Remove arity from ReducedIR, symbol table

Instead look this up via the type context

schala-lang/language/src/reduced_ir/mod.rs

@@ -1,12 +1,13 @@
-use crate::ast;
+use std::{collections::HashMap, str::FromStr};
-use crate::symbol_table::{DefId, SymbolSpec, SymbolTable};
-use crate::builtin::Builtin;
 
-use std::str::FromStr;
+use crate::{
-use std::collections::HashMap;
+    ast,
+    builtin::Builtin,
+    symbol_table::{DefId, SymbolSpec, SymbolTable},
+};
 
-mod types;
 mod test;
+mod types;
 
 pub use types::*;
 
@@ -22,10 +23,7 @@ struct Reducer<'a> {
 
 impl<'a> Reducer<'a> {
     fn new(symbol_table: &'a SymbolTable) -> Self {
-        Self {
+        Self { symbol_table, functions: HashMap::new() }
-            symbol_table,
-            functions: HashMap::new(),
-        }
     }
 
     fn reduce(mut self, ast: &ast::AST) -> ReducedIR {
@@ -43,20 +41,26 @@ impl<'a> Reducer<'a> {
             match &kind {
                 ast::StatementKind::Expression(expr) => {
                     entrypoint.push(Statement::Expression(self.expression(expr)));
-                },
+                }
-                ast::StatementKind::Declaration(ast::Declaration::Binding { name: _, constant, expr, ..}) => {
+                ast::StatementKind::Declaration(ast::Declaration::Binding {
+                    name: _,
+                    constant,
+                    expr,
+                    ..
+                }) => {
                     let symbol = self.symbol_table.lookup_symbol(item_id).unwrap();
                     let def_id = symbol.def_id().unwrap();
-                    entrypoint.push(Statement::Binding { id: def_id, constant: *constant, expr: self.expression(expr) });
+                    entrypoint.push(Statement::Binding {
-                },
+                        id: def_id,
-                _ => ()
+                        constant: *constant,
+                        expr: self.expression(expr),
+                    });
+                }
+                _ => (),
             }
         }
 
-        ReducedIR {
+        ReducedIR { functions: self.functions, entrypoint }
-            functions: self.functions,
-            entrypoint,
-        }
     }
 
     fn top_level_statement(&mut self, statement: &ast::Statement) {
@@ -65,11 +69,10 @@ impl<'a> Reducer<'a> {
             ast::StatementKind::Expression(_expr) => {
                 //TODO expressions can in principle contain definitions, but I won't worry
                 //about it now
-            },
+            }
-            ast::StatementKind::Declaration(decl) => {
+            ast::StatementKind::Declaration(decl) =>
                 if let ast::Declaration::FuncDecl(_, statements) = decl {
                     self.insert_function_definition(item_id, statements);
-                }
                 },
             ast::StatementKind::Import(..) => (),
             ast::StatementKind::Module(_modspec) => {
@@ -81,32 +84,28 @@ impl<'a> Reducer<'a> {
     fn function_internal_statement(&mut self, statement: &ast::Statement) -> Option<Statement> {
         let ast::Statement { id: item_id, kind, .. } = statement;
         match kind {
-            ast::StatementKind::Expression(expr) => {
+            ast::StatementKind::Expression(expr) => Some(Statement::Expression(self.expression(expr))),
-                Some(Statement::Expression(self.expression(expr)))
-            },
             ast::StatementKind::Declaration(decl) => match decl {
                 ast::Declaration::FuncDecl(_, statements) => {
                     self.insert_function_definition(item_id, statements);
                     None
-                },
+                }
-                ast::Declaration::Binding { constant, expr, ..} => {
+                ast::Declaration::Binding { constant, expr, .. } => {
                     let symbol = self.symbol_table.lookup_symbol(item_id).unwrap();
                     let def_id = symbol.def_id().unwrap();
                     Some(Statement::Binding { id: def_id, constant: *constant, expr: self.expression(expr) })
-                },
+                }
 
-                _ => None
+                _ => None,
             },
-            _ => None
+            _ => None,
         }
     }
 
     fn insert_function_definition(&mut self, item_id: &ast::ItemId, statements: &ast::Block) {
         let symbol = self.symbol_table.lookup_symbol(item_id).unwrap();
         let def_id = symbol.def_id().unwrap();
-        let function_def = FunctionDefinition {
+        let function_def = FunctionDefinition { body: self.function_internal_block(statements) };
-            body: self.function_internal_block(statements)
-        };
         self.functions.insert(def_id, function_def);
     }
 
