examples/basic/type_checker1.ngr

@@ -0,0 +1,6 @@
+x = 1 + 1u16;
+print x;
+y = 1u16 + 1;
+print y;
+z = 1 + 1 + 1;
+print z;

src/eval/primtype.rs

@@ -4,7 +4,7 @@ use crate::{
 };
 use std::{fmt::Display, str::FromStr};
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum PrimitiveType {
     U8,
     U16,
@@ -83,56 +83,39 @@ impl PrimitiveType {
     /// Return true if this type can be safely cast into the target type.
     pub fn can_cast_to(&self, target: &PrimitiveType) -> bool {
         match self {
-            PrimitiveType::U8 => match target {
-                PrimitiveType::U8 => true,
-                PrimitiveType::U16 => true,
-                PrimitiveType::U32 => true,
-                PrimitiveType::U64 => true,
-                PrimitiveType::I16 => true,
-                PrimitiveType::I32 => true,
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
-            PrimitiveType::U16 => match target {
-                PrimitiveType::U16 => true,
-                PrimitiveType::U32 => true,
-                PrimitiveType::U64 => true,
-                PrimitiveType::I32 => true,
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
-            PrimitiveType::U32 => match target {
-                PrimitiveType::U32 => true,
-                PrimitiveType::U64 => true,
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
-            PrimitiveType::U64 => match target {
-                PrimitiveType::U64 => true,
-                _ => false,
-            },
-            PrimitiveType::I8 => match target {
-                PrimitiveType::I8 => true,
-                PrimitiveType::I16 => true,
-                PrimitiveType::I32 => true,
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
-            PrimitiveType::I16 => match target {
-                PrimitiveType::I16 => true,
-                PrimitiveType::I32 => true,
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
-            PrimitiveType::I32 => match target {
-                PrimitiveType::I32 => true,
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
-            PrimitiveType::I64 => match target {
-                PrimitiveType::I64 => true,
-                _ => false,
-            },
+            PrimitiveType::U8 => matches!(
+                target,
+                PrimitiveType::U8
+                    | PrimitiveType::U16
+                    | PrimitiveType::U32
+                    | PrimitiveType::U64
+                    | PrimitiveType::I16
+                    | PrimitiveType::I32
+                    | PrimitiveType::I64
+            ),
+            PrimitiveType::U16 => matches!(
+                target,
+                PrimitiveType::U16
+                    | PrimitiveType::U32
+                    | PrimitiveType::U64
+                    | PrimitiveType::I32
+                    | PrimitiveType::I64
+            ),
+            PrimitiveType::U32 => matches!(
+                target,
+                PrimitiveType::U32 | PrimitiveType::U64 | PrimitiveType::I64
+            ),
+            PrimitiveType::U64 => target == &PrimitiveType::U64,
+            PrimitiveType::I8 => matches!(
+                target,
+                PrimitiveType::I8 | PrimitiveType::I16 | PrimitiveType::I32 | PrimitiveType::I64
+            ),
+            PrimitiveType::I16 => matches!(
+                target,
+                PrimitiveType::I16 | PrimitiveType::I32 | PrimitiveType::I64
+            ),
+            PrimitiveType::I32 => matches!(target, PrimitiveType::I32 | PrimitiveType::I64),
+            PrimitiveType::I64 => target == &PrimitiveType::I64,
         }
     }
 
@@ -174,4 +157,17 @@ impl PrimitiveType {
             }),
         }
     }
+
+    pub fn max_value(&self) -> u64 {
+        match self {
+            PrimitiveType::U8 => u8::MAX as u64,
+            PrimitiveType::U16 => u16::MAX as u64,
+            PrimitiveType::U32 => u32::MAX as u64,
+            PrimitiveType::U64 => u64::MAX,
+            PrimitiveType::I8 => i8::MAX as u64,
+            PrimitiveType::I16 => i16::MAX as u64,
+            PrimitiveType::I32 => i32::MAX as u64,
+            PrimitiveType::I64 => i64::MAX as u64,
+        }
+    }
 }

src/ir/ast.rs

@@ -3,7 +3,7 @@ use crate::{
     syntax::{self, ConstantType, Location},
 };
 use internment::ArcIntern;
-use pretty::{DocAllocator, Pretty};
+use pretty::{BoxAllocator, DocAllocator, Pretty};
 use proptest::{
     prelude::Arbitrary,
     strategy::{BoxedStrategy, Strategy},
@@ -224,6 +224,12 @@ where
     }
 }
 
+impl fmt::Display for Primitive {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        <&Primitive as Pretty<'_, BoxAllocator, ()>>::pretty(self, &BoxAllocator).render_fmt(72, f)
+    }
+}
+
 /// An expression that is always either a value or a reference.
 ///
 /// This is the type used to guarantee that we don't nest expressions

src/ir/type_infer.rs

@@ -21,13 +21,23 @@ impl syntax::Program {
         let program = convert_program(self, &mut constraint_db);
         let inference_result = solve_constraints(constraint_db);
 
-        inference_result.map(|type_renames| finalize_program(program, type_renames))
+        inference_result.map(|resolutions| finalize_program(program, &resolutions))
     }
 }
 
 proptest::proptest! {
     #[test]
     fn translation_maintains_semantics(input: syntax::Program) {
+            use pretty::{DocAllocator, Pretty};
+            let allocator = pretty::BoxAllocator;
+            allocator
+              .text("---------------")
+              .append(allocator.hardline())
+              .append(input.pretty(&allocator))
+              .1
+              .render_colored(70, pretty::termcolor::StandardStream::stdout(pretty::termcolor::ColorChoice::Auto))
+              .expect("rendering works");
+
         let syntax_result = input.eval();
         let ir = input.type_infer().expect("arbitrary should generate type-safe programs");
         let ir_result = ir.eval();

src/ir/type_infer/ast.rs

@@ -109,7 +109,7 @@ where
 /// a primitive), any subexpressions have been bound to variables so
 /// that the referenced data will always either be a constant or a
 /// variable reference.
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 pub enum Expression {
     Atomic(ValueOrRef),
     Cast(Location, Type, ValueOrRef),
@@ -177,7 +177,7 @@ where
 /// This is the type used to guarantee that we don't nest expressions
 /// at this level. Instead, expressions that take arguments take one
 /// of these, which can only be a constant or a reference.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum ValueOrRef {
     Value(Location, Type, Value),
     Ref(Location, Type, ArcIntern<String>),
@@ -208,7 +208,7 @@ impl From<ValueOrRef> for Expression {
 /// user to input the number. By retaining it, we can ensure that if we need
 /// to print the number back out, we can do so in the form that the user
 /// entered it.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum Value {
     Unknown(Option<u8>, u64),
     I8(Option<u8>, i8),
@@ -273,6 +273,12 @@ pub enum Type {
     Primitive(PrimitiveType),
 }
 
