct_cond).unwrap(), &Nat).is_ok());
-    assert!(check(&context, parse_lambda(incorrect_branches).unwrap(), &Unit).is_err());
-    assert!(check(&context, parse_lambda(incorrect_cond_abs).unwrap(), &Error).is_err());
+    assert!(context.check(parse_lambda(sanity_check).unwrap(), &Int).is_ok());
+    assert!(context.check(parse_lambda(negate).unwrap(), &Func(Bool, Bool)).is_ok());
+    assert!(context.check(parse_lambda(basic_abstraction).unwrap(), &Func(Int, Int)).is_ok());
+    assert!(context.check(parse_lambda(basic_application).unwrap(), &Int).is_ok());
+    assert!(context.check(parse_lambda(correct_cond_abs).unwrap(), &Func(Bool, Int)).is_ok());
+    assert!(context.check(parse_lambda(correct_cond).unwrap(), &Nat).is_ok());
+    assert!(context.check(parse_lambda(incorrect_branches).unwrap(), &Unit).is_err());
+    assert!(context.check(parse_lambda(incorrect_cond_abs).unwrap(), &Error).is_err());
 
     // more fun
-    assert!(check(&context, parse_lambda(not_inferrable).unwrap(), &Func(Bool, Func(Int, Func(Int, Int)))).is_ok());
-    assert!(check(&context, parse_lambda(not_inferrable).unwrap(), &Func(Bool, Func(Nat, Func(Nat, Nat)))).is_ok());
-    assert!(check(&context, parse_lambda(not_inferrable).unwrap(), &Func(Bool, Func(Unit, Func(Unit, Unit)))).is_ok());
+    assert!(context.check(parse_lambda(not_inferrable).unwrap(), &Func(Bool, Func(Int, Func(Int, Int)))).is_ok());
+    assert!(context.check(parse_lambda(not_inferrable).unwrap(), &Func(Bool, Func(Nat, Func(Nat, Nat)))).is_ok());
+    assert!(context.check(parse_lambda(not_inferrable).unwrap(), &Func(Bool, Func(Unit, Func(Unit, Unit)))).is_ok());
 }
diff --git a/tests/test_execution.rs b/tests/test_execution.rs
index d9b1c5e..44df5ae 100644
--- a/tests/test_execution.rs
+++ b/tests/test_execution.rs
@@ -5,10 +5,10 @@ use chrysanthemum::util::*;
 #[test]
 fn test_simple() {
     let context = Context::new();
-    assert_eq!(execute(&context, Const(Term::Boolean(false))), Ok(Term::Boolean(false)));
-    assert_eq!(execute(&context, Const(Term::Natural(123))), Ok(Term::Natural(123)));
-    assert_eq!(execute(&context, Const(Term::Integer(123))), Ok(Term::Integer(123)));
-    assert!(execute(&context, Var("x")).is_err());
+    assert_eq!(context.execute(Const(Term::Boolean(false))).unwrap(), Term::Boolean(false));
+    assert_eq!(context.execute(Const(Term::Natural(123))).unwrap(), Term::Natural(123));
+    assert_eq!(context.execute(Const(Term::Integer(123))).unwrap(), Term::Integer(123));
+    assert!(context.execute(Var("x")).is_err());
 }
 
 #[test]
@@ -16,8 +16,9 @@ fn test_complex() {
     let mut context = Context::new();
     context.insert(String::from("x"), Term::Natural(413));
     context.insert(String::from("y"), Term::Boolean(true));
-    assert_eq!(execute(&context, Var("x")), Ok(Term::Natural(413)));
-    assert_eq!(execute(&context, Cond(Var("y"), Const(Term::Integer(612)), Var("x"))), Ok(Term::Integer(612)));
-    assert_eq!(execute(&context,
-        App(Abs("z", Cond(Const(Term::Boolean(false)), Var("x"), Var("z"))), Const(Term::Integer(1025)))), Ok(Term::Integer(1025)));
+    assert_eq!(context.execute(Var("x")).unwrap(), Term::Natural(413));
+    assert_eq!(context.execute(Cond(Var("y"), Const(Term::Integer(612)),
+        Var("x"))).unwrap(), Term::Integer(612));
+    assert_eq!(context.execute(App(Abs("z", Cond(Const(Term::Boolean(false)),
+        Var("x"), Var("z"))), Const(Term::Integer(1025)))).unwrap(), Term::Integer(1025));
 }
diff --git a/tests/test_parser.rs b/tests/test_parser.rs
index 9ac8f32..84f6395 100644
--- a/tests/test_parser.rs
+++ b/tests/test_parser.rs
@@ -6,9 +6,9 @@ use chrysanthemum::util::*;
 
