diff --git a/schala-lang/language/src/symbol_table/mod.rs b/schala-lang/language/src/symbol_table/mod.rs
index 09a20d9..90d83a9 100644
--- a/schala-lang/language/src/symbol_table/mod.rs
+++ b/schala-lang/language/src/symbol_table/mod.rs
@@ -24,7 +24,7 @@ macro_rules! fqsn {
 }
 
 mod tables;
-use tables::SourceMap;
+use tables::DeclLocations;
 mod symbol_trie;
 use symbol_trie::SymbolTrie;
 mod test;
@@ -40,14 +40,14 @@ impl DuplicateNameTrackTable {
     DuplicateNameTrackTable { table: HashMap::new() }
   }
 
-  fn try_register(&mut self, name: &Rc<String>, id: &ItemId, source_map: &SourceMap) -> Result<(), LineNumber> {
+  fn try_register(&mut self, name: &Rc<String>, id: &ItemId, decl_locations: &DeclLocations) -> Result<(), LineNumber> {
     match self.table.entry(name.clone()) {
       Entry::Occupied(o) => {
         let line_number = o.get();
         Err(*line_number)
       },
       Entry::Vacant(v) => {
-        let line_number = if let Some(loc) = source_map.lookup(id) {
+        let line_number = if let Some(loc) = decl_locations.lookup(id) {
           loc.line_num
         } else {
           0
@@ -94,7 +94,7 @@ impl ScopeSegment {
 
 //cf. p. 150 or so of Language Implementation Patterns
 pub struct SymbolTable {
-  source_map: SourceMap,
+  decl_locations: DeclLocations,
   symbol_path_to_symbol: HashMap<FullyQualifiedSymbolName, Symbol>,
   id_to_fqsn: HashMap<ItemId, FullyQualifiedSymbolName>,
   symbol_trie: SymbolTrie,
@@ -103,7 +103,7 @@ pub struct SymbolTable {
 impl SymbolTable {
   pub fn new() -> SymbolTable {
     SymbolTable {
-      source_map: SourceMap::new(),
+      decl_locations: DeclLocations::new(),
       symbol_path_to_symbol: HashMap::new(),
       id_to_fqsn: HashMap::new(),
       symbol_trie: SymbolTrie::new()
@@ -200,16 +200,16 @@ impl SymbolTable {
     for statement in statements.iter() {
       match statement {
         Statement { kind: StatementKind::Declaration(decl), id, location, } => {
-          self.source_map.add_location(id, *location);
+          self.decl_locations.add_location(id, *location);
 
           match decl {
             FuncSig(ref signature) => {
-              seen_identifiers.try_register(&signature.name, id, &self.source_map)
+              seen_identifiers.try_register(&signature.name, id, &self.decl_locations)
                 .map_err(|line| format!("Duplicate function definition: {}. It's already defined at {}", signature.name, line))?;
               self.add_function_signature(signature, scope_name_stack)?
             }
             FuncDecl(ref signature, ref body) => {
-              seen_identifiers.try_register(&signature.name, id, &self.source_map)
+              seen_identifiers.try_register(&signature.name, id, &self.decl_locations)
                 .map_err(|line| format!("Duplicate function definition: {}. It's already defined at {}", signature.name, line))?;
               self.add_function_signature(signature, scope_name_stack)?;
               scope_name_stack.push(ScopeSegment{
@@ -220,12 +220,12 @@ impl SymbolTable {
               output?
             },
             TypeDecl { name, body, mutable } => {
-              seen_identifiers.try_register(&name.name, &id, &self.source_map)
+              seen_identifiers.try_register(&name.name, &id, &self.decl_locations)
                 .map_err(|line| format!("Duplicate type definition: {}. It's already defined at {}", name.name, line))?;
               self.add_type_decl(name, body, mutable, scope_name_stack)?
             },
             Binding { name, .. } => {
-              seen_identifiers.try_register(&name, &id, &self.source_map)
+              seen_identifiers.try_register(&name, &id, &self.decl_locations)
                 .map_err(|line| format!("Duplicate variable definition: {}. It's already defined at {}", name, line))?;
               self.add_new_symbol(name, scope_name_stack, SymbolSpec::Binding);
             }
@@ -233,8 +233,8 @@ impl SymbolTable {
           }
         },
         Statement { kind: StatementKind::Module(ModuleSpecifier { name, contents}), id, location } => {
-          self.source_map.add_location(id, *location);
-          seen_modules.try_register(name, id, &self.source_map)
+          self.decl_locations.add_location(id, *location);
+          seen_modules.try_register(name, id, &self.decl_locations)
             .map_err(|line| format!("Duplicate module definition: {}. It's already defined at {}", name, line))?;
           scope_name_stack.push(ScopeSegment { name: name.clone() });
           let output = self.add_symbols_from_scope(contents, scope_name_stack);
diff --git a/schala-lang/language/src/symbol_table/tables.rs b/schala-lang/language/src/symbol_table/tables.rs
index 7244d8b..fd25cdb 100644
--- a/schala-lang/language/src/symbol_table/tables.rs
+++ b/schala-lang/language/src/symbol_table/tables.rs
@@ -4,14 +4,15 @@ use crate::ast::ItemId;
 use crate::tokenizing::Location;
 
 
-//TODO rename this type to make its purpose clearer
-pub struct SourceMap {
+/// Maps top-level declarations to Locations in source code, to detect
+/// multiply-defined top level items.
+pub struct DeclLocations {
   map: HashMap<ItemId, Location>
 }
 
-impl SourceMap {
-  pub fn new() -> SourceMap {
-    SourceMap { map: HashMap::new() }
+impl DeclLocations {
+  pub fn new() -> Self {
+    Self { map: HashMap::new() }
   }
 
   pub(crate) fn add_location(&mut self, id: &ItemId, loc: Location) {