+impl Type {
+    pub fn is_concrete(&self) -> bool {
+        !matches!(self, Type::Variable(_, _))
+    }
+}
+
 impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Type
 where
     A: 'a,
@@ -321,10 +327,10 @@ pub fn gensym(name: &str) -> ArcIntern<String> {
 pub fn gentype() -> Type {
     static COUNTER: AtomicUsize = AtomicUsize::new(0);
 
-    let new_name = ArcIntern::new(format!(
+    let name = ArcIntern::new(format!(
         "t<{}>",
         COUNTER.fetch_add(1, std::sync::atomic::Ordering::SeqCst)
     ));
 
-    Type::Variable(Location::manufactured(), new_name)
+    Type::Variable(Location::manufactured(), name)
 }

src/ir/type_infer/convert.rs

@@ -149,7 +149,11 @@ fn convert_expression(
                     ),
                 };
 
-                constraint_db.push(Constraint::FitsInNumType(loc.clone(), newtype.clone(), value));
+                constraint_db.push(Constraint::FitsInNumType(
+                    loc.clone(),
+                    newtype.clone(),
+                    value,
+                ));
                 (
                     vec![],
                     ir::Expression::Atomic(ir::ValueOrRef::Value(loc, newtype.clone(), newval)),
@@ -230,3 +234,126 @@ fn simplify_expr(expr: ir::Expression, stmts: &mut Vec<ir::Statement>) -> ir::Va
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::syntax::Location;
+
+    fn one() -> syntax::Expression {
+        syntax::Expression::Value(
+            Location::manufactured(),
+            syntax::Value::Number(None, None, 1),
+        )
+    }
+
+    fn vec_contains<T, F: Fn(&T) -> bool>(x: &[T], f: F) -> bool {
+        for x in x.iter() {
+            if f(x) {
+                return true;
+            }
+        }
+        false
+    }
+
+    fn infer_expression(
+        x: syntax::Expression,
+    ) -> (ir::Expression, Vec<ir::Statement>, Vec<Constraint>, Type) {
+        let mut constraints = Vec::new();
+        let renames = HashMap::new();
+        let mut bindings = HashMap::new();
+        let (stmts, expr, ty) = convert_expression(x, &mut constraints, &renames, &mut bindings);
+        (expr, stmts, constraints, ty)
+    }
+
+    fn infer_statement(x: syntax::Statement) -> (Vec<ir::Statement>, Vec<Constraint>) {
+        let mut constraints = Vec::new();
+        let mut renames = HashMap::new();
+        let mut bindings = HashMap::new();
+        let res = convert_statement(x, &mut constraints, &mut renames, &mut bindings);
+        (res, constraints)
+    }
+
+    #[test]
+    fn constant_one() {
+        let (expr, stmts, constraints, ty) = infer_expression(one());
+        assert!(stmts.is_empty());
+        assert!(matches!(
+            expr,
+            ir::Expression::Atomic(ir::ValueOrRef::Value(_, _, ir::Value::Unknown(None, 1)))
+        ));
+        assert!(vec_contains(&constraints, |x| matches!(
+            x,
+            Constraint::FitsInNumType(_, _, 1)
+        )));
+        assert!(vec_contains(
+            &constraints,
+            |x| matches!(x, Constraint::NumericType(_, t) if t == &ty)
+        ));
+    }
+
+    #[test]
+    fn one_plus_one() {
+        let opo = syntax::Expression::Primitive(
+            Location::manufactured(),
+            "+".to_string(),
+            vec![one(), one()],
+        );
+        let (expr, stmts, constraints, ty) = infer_expression(opo);
+        assert!(stmts.is_empty());
+        assert!(matches!(expr, ir::Expression::Primitive(_, t, ir::Primitive::Plus, _) if t == ty));
+        assert!(vec_contains(&constraints, |x| matches!(
+            x,
+            Constraint::FitsInNumType(_, _, 1)
+        )));
+        assert!(vec_contains(
+            &constraints,
+            |x| matches!(x, Constraint::NumericType(_, t) if t != &ty)
+        ));
+        assert!(vec_contains(
+            &constraints,
+            |x| matches!(x, Constraint::ProperPrimitiveArgs(_, ir::Primitive::Plus, args, ret) if args.len() == 2 && ret == &ty)
+        ));
+    }
+
+    #[test]
+    fn one_plus_one_plus_one() {
+        let stmt = syntax::Statement::parse(1, "x = 1 + 1 + 1;").expect("basic parse");
+        let (stmts, constraints) = infer_statement(stmt);
+        assert_eq!(stmts.len(), 2);
+        let ir::Statement::Binding(_args, name1, temp_ty1, ir::Expression::Primitive(_, primty1, ir::Primitive::Plus, primargs1)) = stmts.get(0).expect("item two") else {
+            panic!("Failed to match first statement");
+        };
+        let ir::Statement::Binding(_args, name2, temp_ty2, ir::Expression::Primitive(_, primty2, ir::Primitive::Plus, primargs2)) = stmts.get(1).expect("item two") else {
+            panic!("Failed to match second statement");
+        };
+        let &[ir::ValueOrRef::Value(_, ref left1ty, _), ir::ValueOrRef::Value(_, ref right1ty, _)] = &primargs1[..] else {
+            panic!("Failed to match first arguments");
+        };
+        let &[ir::ValueOrRef::Ref(_, _, ref left2name), ir::ValueOrRef::Value(_, ref right2ty, _)] = &primargs2[..] else {
+            panic!("Failed to match first arguments");
+        };
+        assert_ne!(name1, name2);
+        assert_ne!(temp_ty1, temp_ty2);
+        assert_ne!(primty1, primty2);
+        assert_eq!(name1, left2name);
+        assert!(vec_contains(
+            &constraints,
+            |x| matches!(x, Constraint::NumericType(_, t) if t == left1ty)
+        ));
+        assert!(vec_contains(
+            &constraints,
+            |x| matches!(x, Constraint::NumericType(_, t) if t == right1ty)
+        ));
+        assert!(vec_contains(
+            &constraints,
+            |x| matches!(x, Constraint::NumericType(_, t) if t == right2ty)
+        ));
+        for (i, s) in stmts.iter().enumerate() {
+            println!("{}: {:?}", i, s);
+        }
+        for (i, c) in constraints.iter().enumerate() {
+            println!("{}: {:?}", i, c);
+        }
+    }
+}