 #[test]
 fn test_simple_phrases() {
-    assert_eq!(parse_lambda("-123"), Ok(Const(Term::Integer(-123))));
-    assert_eq!(parse_lambda("x12"), Ok(Var("x12")));
-    assert_eq!(parse_lambda("x12x2"), Ok(Var("x12x2")));
+    assert_eq!(parse_lambda("-123").unwrap(), Const(Term::Integer(-123)));
+    assert_eq!(parse_lambda("x12").unwrap(), Var("x12"));
+    assert_eq!(parse_lambda("x12x2").unwrap(), Var("x12x2"));
     // so i _don't_ want these to be valid identifiers:
     // but i actually have no idea why my peg is rejecting them lmao
     assert!(parse_lambda("12x").is_err());
@@ -17,36 +17,36 @@ fn test_simple_phrases() {
 
 #[test]
 fn test_simple_annotations() {
-    assert_eq!(parse_lambda("t: int"), Ok(Ann(Var("t"), Int)));
-    assert_eq!(parse_lambda("12: nat"), Ok(Ann(Const(Term::Natural(12)), Nat)));
+    assert_eq!(parse_lambda("t: int").unwrap(), Ann(Var("t"), Int));
+    assert_eq!(parse_lambda("12: nat").unwrap(), Ann(Const(Term::Natural(12)), Nat));
     assert!(parse_lambda("t: fake").is_err());
 }
 
 #[test]
 fn test_simple_expressions() {
-    assert_eq!(parse_lambda("λx.y"), Ok(Abs("x", Var("y"))));
-    assert_eq!(parse_lambda("λ x.y"), Ok(Abs("x", Var("y"))));
-    assert_eq!(parse_lambda("λx.y"), Ok(Abs("x", Var("y"))));
-    assert_eq!(parse_lambda("lambda x . y"), Ok(Abs("x", Var("y"))));
-    assert_eq!(parse_lambda("(λx.y)"), Ok(Abs("x", Var("y"))));
-    assert_eq!(parse_lambda("(λx.y) x"), Ok(App(Abs("x", Var("y")), Var("x"))));
-    assert_eq!(parse_lambda("(λx.y) x"), Ok(App(Abs("x", Var("y")), Var("x"))));
-    assert_eq!(parse_lambda("if x then y else z"), Ok(Cond(Var("x"), Var("y"), Var("z"))));
-    assert_eq!(parse_lambda("if xeme then yak else zebra"), Ok(Cond(Var("xeme"), Var("yak"), Var("zebra"))));
-    assert_eq!(parse_lambda("if 413 then 612 else 1025"), Ok(Cond(Const(Term::Natural(413)), Const(Term::Natural(612)), Const(Term::Natural(1025))))); // invalid, but should parse
+    assert_eq!(parse_lambda("λx.y").unwrap(), Abs("x", Var("y")));
+    assert_eq!(parse_lambda("λ x.y").unwrap(), Abs("x", Var("y")));
+    assert_eq!(parse_lambda("λx.y").unwrap(), Abs("x", Var("y")));
+    assert_eq!(parse_lambda("lambda x . y").unwrap(), Abs("x", Var("y")));
+    assert_eq!(parse_lambda("(λx.y)").unwrap(), Abs("x", Var("y")));
+    assert_eq!(parse_lambda("(λx.y) x").unwrap(), App(Abs("x", Var("y")), Var("x")));
+    assert_eq!(parse_lambda("(λx.y) x").unwrap(), App(Abs("x", Var("y")), Var("x")));
+    assert_eq!(parse_lambda("if x then y else z").unwrap(), Cond(Var("x"), Var("y"), Var("z")));
+    assert_eq!(parse_lambda("if xeme then yak else zebra").unwrap(), Cond(Var("xeme"), Var("yak"), Var("zebra")));
+    assert_eq!(parse_lambda("if 413 then 612 else 1025").unwrap(), Cond(Const(Term::Natural(413)), Const(Term::Natural(612)), Const(Term::Natural(1025)))); // invalid, but should parse
 }
 