@@ -123,26 +122,20 @@ impl<'a> Reducer<'a> {
             Value(qualified_name) => self.value(qualified_name),
             Call { f, arguments } => Expression::Call {
                 f: Box::new(self.expression(f)),
-                args: arguments
+                args: arguments.iter().map(|arg| self.invocation_argument(arg)).collect(),
-                    .iter()
-                    .map(|arg| self.invocation_argument(arg))
-                    .collect(),
             },
             TupleLiteral(exprs) => Expression::Tuple(exprs.iter().map(|e| self.expression(e)).collect()),
-            IfExpression { discriminator, body, } => self.reduce_if_expression(discriminator.as_ref().map(|x| x.as_ref()), body),
+            IfExpression { discriminator, body } =>
-            Lambda { params, body, .. } =>  {
+                self.reduce_if_expression(discriminator.as_ref().map(|x| x.as_ref()), body),
-                Expression::Callable(Callable::Lambda {
+            Lambda { params, body, .. } => Expression::Callable(Callable::Lambda {
                 arity: params.len() as u8,
                 body: self.function_internal_block(body),
-                })
+            }),
-            },
             NamedStruct { name, fields } => {
                 let symbol = self.symbol_table.lookup_symbol(&name.id).unwrap();
                 let constructor = match symbol.spec() {
-                    SymbolSpec::RecordConstructor { tag, members: _, type_id } => Expression::Callable(Callable::RecordConstructor {
+                    SymbolSpec::RecordConstructor { tag, members: _, type_id } =>
-                        type_id,
+                        Expression::Callable(Callable::RecordConstructor { type_id, tag }),
-                        tag,
-                    }),
                     e => return Expression::ReductionError(format!("Bad symbol for NamedStruct: {:?}", e)),
                 };
 
@@ -153,11 +146,8 @@ impl<'a> Reducer<'a> {
                     unimplemented!()
                 }
 
-                Expression::Call {
+                Expression::Call { f: Box::new(constructor), args: ordered_args }
-                    f: Box::new(constructor),
-                    args: ordered_args,
             }
-            },
             Index { .. } => Expression::ReductionError("Index expr not implemented".to_string()),
             WhileExpression { .. } => Expression::ReductionError("While expr not implemented".to_string()),
             ForExpression { .. } => Expression::ReductionError("For expr not implemented".to_string()),
@@ -165,7 +155,11 @@ impl<'a> Reducer<'a> {
         }
     }
 
-    fn reduce_if_expression(&mut self, discriminator: Option<&ast::Expression>, body: &ast::IfExpressionBody) -> Expression {
+    fn reduce_if_expression(
+        &mut self,
+        discriminator: Option<&ast::Expression>,
+        body: &ast::IfExpressionBody,
+    ) -> Expression {
         use ast::IfExpressionBody::*;
 
         let cond = Box::new(match discriminator {
@@ -173,26 +167,15 @@ impl<'a> Reducer<'a> {
             None => return Expression::ReductionError("blank cond if-expr not supported".to_string()),
         });
         match body {
-            SimpleConditional {
+            SimpleConditional { then_case, else_case } => {
-                then_case,
-                else_case,
-            } => {
                 let then_clause = self.function_internal_block(then_case);
                 let else_clause = match else_case.as_ref() {
                     None => vec![],
                     Some(stmts) => self.function_internal_block(stmts),
                 };
-                Expression::Conditional {
+                Expression::Conditional { cond, then_clause, else_clause }
-                    cond,
-                    then_clause,
-                    else_clause,
             }
-            },
+            SimplePatternMatch { pattern, then_case, else_case } => {
-            SimplePatternMatch {
-                pattern,
-                then_case,
-                else_case,
-            } => {
                 let alternatives = vec![
                     Alternative {
                         pattern: match pattern.reduce(self.symbol_table) {
@@ -211,24 +194,28 @@ impl<'a> Reducer<'a> {
                 ];
 