src/ir/type_infer/finalize.rs

@@ -1,88 +1,80 @@
-use super::ast as input;
+use super::{ast as input, solve::TypeResolutions};
 use crate::{eval::PrimitiveType, ir as output};
-use internment::ArcIntern;
-use std::collections::HashMap;
 
 pub fn finalize_program(
     mut program: input::Program,
-    type_renames: HashMap<ArcIntern<String>, input::Type>,
+    resolutions: &TypeResolutions,
 ) -> output::Program {
     output::Program {
         statements: program
             .statements
             .drain(..)
-            .map(|x| finalize_statement(x, &type_renames))
+            .map(|x| finalize_statement(x, resolutions))
             .collect(),
     }
 }
 
 fn finalize_statement(
     statement: input::Statement,
-    type_renames: &HashMap<ArcIntern<String>, input::Type>,
+    resolutions: &TypeResolutions,
 ) -> output::Statement {
     match statement {
         input::Statement::Binding(loc, var, ty, expr) => output::Statement::Binding(
             loc,
             var,
-            finalize_type(ty, type_renames),
-            finalize_expression(expr, type_renames),
+            finalize_type(ty, resolutions),
+            finalize_expression(expr, resolutions),
         ),
         input::Statement::Print(loc, ty, var) => {
-            output::Statement::Print(loc, finalize_type(ty, type_renames), var)
+            output::Statement::Print(loc, finalize_type(ty, resolutions), var)
         }
     }
 }
 
 fn finalize_expression(
     expression: input::Expression,
-    type_renames: &HashMap<ArcIntern<String>, input::Type>,
+    resolutions: &TypeResolutions,
 ) -> output::Expression {
     match expression {
         input::Expression::Atomic(val_or_ref) => {
-            output::Expression::Atomic(finalize_val_or_ref(val_or_ref, type_renames))
+            output::Expression::Atomic(finalize_val_or_ref(val_or_ref, resolutions))
         }
         input::Expression::Cast(loc, target, val_or_ref) => output::Expression::Cast(
             loc,
-            finalize_type(target, type_renames),
-            finalize_val_or_ref(val_or_ref, type_renames),
+            finalize_type(target, resolutions),
+            finalize_val_or_ref(val_or_ref, resolutions),
         ),
         input::Expression::Primitive(loc, ty, prim, mut args) => output::Expression::Primitive(
             loc,
-            finalize_type(ty, type_renames),
+            finalize_type(ty, resolutions),
             prim,
             args.drain(..)
-                .map(|x| finalize_val_or_ref(x, type_renames))
+                .map(|x| finalize_val_or_ref(x, resolutions))
                 .collect(),
         ),
     }
 }
 
-fn finalize_type(
-    ty: input::Type,
-    type_renames: &HashMap<ArcIntern<String>, input::Type>,
-) -> output::Type {
+fn finalize_type(ty: input::Type, resolutions: &TypeResolutions) -> output::Type {
     match ty {
         input::Type::Primitive(x) => output::Type::Primitive(x),
-        input::Type::Variable(loc, name) => match type_renames.get(&name) {
-            Some(input::Type::Primitive(x)) => output::Type::Primitive(*x),
-            res => panic!(
-                "ACK! Internal error cleaning up temporary type name at {:?}: got {:?}",
-                loc, res
-            ),
+        input::Type::Variable(_, tvar) => match resolutions.get(&tvar) {
+            None => panic!("Did not resolve type for type variable {}", tvar),
+            Some(pt) => output::Type::Primitive(*pt),
         },
     }
 }
 
 fn finalize_val_or_ref(
     valref: input::ValueOrRef,
-    type_renames: &HashMap<ArcIntern<String>, input::Type>,
+    resolutions: &TypeResolutions,
 ) -> output::ValueOrRef {
     match valref {
         input::ValueOrRef::Ref(loc, ty, var) => {
-            output::ValueOrRef::Ref(loc, finalize_type(ty, type_renames), var)
+            output::ValueOrRef::Ref(loc, finalize_type(ty, resolutions), var)
         }
         input::ValueOrRef::Value(loc, ty, val) => {
-            let new_type = finalize_type(ty, type_renames);
+            let new_type = finalize_type(ty, resolutions);
 
             match val {
                 input::Value::Unknown(base, value) => match new_type {
@@ -101,11 +93,9 @@ fn finalize_val_or_ref(
                         new_type,
                         output::Value::U32(base, value as u32),
                     ),
-                    output::Type::Primitive(PrimitiveType::U64) => output::ValueOrRef::Value(
-                        loc,
-                        new_type,
-                        output::Value::U64(base, value),
-                    ),
+                    output::Type::Primitive(PrimitiveType::U64) => {
+                        output::ValueOrRef::Value(loc, new_type, output::Value::U64(base, value))
+                    }
                     output::Type::Primitive(PrimitiveType::I8) => output::ValueOrRef::Value(
                         loc,
                         new_type,

src/ir/type_infer/solve.rs

@@ -3,8 +3,9 @@ use super::ast::Type;
 use crate::{eval::PrimitiveType, syntax::Location};
 use codespan_reporting::diagnostic::Diagnostic;
 use internment::ArcIntern;
-use std::collections::HashMap;
+use std::{collections::HashMap, fmt};
 