 #[test]
 fn test_complex_expressions() {
-    assert_eq!(parse_lambda("(λy.if y then false else true) z"), Ok(App(Abs("y", Cond(Var("y"), Const(Term::Boolean(false)), Const(Term::Boolean(true)))), Var("z"))));
+    assert_eq!(parse_lambda("(λy.if y then false else true) z").unwrap(), App(Abs("y", Cond(Var("y"), Const(Term::Boolean(false)), Const(Term::Boolean(true)))), Var("z")));
 }
 
 #[test]
 fn test_complex_annotations() {
-    assert_eq!(parse_lambda("(lambda x . y)  : int"), Ok(Ann(Abs("x", Var("y")), Int)));
-    assert_eq!(parse_lambda("((lambda x. y): (int -> int)) -413: int"), Ok(App(Ann(Abs("x", Var("y")), Func(Int, Int) ), Ann(Const(Term::Integer(-413)), Int))));
-    assert_eq!(parse_lambda("if false: bool then true: bool else 2: int"), Ok(Cond(Ann(Const(Term::Boolean(false)), Bool), Ann(Const(Term::Boolean(true)), Bool), Ann(Const(Term::Natural(2)), Int))));
-    assert_eq!(parse_lambda("(lambda x. if x then true: bool else false: bool): (int -> bool)"), Ok(Ann(Abs("x", Cond(Var("x"), Ann(Const(Term::Boolean(true)), Bool), Ann(Const(Term::Boolean(false)), Bool))), Func(Int, Bool))));
-    assert_eq!(parse_lambda("(lambda x. if x then 1: int else 0: int): (bool -> int)"), Ok(Ann(Abs("x", Cond(Var("x"), Ann(Const(Term::Natural(1)), Int), Ann(Const(Term::Natural(0)), Int))), Func(Bool, Int))));
-    assert_eq!(parse_lambda("(lambda x. if x then false else true): (bool -> bool)"), Ok(Ann(Abs("x", Cond(Var("x"), Const(Term::Boolean(false)), Const(Term::Boolean(true)))), Func(Bool, Bool))));
+    assert_eq!(parse_lambda("(lambda x . y)  : int").unwrap(), Ann(Abs("x", Var("y")), Int));
+    assert_eq!(parse_lambda("((lambda x. y): (int -> int)) -413: int").unwrap(), App(Ann(Abs("x", Var("y")), Func(Int, Int) ), Ann(Const(Term::Integer(-413)), Int)));
+    assert_eq!(parse_lambda("if false: bool then true: bool else 2: int").unwrap(), Cond(Ann(Const(Term::Boolean(false)), Bool), Ann(Const(Term::Boolean(true)), Bool), Ann(Const(Term::Natural(2)), Int)));
+    assert_eq!(parse_lambda("(lambda x. if x then true: bool else false: bool): (int -> bool)").unwrap(), Ann(Abs("x", Cond(Var("x"), Ann(Const(Term::Boolean(true)), Bool), Ann(Const(Term::Boolean(false)), Bool))), Func(Int, Bool)));
+    assert_eq!(parse_lambda("(lambda x. if x then 1: int else 0: int): (bool -> int)").unwrap(), Ann(Abs("x", Cond(Var("x"), Ann(Const(Term::Natural(1)), Int), Ann(Const(Term::Natural(0)), Int))), Func(Bool, Int)));
+    assert_eq!(parse_lambda("(lambda x. if x then false else true): (bool -> bool)").unwrap(), Ann(Abs("x", Cond(Var("x"), Const(Term::Boolean(false)), Const(Term::Boolean(true)))), Func(Bool, Bool)));
 }