                 Expression::CaseMatch { cond, alternatives }
-            },
+            }
             CondList(ref condition_arms) => {
                 let mut alternatives = vec![];
                 for arm in condition_arms {
                     match arm.condition {
-                        ast::Condition::Expression(ref _expr) => return Expression::ReductionError("case-expression".to_string()),
+                        ast::Condition::Expression(ref _expr) =>
+                            return Expression::ReductionError("case-expression".to_string()),
                         ast::Condition::Pattern(ref pat) => {
                             let alt = Alternative {
                                 pattern: match pat.reduce(self.symbol_table) {
                                     Ok(p) => p,
-                                    Err(e) => return Expression::ReductionError(format!("Bad pattern: {:?}", e)),
+                                    Err(e) =>
+                                        return Expression::ReductionError(format!("Bad pattern: {:?}", e)),
                                 },
                                 item: self.function_internal_block(&arm.body),
                             };
                             alternatives.push(alt);
-                        },
+                        }
-                        ast::Condition::TruncatedOp(_, _) =>  return Expression::ReductionError("case-expression-trunc-op".to_string()),
+                        ast::Condition::TruncatedOp(_, _) =>
-                        ast::Condition::Else => return Expression::ReductionError("case-expression-else".to_string()),
+                            return Expression::ReductionError("case-expression-trunc-op".to_string()),
+                        ast::Condition::Else =>
+                            return Expression::ReductionError("case-expression-else".to_string()),
                     }
                 }
                 Expression::CaseMatch { cond, alternatives }
@@ -252,12 +239,10 @@ impl<'a> Reducer<'a> {
     fn prefix(&mut self, prefix: &ast::PrefixOp, arg: &ast::Expression) -> Expression {
         let builtin: Option<Builtin> = TryFrom::try_from(prefix).ok();
         match builtin {
-            Some(op) => {
+            Some(op) => Expression::Call {
-                Expression::Call {
                 f: Box::new(Expression::Callable(Callable::Builtin(op))),
                 args: vec![self.expression(arg)],
-                }
+            },
-            }
             None => {
                 //TODO need this for custom prefix ops
                 Expression::ReductionError("User-defined prefix ops not supported".to_string())
@@ -278,21 +263,18 @@ impl<'a> Reducer<'a> {
                         } else {
                             return ReductionError(format!("Couldn't look up name: {:?}", qualified_name));
                         }
-                    },
+                    }
                     _ => return ReductionError("Trying to assign to a non-name".to_string()),
                 };
 
-                Expression::Assign {
+                Expression::Assign { lval, rval: Box::new(self.expression(rhs)) }
-                    lval,
-                    rval: Box::new(self.expression(rhs)),
             }
-            },
             Some(op) => Expression::Call {
                 f: Box::new(Expression::Callable(Callable::Builtin(op))),
                 args: vec![self.expression(lhs), self.expression(rhs)],
             },
             //TODO handle a user-defined operation
-            None => ReductionError("User-defined operations not supported".to_string())
+            None => ReductionError("User-defined operations not supported".to_string()),
         }
     }
 
@@ -301,7 +283,8 @@ impl<'a> Reducer<'a> {
 
         let symbol = match self.symbol_table.lookup_symbol(&qualified_name.id) {
             Some(s) => s,
-            None => return Expression::ReductionError(format!("No symbol found for name: {:?}", qualified_name))
+            None =>
+                return Expression::ReductionError(format!("No symbol found for name: {:?}", qualified_name)),
         };
 