+#[derive(Debug)]
 pub enum Constraint {
     /// The given type must be printable using the `print` built-in
     Printable(Location, Type),
@@ -14,12 +15,34 @@ pub enum Constraint {
     ProperPrimitiveArgs(Location, ir::Primitive, Vec<Type>, Type),
     /// The given type can be casted to the target type safely
     CanCastTo(Location, Type, Type),
-    /// The given type must be some numeric type
+    /// The given type must be some numeric type, but this is not a constant
+    /// value, so don't try to default it if we can't figure it out
     NumericType(Location, Type),
     /// The two types should be equivalent
     Equivalent(Location, Type, Type),
 }
 
+impl fmt::Display for Constraint {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Constraint::Printable(_, ty) => write!(f, "PRINTABLE {}", ty),
+            Constraint::FitsInNumType(_, ty, num) => write!(f, "FITS_IN {} {}", num, ty),
+            Constraint::ProperPrimitiveArgs(_, op, args, ret) if args.len() == 1 => {
+                write!(f, "PRIM {} {} -> {}", op, args[0], ret)
+            }
+            Constraint::ProperPrimitiveArgs(_, op, args, ret) if args.len() == 2 => {
+                write!(f, "PRIM {} ({}, {}) -> {}", op, args[0], args[1], ret)
+            }
+            Constraint::ProperPrimitiveArgs(_, op, _, ret) => write!(f, "PRIM {} -> {}", op, ret),
+            Constraint::CanCastTo(_, ty, ty2) => write!(f, "CAST {} -> {}", ty, ty2),
+            Constraint::NumericType(_, ty) => write!(f, "NUMERIC {}", ty),
+            Constraint::Equivalent(_, ty, ty2) => write!(f, "EQUIVALENT {} => {}", ty, ty2),
+        }
+    }
+}
+
+pub type TypeResolutions = HashMap<ArcIntern<String>, PrimitiveType>;
+
 pub enum TypeInferenceResult<Result> {
     Success {
         result: Result,
@@ -71,7 +94,66 @@ pub enum TypeInferenceError {
 
 impl From<TypeInferenceError> for Diagnostic<usize> {
     fn from(value: TypeInferenceError) -> Self {
-        unimplemented!()
+        match value {
+            TypeInferenceError::ConstantTooLarge(loc, primty, value) => loc
+                .labelled_error("constant too large for type")
+                .with_message(format!(
+                    "Type {} has a max value of {}, which is smaller than {}",
+                    primty,
+                    primty.max_value(),
+                    value
+                )),
+            TypeInferenceError::NotEquivalent(loc, ty1, ty2) => loc
+                .labelled_error("type inference error")
+                .with_message(format!("Expected type {}, received type {}", ty1, ty2)),
+            TypeInferenceError::CannotSafelyCast(loc, ty1, ty2) => loc
+                .labelled_error("unsafe type cast")
+                .with_message(format!("Cannot safely cast {} to {}", ty1, ty2)),
+            TypeInferenceError::WrongPrimitiveArity(loc, prim, lower, upper, observed) => loc
+                .labelled_error("wrong number of arguments")
+                .with_message(format!(
+                    "expected {} for {}, received {}",
+                    if lower == upper && lower > 1 {
+                        format!("{} arguments", lower)
+                    } else if lower == upper {
+                        format!("{} argument", lower)
+                    } else {
+                        format!("{}-{} arguments", lower, upper)
+                    },
+                    prim,
+                    observed
+                )),
+            TypeInferenceError::CouldNotSolve(Constraint::CanCastTo(loc, a, b)) => {
+                loc.labelled_error("internal error").with_message(format!(
+                    "could not determine if it was safe to cast from {} to {:#?}",
+                    a, b
+                ))
+            }
+            TypeInferenceError::CouldNotSolve(Constraint::Equivalent(loc, a, b)) => {
+                loc.labelled_error("internal error").with_message(format!(
+                    "could not determine if {} and {:#?} were equivalent",
+                    a, b
+                ))
+            }
+            TypeInferenceError::CouldNotSolve(Constraint::FitsInNumType(loc, ty, val)) => {
+                loc.labelled_error("internal error").with_message(format!(
+                    "Could not determine if {} could fit in {}",
+                    val, ty
+                ))
+            }
+            TypeInferenceError::CouldNotSolve(Constraint::NumericType(loc, ty)) => loc
+                .labelled_error("internal error")
+                .with_message(format!("Could not determine if {} was a numeric type", ty)),
+            TypeInferenceError::CouldNotSolve(Constraint::Printable(loc, ty)) => loc
+                .labelled_error("internal error")
+                .with_message(format!("Could not determine if type {} was printable", ty)),
+            TypeInferenceError::CouldNotSolve(Constraint::ProperPrimitiveArgs(loc, prim, _, _)) => {
+                loc.labelled_error("internal error").with_message(format!(
+                    "Could not tell if primitive {} received the proper argument types",
+                    prim
+                ))
+            }
+        }
     }
 }
 
@@ -81,22 +163,31 @@ pub enum TypeInferenceWarning {
 
 impl From<TypeInferenceWarning> for Diagnostic<usize> {
     fn from(value: TypeInferenceWarning) -> Self {
-        unimplemented!()
+        match value {
+            TypeInferenceWarning::DefaultedTo(loc, ty) => Diagnostic::warning()
+                .with_labels(vec![loc.primary_label().with_message("unknown type")])
+                .with_message(format!("Defaulted unknown type to {}", ty)),
+        }
     }
 }
 
 pub fn solve_constraints(
     mut constraint_db: Vec<Constraint>,
-) -> TypeInferenceResult<HashMap<ArcIntern<String>, Type>> {
-    let mut type_renames = HashMap::new();
+) -> TypeInferenceResult<TypeResolutions> {
     let mut errors = vec![];
     let mut warnings = vec![];
+    let mut resolutions = HashMap::new();
     let mut changed_something = true;
 
     // We want to run this inference endlessly, until either we have solved all of our
     // constraints. Internal to the loop, we have a check that will make sure that we
     // do (eventually) stop.
     while changed_something && !constraint_db.is_empty() {
+        println!("-------CONSTRAINTS---------");
+        for constraint in constraint_db.iter() {
+            println!("{}", constraint);
+        }
+        println!("---------------------------");
         // Set this to false at the top of the loop. We'll set this to true if we make
         // progress in any way further down, but having this here prevents us from going
         // into an infinite look when we can't figure stuff out.
@@ -115,43 +206,64 @@ pub fn solve_constraints(
                 // Currently, all of our types are printable
                 Constraint::Printable(_loc, _ty) => changed_something = true,
 
-                // If the first type is a variable, then we rename it to the second.
-                Constraint::Equivalent(_, Type::Variable(_, n), second) => {
-                    type_renames.insert(n, second);
-                    changed_something = true;
-                }
-
-                // If the second type is a variable (I guess the first wasn't, then rename it to the first)
-                Constraint::Equivalent(_, first, Type::Variable(_, n)) => {
-                    type_renames.insert(n, first);
-                    changed_something = true;
-                }
-
-                // Otherwise, we ar testing if two concrete types are equivalent, and just need to see
-                // if they're the same.
-                Constraint::Equivalent(loc, Type::Primitive(a), Type::Primitive(b)) => {
-                    if a != b {
-                        errors.push(TypeInferenceError::NotEquivalent(loc, a, b));
+                // Case #1: We have two primitive types. If they're equal, we've discharged this
+                // constraint! We can just continue. If they're not equal, add an error and then
+                // see what else we come up with.
+                Constraint::Equivalent(loc, Type::Primitive(t1), Type::Primitive(t2)) => {
+                    if t1 != t2 {
+                        errors.push(TypeInferenceError::NotEquivalent(loc, t1, t2));
                     }
                     changed_something = true;
                 }
 
+                // Case #2: One of the two constraints is a primitive, and the other is a variable.
+                // In this case, we'll check to see if we've resolved the variable, and check for
+                // equivalence if we have. If we haven't, we'll set that variable to be primitive
+                // type.
+                Constraint::Equivalent(loc, Type::Primitive(t), Type::Variable(_, name))
+                | Constraint::Equivalent(loc, Type::Variable(_, name), Type::Primitive(t)) => {
+                    match resolutions.get(&name) {
+                        None => {
+                            resolutions.insert(name, t);
+                        }
+                        Some(t2) if &t == t2 => {}
+                        Some(t2) => errors.push(TypeInferenceError::NotEquivalent(loc, t, *t2)),
+                    }
+                    changed_something = true;
+                }
+
+                // Case #3: They're both variables. In which case, we'll have to do much the same
+                // check, but now on their resolutions.
+                Constraint::Equivalent(
+                    ref loc,
+                    Type::Variable(_, ref name1),
+                    Type::Variable(_, ref name2),
+                ) => match (resolutions.get(name1), resolutions.get(name2)) {
+                    (None, None) => {
+                        constraint_db.push(constraint);
+                    }
+                    (Some(pt), None) => {
+                        resolutions.insert(name2.clone(), *pt);
+                        changed_something = true;
+                    }
+                    (None, Some(pt)) => {
+                        resolutions.insert(name1.clone(), *pt);
+                        changed_something = true;
+                    }
+                    (Some(pt1), Some(pt2)) if pt1 == pt2 => {
+                        changed_something = true;
+                    }
+                    (Some(pt1), Some(pt2)) => {
+                        errors.push(TypeInferenceError::NotEquivalent(loc.clone(), *pt1, *pt2));
+                        changed_something = true;
+                    }
+                },
+
                 // Make sure that the provided number fits within the provided constant type. For the
                 // moment, we're going to call an error here a failure, although this could be a
                 // warning in the future.
                 Constraint::FitsInNumType(loc, Type::Primitive(ctype), val) => {
-                    let is_too_big = match ctype {
-                        PrimitiveType::U8 => (u8::MAX as u64) < val,
-                        PrimitiveType::U16 => (u16::MAX as u64) < val,
-                        PrimitiveType::U32 => (u32::MAX as u64) < val,
-                        PrimitiveType::U64 => false,
-                        PrimitiveType::I8 => (i8::MAX as u64) < val,
-                        PrimitiveType::I16 => (i16::MAX as u64) < val,
-                        PrimitiveType::I32 => (i32::MAX as u64) < val,
-                        PrimitiveType::I64 => (i64::MAX as u64) < val,
-                    };
-
-                    if is_too_big {
+                    if ctype.max_value() < val {
                         errors.push(TypeInferenceError::ConstantTooLarge(loc, ctype, val));
                     }
 
@@ -161,10 +273,18 @@ pub fn solve_constraints(
                 // If we have a non-constant type, then let's see if we can advance this to a constant
                 // type
                 Constraint::FitsInNumType(loc, Type::Variable(vloc, var), val) => {
-                    match type_renames.get(&var) {
-                        None => constraint_db.push(Constraint::FitsInNumType(loc, Type::Variable(vloc, var), val)),
+                    match resolutions.get(&var) {
+                        None => constraint_db.push(Constraint::FitsInNumType(
+                            loc,
+                            Type::Variable(vloc, var),
+                            val,
+                        )),
                         Some(nt) => {
-                            constraint_db.push(Constraint::FitsInNumType(loc, nt.clone(), val));
+                            constraint_db.push(Constraint::FitsInNumType(
+                                loc,
+                                Type::Primitive(*nt),
+                                val,
+                            ));
                             changed_something = true;
                         }
                     }
@@ -173,10 +293,18 @@ pub fn solve_constraints(
                 // If the left type in a "can cast to" check is a variable, let's see if we can advance
                 // it into something more tangible
                 Constraint::CanCastTo(loc, Type::Variable(vloc, var), to_type) => {
-                    match type_renames.get(&var) {
-                        None => constraint_db.push(Constraint::CanCastTo(loc, Type::Variable(vloc, var), to_type)),
+                    match resolutions.get(&var) {
+                        None => constraint_db.push(Constraint::CanCastTo(
+                            loc,
+                            Type::Variable(vloc, var),
+                            to_type,
+                        )),
                         Some(nt) => {
-                            constraint_db.push(Constraint::CanCastTo(loc, nt.clone(), to_type));
+                            constraint_db.push(Constraint::CanCastTo(
+                                loc,
+                                Type::Primitive(*nt),
+                                to_type,
+                            ));
                             changed_something = true;
                         }
                     }
@@ -184,10 +312,18 @@ pub fn solve_constraints(
 