         let def_id = symbol.def_id();
@@ -311,14 +294,12 @@ impl<'a> Reducer<'a> {
             GlobalBinding => Expression::Lookup(Lookup::GlobalVar(def_id.unwrap())),
             LocalVariable => Expression::Lookup(Lookup::LocalVar(def_id.unwrap())),
             FunctionParam(n) => Expression::Lookup(Lookup::Param(n)),
-            DataConstructor { tag, arity, type_id } => Expression::Callable(Callable::DataConstructor {
+            DataConstructor { tag, type_id } =>
-                type_id,
+                Expression::Callable(Callable::DataConstructor { type_id, tag }),
-                arity: arity as u32,
+            RecordConstructor { .. } => Expression::ReductionError(format!(
-                tag,
+                "The symbol for value {:?} is unexpectdly a RecordConstructor",
-            }),
+                qualified_name
-            RecordConstructor { .. } => {
+            )),
-                Expression::ReductionError(format!("The symbol for value {:?} is unexpectdly a RecordConstructor", qualified_name))
-            },
         }
     }
 }
@@ -328,60 +309,53 @@ impl ast::Pattern {
         Ok(match self {
             ast::Pattern::Ignored => Pattern::Ignored,
             ast::Pattern::TuplePattern(subpatterns) => {
-                let items: Result<Vec<Pattern>, PatternError> = subpatterns.iter()
+                let items: Result<Vec<Pattern>, PatternError> =
-                    .map(|pat| pat.reduce(symbol_table)).into_iter().collect();
+                    subpatterns.iter().map(|pat| pat.reduce(symbol_table)).into_iter().collect();
                 let items = items?;
-                Pattern::Tuple {
+                Pattern::Tuple { tag: None, subpatterns: items }
-                    tag: None,
-                    subpatterns: items,
             }
-            },
             ast::Pattern::Literal(lit) => Pattern::Literal(match lit {
                 ast::PatternLiteral::NumPattern { neg, num } => match (neg, num) {
                     (false, ast::ExpressionKind::NatLiteral(n)) => Literal::Nat(*n),
                     (false, ast::ExpressionKind::FloatLiteral(f)) => Literal::Float(*f),
                     (true, ast::ExpressionKind::NatLiteral(n)) => Literal::Int(-(*n as i64)),
                     (true, ast::ExpressionKind::FloatLiteral(f)) => Literal::Float(-f),
-                    (_, e) => return Err(format!("Internal error, unexpected pattern literal: {:?}", e).into())
+                    (_, e) =>
+                        return Err(format!("Internal error, unexpected pattern literal: {:?}", e).into()),
                 },
                 ast::PatternLiteral::StringPattern(s) => Literal::StringLit(s.clone()),
                 ast::PatternLiteral::BoolPattern(b) => Literal::Bool(*b),
             }),
             ast::Pattern::TupleStruct(name, subpatterns) => {
                 let symbol = symbol_table.lookup_symbol(&name.id).unwrap();
-                if let SymbolSpec::DataConstructor { tag, type_id: _, arity: _ } = symbol.spec() {
+                if let SymbolSpec::DataConstructor { tag, type_id: _ } = symbol.spec() {
-                    let items: Result<Vec<Pattern>, PatternError> = subpatterns.iter().map(|pat| pat.reduce(symbol_table))
+                    let items: Result<Vec<Pattern>, PatternError> =
-                        .into_iter().collect();
+                        subpatterns.iter().map(|pat| pat.reduce(symbol_table)).into_iter().collect();
                     let items = items?;
-                    Pattern::Tuple {
+                    Pattern::Tuple { tag: Some(tag), subpatterns: items }
-                        tag: Some(tag),
-                        subpatterns: items,
-                    }
                 } else {
-                    return Err("Internal error, trying to match something that's not a DataConstructor".into());
+                    return Err(
+                        "Internal error, trying to match something that's not a DataConstructor".into()
+                    );
+                }
             }
-            },
             ast::Pattern::VarOrName(name) => {
                 let symbol = symbol_table.lookup_symbol(&name.id).unwrap();
                 match symbol.spec() {
-                    SymbolSpec::DataConstructor { tag, type_id: _, arity: _ } => {
+                    SymbolSpec::DataConstructor { tag, type_id: _ } =>
-                        Pattern::Tuple {
+                        Pattern::Tuple { tag: Some(tag), subpatterns: vec![] },
-                            tag: Some(tag),
-                            subpatterns: vec![]
-                        }
-                    },
                     SymbolSpec::LocalVariable => {
                         let def_id = symbol.def_id().unwrap();
                         Pattern::Binding(def_id)
-                    },
-                    spec => return Err(format!("Unexpected VarOrName symbol: {:?}", spec).into())
                     }
-            },
+                    spec => return Err(format!("Unexpected VarOrName symbol: {:?}", spec).into()),
-            ast::Pattern::Record(name, _specified_members/*Vec<(Rc<String>, Pattern)>*/) => {
+                }
+            }
+            ast::Pattern::Record(name, _specified_members /*Vec<(Rc<String>, Pattern)>*/) => {
                 let symbol = symbol_table.lookup_symbol(&name.id).unwrap();
                 match symbol.spec() {
                     SymbolSpec::RecordConstructor { tag: _, members: _, type_id: _ } => unimplemented!(),
-                    spec => return Err(format!("Unexpected Record pattern symbol: {:?}", spec).into())
+                    spec => return Err(format!("Unexpected Record pattern symbol: {:?}", spec).into()),
                 }
             }
         })

schala-lang/language/src/reduced_ir/types.rs

@@ -1,10 +1,10 @@
-use std::collections::HashMap;
+use std::{collections::HashMap, convert::From, rc::Rc};
-use std::rc::Rc;
-use std::convert::From;
 