                 // If the right type in a "can cast to" check is a variable, same deal
                 Constraint::CanCastTo(loc, from_type, Type::Variable(vloc, var)) => {
-                    match type_renames.get(&var) {
-                        None => constraint_db.push(Constraint::CanCastTo(loc, from_type, Type::Variable(vloc, var))),
+                    match resolutions.get(&var) {
+                        None => constraint_db.push(Constraint::CanCastTo(
+                            loc,
+                            from_type,
+                            Type::Variable(vloc, var),
+                        )),
                         Some(nt) => {
-                            constraint_db.push(Constraint::CanCastTo(loc, from_type, nt.clone()));
+                            constraint_db.push(Constraint::CanCastTo(
+                                loc,
+                                from_type,
+                                Type::Primitive(*nt),
+                            ));
                             changed_something = true;
                         }
                     }
@@ -210,10 +346,11 @@ pub fn solve_constraints(
                 // As per usual, if we're trying to test if a type variable is numeric, first
                 // we try to advance it to a primitive
                 Constraint::NumericType(loc, Type::Variable(vloc, var)) => {
-                    match type_renames.get(&var) {
-                        None => constraint_db.push(Constraint::NumericType(loc, Type::Variable(vloc, var))),
+                    match resolutions.get(&var) {
+                        None => constraint_db
+                            .push(Constraint::NumericType(loc, Type::Variable(vloc, var))),
                         Some(nt) => {
-                            constraint_db.push(Constraint::NumericType(loc, nt.clone()));
+                            constraint_db.push(Constraint::NumericType(loc, Type::Primitive(*nt)));
                             changed_something = true;
                         }
                     }
@@ -254,7 +391,11 @@ pub fn solve_constraints(
                         constraint_db.push(Constraint::NumericType(loc.clone(), left.clone()));
                         constraint_db.push(Constraint::NumericType(loc.clone(), right.clone()));
                         constraint_db.push(Constraint::NumericType(loc.clone(), ret.clone()));
-                        constraint_db.push(Constraint::Equivalent(loc.clone(), left.clone(), right));
+                        constraint_db.push(Constraint::Equivalent(
+                            loc.clone(),
+                            left.clone(),
+                            right,
+                        ));
                         constraint_db.push(Constraint::Equivalent(loc, left, ret));
                         changed_something = true;
                     }
@@ -287,7 +428,11 @@ pub fn solve_constraints(
                         constraint_db.push(Constraint::NumericType(loc.clone(), left.clone()));
                         constraint_db.push(Constraint::NumericType(loc.clone(), right.clone()));
                         constraint_db.push(Constraint::NumericType(loc.clone(), ret.clone()));
-                        constraint_db.push(Constraint::Equivalent(loc.clone(), left.clone(), right));
+                        constraint_db.push(Constraint::Equivalent(
+                            loc.clone(),
+                            left.clone(),
+                            right,
+                        ));
                         constraint_db.push(Constraint::Equivalent(loc.clone(), left, ret));
                         changed_something = true;
                     }
@@ -307,9 +452,13 @@ pub fn solve_constraints(
 
             for constraint in local_constraints.drain(..) {
                 match constraint {
-                    Constraint::NumericType(loc, Type::Variable(_, name)) => {
+                    Constraint::NumericType(loc, t @ Type::Variable(_, _)) => {
                         let resty = Type::Primitive(PrimitiveType::U64);
-                        type_renames.insert(name, resty.clone());
+                        constraint_db.push(Constraint::Equivalent(
+                            loc.clone(),
+                            t,
+                            Type::Primitive(PrimitiveType::U64),
+                        ));
                         warnings.push(TypeInferenceWarning::DefaultedTo(loc, resty));
                         changed_something = true;
                     }
@@ -332,7 +481,7 @@ pub fn solve_constraints(
     // How'd we do?
     if errors.is_empty() {
         TypeInferenceResult::Success {
-            result: type_renames,
+            result: resolutions,
             warnings,
         }
     } else {

src/syntax/arbitrary.rs

@@ -10,7 +10,7 @@ use std::collections::HashMap;
 const VALID_VARIABLE_NAMES: &str = r"[a-z][a-zA-Z0-9_]*";
 const OPERATORS: &[(&str, usize)] = &[("+", 2), ("-", 1), ("-", 2), ("*", 2), ("/", 2)];
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 struct Name(String);
 
 impl Arbitrary for Name {
@@ -22,153 +22,133 @@ impl Arbitrary for Name {
     }
 }
 
+#[derive(Debug)]
+struct ProgramStatementInfo {
+    should_be_binding: bool,
+    name: Name,
+    binding_type: ConstantType,
+}
+
+impl Arbitrary for ProgramStatementInfo {
+    type Parameters = ();
+    type Strategy = BoxedStrategy<Self>;
+
+    fn arbitrary_with(_args: Self::Parameters) -> Self::Strategy {
+        (
+            Union::new(vec![Just(true), Just(true), Just(false)]),
+            Name::arbitrary(),
+            ConstantType::arbitrary(),
+        )
+            .prop_map(
+                |(should_be_binding, name, binding_type)| ProgramStatementInfo {
+                    should_be_binding,
+                    name,
+                    binding_type,
+                },
+            )
+            .boxed()
+    }
+}
+
 impl Arbitrary for Program {
     type Parameters = ();
     type Strategy = BoxedStrategy<Self>;
 
     fn arbitrary_with(_: Self::Parameters) -> Self::Strategy {
-        let optionals = Vec::<(Name, ConstantType, u8)>::arbitrary();
-
-        optionals
-            .prop_flat_map(|mut possible_names| {
+        proptest::collection::vec(ProgramStatementInfo::arbitrary(), 1..100)
+            .prop_flat_map(|mut items| {
                 let mut statements = Vec::new();
-                let mut defined_variables: HashMap<String, ConstantType> = HashMap::new();
+                let mut defined_variables = HashMap::new();
 
-                for (possible_name, possible_type, dice_roll) in possible_names.drain(..) {
-                    if !defined_variables.is_empty() && dice_roll < 100 {
+                for psi in items.drain(..) {
+                    if defined_variables.is_empty() || psi.should_be_binding {
+                        let expr = Expression::arbitrary_with(ExpressionGeneratorSettings {
+                            bound_variables: defined_variables.clone(),
+                            output_type: Some(psi.binding_type),
+                        });
+
+                        defined_variables.insert(psi.name.0.clone(), psi.binding_type);
                         statements.push(
-                            Union::new(defined_variables.keys().map(|name| {
-                                Just(Statement::Print(Location::manufactured(), name.to_string()))
-                            }))
+                            expr.prop_map(move |expr| {
+                                Statement::Binding(
+                                    Location::manufactured(),
+                                    psi.name.0.clone(),
+                                    expr,
+                                )
+                            })
                             .boxed(),
                         );
                     } else {
-                        let closures_name = possible_name.0.clone();
-                        let retval = Expression::arbitrary_with((
-                            Some(defined_variables.clone()),
-                            Some(possible_type),
-                        ))
-                        .prop_map(move |exp| {
-                            Statement::Binding(Location::manufactured(), closures_name.clone(), exp)
-                        })
-                        .boxed();
-
-                        defined_variables.insert(possible_name.0, possible_type);
-                        statements.push(retval);
+                        let printers = defined_variables
+                            .keys()
+                            .map(|n| Just(Statement::Print(Location::manufactured(), n.clone())));
+                        statements.push(Union::new(printers).boxed());
                     }
                 }
 
                 statements
+                    .prop_map(|statements| Program { statements })
+                    .boxed()
             })
-            .prop_map(|statements| Program { statements })
             .boxed()
     }
 }
 
-impl Arbitrary for Statement {
-    type Parameters = Option<HashMap<String, ConstantType>>;
-    type Strategy = BoxedStrategy<Self>;
-
-    fn arbitrary_with(args: Self::Parameters) -> Self::Strategy {
-        let duplicated_args = args.clone();
-        let defined_variables = args.unwrap_or_default();
-
-        let binding_strategy = (
-            VALID_VARIABLE_NAMES,
-            Expression::arbitrary_with((duplicated_args, None)),
-        )
-            .prop_map(|(name, exp)| Statement::Binding(Location::manufactured(), name, exp))
-            .boxed();
-
-        if defined_variables.is_empty() {
-            binding_strategy
-        } else {
-            let print_strategy = Union::new(
-                defined_variables
-                    .keys()
-                    .map(|x| Just(Statement::Print(Location::manufactured(), x.to_string()))),
-            )
-            .boxed();
-
-            Union::new([binding_strategy, print_strategy]).boxed()
-        }
-    }
+#[derive(Default)]
+pub struct ExpressionGeneratorSettings {
+    bound_variables: HashMap<String, ConstantType>,
+    output_type: Option<ConstantType>,
 }
 
 impl Arbitrary for Expression {
-    type Parameters = (Option<HashMap<String, ConstantType>>, Option<ConstantType>);
+    type Parameters = ExpressionGeneratorSettings;
     type Strategy = BoxedStrategy<Self>;
 
-    fn arbitrary_with((env, target_type): Self::Parameters) -> Self::Strategy {
-        let defined_variables = env.unwrap_or_default();
-        let mut acceptable_variables = defined_variables
-            .iter()
-            .filter(|(_, ctype)| Some(**ctype) == target_type)
-            .map(|(x, _)| x)
-            .peekable();
-
-        let value_strategy = Value::arbitrary_with(target_type)
-            .prop_map(move |x| Expression::Value(Location::manufactured(), x))
+    fn arbitrary_with(params: Self::Parameters) -> Self::Strategy {
+        // Value(Location, Value). These are the easiest variations to create, because we can always
+        // create one.
+        let value_strategy = Value::arbitrary_with(params.output_type)
+            .prop_map(|x| Expression::Value(Location::manufactured(), x))
             .boxed();
 
-        let leaf_strategy = if acceptable_variables.peek().is_none() {
+        // Reference(Location, String), These are slightly trickier, because we can end up in a situation
+        // where either no variables are defined, or where none of the defined variables have a type we
+        // can work with. So what we're going to do is combine this one with the previous one as a "leaf
+        // strategy" -- our non-recursive items -- if we can, or just set that to be the value strategy
+        // if we can't actually create an references.
+        let mut bound_variables_of_type = params
+            .bound_variables
+            .iter()
+            .filter(|(_, v)| {
+                params
+                    .output_type
+                    .as_ref()
+                    .map(|ot| ot == *v)
+                    .unwrap_or(true)
+            })
+            .map(|(n, _)| n)
+            .collect::<Vec<_>>();
+        let leaf_strategy = if bound_variables_of_type.is_empty() {
             value_strategy
         } else {
-            let reference_strategy = Union::new(acceptable_variables.map(|x| {
-                Just(Expression::Reference(
-                    Location::manufactured(),
-                    x.to_owned(),
-                ))
-            }))
-            .boxed();
-            Union::new([value_strategy, reference_strategy]).boxed()
+            let mut strats = bound_variables_of_type
+                .drain(..)
+                .map(|x| Just(Expression::Reference(Location::manufactured(), x.clone())).boxed())
+                .collect::<Vec<_>>();
+            strats.push(value_strategy);
+            Union::new(strats).boxed()
         };
 