-use crate::builtin::Builtin;
+use crate::{
-use crate::symbol_table::{DefId, SymbolTable};
+    builtin::Builtin,
-use crate::type_inference::TypeId;
+    symbol_table::{DefId, SymbolTable},
+    type_inference::TypeId,
+};
 
 //TODO most of these Clone impls only exist to support function application, because the
 //tree-walking evaluator moves the reduced IR members.
@@ -41,11 +41,7 @@ impl ReducedIR {
 #[derive(Debug, Clone)]
 pub enum Statement {
     Expression(Expression),
-    Binding {
+    Binding { id: DefId, constant: bool, expr: Expression },
-        id: DefId,
-        constant: bool,
-        expr: Expression
-    },
 }
 
 #[derive(Debug, Clone)]
@@ -53,24 +49,11 @@ pub enum Expression {
     Literal(Literal),
     Tuple(Vec<Expression>),
     Lookup(Lookup),
-    Assign {
+    Assign { lval: DefId, rval: Box<Expression> },
-        lval: DefId,
-        rval: Box<Expression>,
-    },
     Callable(Callable),
-    Call {
+    Call { f: Box<Expression>, args: Vec<Expression> },
-        f: Box<Expression>,
+    Conditional { cond: Box<Expression>, then_clause: Vec<Statement>, else_clause: Vec<Statement> },
-        args: Vec<Expression>
+    CaseMatch { cond: Box<Expression>, alternatives: Vec<Alternative> },
-    },
-    Conditional {
-        cond: Box<Expression>,
-        then_clause: Vec<Statement>,
-        else_clause: Vec<Statement>,
-    },
-    CaseMatch {
-        cond: Box<Expression>,
-        alternatives: Vec<Alternative>,
-    },
     ReductionError(String),
 }
 
@@ -82,26 +65,16 @@ impl Expression {
 
 #[derive(Debug)]
 pub struct FunctionDefinition {
-    pub body: Vec<Statement>
+    pub body: Vec<Statement>,
 }
 
 #[derive(Debug, Clone)]
 pub enum Callable {
     Builtin(Builtin),
     UserDefined(DefId),
-    Lambda {
+    Lambda { arity: u8, body: Vec<Statement> },
-        arity: u8,
+    DataConstructor { type_id: TypeId, tag: u32 },
-        body: Vec<Statement>
+    RecordConstructor { type_id: TypeId, tag: u32 },
-    },
-    DataConstructor {
-        type_id: TypeId,
-        arity: u32,
-        tag: u32
-    },
-    RecordConstructor {
-        type_id: TypeId,
-        tag: u32,
-    },
 }
 
 #[derive(Debug, Clone)]
@@ -129,13 +102,10 @@ pub struct Alternative {
 
 #[derive(Debug, Clone)]
 pub enum Pattern {
-    Tuple {
+    Tuple { subpatterns: Vec<Pattern>, tag: Option<u32> },
-        subpatterns: Vec<Pattern>,
-        tag: Option<u32>,
-    },
     Literal(Literal),
     Ignored,
-    Binding(DefId)
+    Binding(DefId),
 }
 
 #[allow(dead_code)]