-        let cast_strategy = if let Some(bigger_type) = target_type {
-            let mut smaller_types = bigger_type.safe_casts_to();
-
-            if smaller_types.is_empty() {
-                leaf_strategy
-            } else {
-                let duplicated_env = defined_variables.clone();
-                let cast_exp = |t, e| Expression::Cast(Location::manufactured(), t, Box::new(e));
-
-                let smaller_strats: Vec<BoxedStrategy<Expression>> = smaller_types
-                    .drain(..)
-                    .map(|t| {
-                        Expression::arbitrary_with((Some(duplicated_env.clone()), Some(t)))
-                            .prop_map(move |e| cast_exp(t.name(), e))
-                            .boxed()
-                    })
-                    .collect();
-                Union::new(smaller_strats).boxed()
-            }
-        } else {
-            leaf_strategy
-        };
-
-        cast_strategy
-            .prop_recursive(3, 64, 2, move |inner| {
-                (select(OPERATORS), proptest::collection::vec(inner, 2)).prop_map(
-                    move |((operator, arg_count), mut exprs)| {
-                        if arg_count == 1 && operator == "-" {
-                            if target_type.map(|x| x.is_signed()).unwrap_or(false) {
-                                Expression::Primitive(
-                                    Location::manufactured(),
-                                    operator.to_string(),
-                                    exprs,
-                                )
-                            } else {
-                                exprs.pop().unwrap()
-                            }
-                        } else {
-                            exprs.truncate(arg_count);
-                            Expression::Primitive(
-                                Location::manufactured(),
-                                operator.to_string(),
-                                exprs,
-                            )
+        // now we generate our recursive types, given our leaf strategy
+        leaf_strategy
+            .prop_recursive(3, 10, 2, move |strat| {
+                (select(OPERATORS), strat.clone(), strat).prop_map(
+                    |((oper, count), left, right)| {
+                        let mut args = vec![left, right];
+                        while args.len() > count {
+                            args.pop();
                         }
+                        Expression::Primitive(Location::manufactured(), oper.to_string(), args)
                     },
                 )
             })
@@ -181,7 +161,7 @@ impl Arbitrary for Value {
     type Strategy = BoxedStrategy<Self>;
 
     fn arbitrary_with(target_type: Self::Parameters) -> Self::Strategy {
-        let base_strategy = Union::new([
+        let printed_base_strategy = Union::new([
             Just(None::<u8>),
             Just(Some(2)),
             Just(Some(8)),
@@ -189,14 +169,13 @@ impl Arbitrary for Value {
             Just(Some(16)),
         ]);
 
-        let type_strategy = if target_type.is_some() {
-            Just(target_type).boxed()
-        } else {
-            proptest::option::of(ConstantType::arbitrary()).boxed()
+        let type_strategy = match target_type {
+            None => proptest::option::of(ConstantType::arbitrary()).boxed(),
+            Some(target) => proptest::option::of(Just(target)).boxed(),
         };
         let value_strategy = u64::arbitrary();
 
-        (base_strategy, type_strategy, value_strategy)
+        (printed_base_strategy, type_strategy, value_strategy)
             .prop_map(move |(base, ty, value)| {
                 let converted_value = match ty {
                     Some(ConstantType::I8) => value % (i8::MAX as u64),

src/syntax/location.rs

@@ -4,7 +4,7 @@ use codespan_reporting::diagnostic::{Diagnostic, Label};
 ///
 /// Internally, locations are very tied to the `codespan_reporting` library,
 /// and the primary use of them is to serve as anchors within that library.
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct Location {
     file_idx: usize,
     offset: usize,

src/syntax/tokens.rs

@@ -179,17 +179,50 @@ impl ConstantType {
     /// Return the set of types that can be safely casted into this type.
     pub fn safe_casts_to(self) -> Vec<ConstantType> {
         match self {
-            ConstantType::I8 => vec![],
-            ConstantType::I16 => vec![ConstantType::I8],
-            ConstantType::I32 => vec![ConstantType::I16, ConstantType::I8],
-            ConstantType::I64 => vec![ConstantType::I32, ConstantType::I16, ConstantType::I8],
-            ConstantType::U8 => vec![],
-            ConstantType::U16 => vec![ConstantType::U8],
-            ConstantType::U32 => vec![ConstantType::U16, ConstantType::U8],
-            ConstantType::U64 => vec![ConstantType::U32, ConstantType::U16, ConstantType::U8],
+            ConstantType::I8 => vec![ConstantType::I8],
+            ConstantType::I16 => vec![ConstantType::I16, ConstantType::I8, ConstantType::U8],
+            ConstantType::I32 => vec![
+                ConstantType::I32,
+                ConstantType::I16,
+                ConstantType::I8,
+                ConstantType::U16,
+                ConstantType::U8,
+            ],
+            ConstantType::I64 => vec![
+                ConstantType::I64,
+                ConstantType::I32,
+                ConstantType::I16,
+                ConstantType::I8,
+                ConstantType::U32,
+                ConstantType::U16,
+                ConstantType::U8,
+            ],
+            ConstantType::U8 => vec![ConstantType::U8],
+            ConstantType::U16 => vec![ConstantType::U16, ConstantType::U8],
+            ConstantType::U32 => vec![ConstantType::U32, ConstantType::U16, ConstantType::U8],
+            ConstantType::U64 => vec![
+                ConstantType::U64,
+                ConstantType::U32,
+                ConstantType::U16,
+                ConstantType::U8,
+            ],
         }
     }
 
+    /// Return the set of all currently-available constant types
+    pub fn all_types() -> Vec<Self> {
+        vec![
+            ConstantType::U8,
+            ConstantType::U16,
+            ConstantType::U32,
+            ConstantType::U64,
+            ConstantType::I8,
+            ConstantType::I16,
+            ConstantType::I32,
+            ConstantType::I64,
+        ]
+    }
+
     /// Return the name of the given type, as a string
     pub fn name(&self) -> String {
         match self {