schala-lang/language/src/symbol_table/mod.rs

@@ -257,9 +257,7 @@ impl fmt::Display for Symbol {
 #[derive(Debug, Clone)]
 pub enum SymbolSpec {
     Func,
-    // The tag and arity here are *surface* tags, computed from the order in which they were
+    DataConstructor { tag: u32, type_id: TypeId },
-    // defined. The type context may create a different ordering.
-    DataConstructor { tag: u32, arity: usize, type_id: TypeId },
     RecordConstructor { tag: u32, members: HashMap<Rc<String>, TypeId>, type_id: TypeId },
     GlobalBinding, //Only for global variables, not for function-local ones or ones within a `let` scope context
     LocalVariable,
@@ -271,8 +269,7 @@ impl fmt::Display for SymbolSpec {
         use self::SymbolSpec::*;
         match self {
             Func => write!(f, "Func"),
-            DataConstructor { tag, type_id, arity } =>
+            DataConstructor { tag, type_id } => write!(f, "DataConstructor(tag: {}, type: {})", tag, type_id),
-                write!(f, "DataConstructor(tag: {}, arity: {}, type: {})", tag, arity, type_id),
             RecordConstructor { type_id, tag, .. } =>
                 write!(f, "RecordConstructor(tag: {})(<members> -> {})", tag, type_id),
             GlobalBinding => write!(f, "GlobalBinding"),
@@ -484,10 +481,8 @@ impl<'a> SymbolTableRunner<'a> {
             let id = fqsn_id_map.get(&fqsn).unwrap();
             let tag = index as u32;
             let spec = match &variant.members {
-                type_inference::VariantMembers::Unit =>
+                type_inference::VariantMembers::Unit => SymbolSpec::DataConstructor { tag, type_id },
-                    SymbolSpec::DataConstructor { tag, arity: 0, type_id },
+                type_inference::VariantMembers::Tuple(..) => SymbolSpec::DataConstructor { tag, type_id },
-                type_inference::VariantMembers::Tuple(items) =>
-                    SymbolSpec::DataConstructor { tag, arity: items.len(), type_id },
                 type_inference::VariantMembers::Record(..) =>
                     SymbolSpec::RecordConstructor { tag, members: HashMap::new(), type_id },
             };

schala-lang/language/src/tree_walk_eval/evaluator.rs

@@ -106,8 +106,14 @@ impl<'a, 'b> Evaluator<'a, 'b> {
                 Primitive::unit()
             }
             Expression::Call { box f, args } => self.call_expression(f, args)?,
-            Expression::Callable(Callable::DataConstructor { type_id, arity, tag }) if arity == 0 =>
+            Expression::Callable(Callable::DataConstructor { type_id, tag }) => {
-                Primitive::Object { type_id, tag, items: vec![] },
+                let arity = self.type_context.lookup_variant_arity(&type_id, tag).unwrap();
+                if arity == 0 {
+                    Primitive::Object { type_id, tag, items: vec![] }
+                } else {
+                    Primitive::Callable(Callable::DataConstructor { type_id, tag })
+                }
+            }
             Expression::Callable(func) => Primitive::Callable(func),
             Expression::Conditional { box cond, then_clause, else_clause } => {
                 let cond = self.expression(cond)?;
@@ -205,7 +211,8 @@ impl<'a, 'b> Evaluator<'a, 'b> {
                 }
                 self.apply_function(body, args)
             }
-            Callable::DataConstructor { type_id, arity, tag } => {
+            Callable::DataConstructor { type_id, tag } => {
+                let arity = self.type_context.lookup_variant_arity(&type_id, tag).unwrap();
                 if arity as usize != args.len() {
                     return Err(format!(
                         "Constructor expression requries {} arguments, only {} provided",

schala-lang/language/src/type_inference/mod.rs

@@ -31,9 +31,7 @@ impl TypeContext {
             let record_variant = matches!(members.get(0).unwrap(), VariantMemberBuilder::KeyVal(..));
 
             if record_variant {
-                let pending_members = members
+                let pending_members = members.into_iter().map(|var| match var {
-                    .into_iter()
-                    .map(|var| match var {
                     VariantMemberBuilder::KeyVal(name, ty) => (name, ty),
                     _ => panic!("Compiler internal error: variant mismatch"),
                 });
@@ -46,9 +44,7 @@ impl TypeContext {
                 pending_variants
                     .push(Variant { name: variant_builder.name, members: VariantMembers::Record(type_ids) });
             } else {
-                let pending_members = members
+                let pending_members = members.into_iter().map(|var| match var {
-                    .into_iter()
-                    .map(|var| match var {
                     VariantMemberBuilder::Pending(pending_type) => pending_type,
                     _ => panic!("Compiler internal error: variant mismatch"),
                 });
@@ -78,6 +74,16 @@ impl TypeContext {
             .map(|variant| variant.name.as_ref())
     }
 
+    pub fn lookup_variant_arity(&self, type_id: &TypeId, tag: u32) -> Option<u32> {
+        self.defined_types.get(type_id).and_then(|defined| defined.variants.get(tag as usize)).map(
+            |variant| match &variant.members {
+                VariantMembers::Unit => 0,
+                VariantMembers::Tuple(items) => items.len() as u32,
+                VariantMembers::Record(items) => items.len() as u32,
+            },
+        )
+    }
+
     pub fn lookup_type(&self, type_id: &TypeId) -> Option<&DefinedType> {
         self.defined_types.get(type_id)
     }