feature(semantic): implement chaining symbols tables in different sco…

…pe levels
ghaiklor · Jul 14, 2017 · 4791ce1 · 4791ce1
1 parent 676abea
commit 4791ce1
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Showing 4 changed files with 26 additions and 12 deletions.
diff --git a/src/semantic/SemanticAnalyzer.js b/src/semantic/SemanticAnalyzer.js
@@ -37,8 +37,9 @@ class SemanticAnalyzer {
    * @param {Program} node
    */
   onProgram(node) {
-    this.scope = SymbolTable.create('global', 1);
+    this.scope = SymbolTable.create('global', 1, this.scope);
     this.visit(node.getBlock());
+    this.scope = this.scope.enclosingScope;
   }
 
   /**
@@ -51,8 +52,7 @@ class SemanticAnalyzer {
     const procedureSymbol = ProcedureSymbol.create(procedureName);
 
     this.scope.define(procedureSymbol);
-
-    this.scope = SymbolTable.create(procedureName, 2);
+    this.scope = SymbolTable.create(procedureName, this.scope.scopeLevel + 1, this.scope);
 
     node.getParams().forEach(param => {
       const paramType = this.scope.lookup(param.getType().getValue());
@@ -64,6 +64,7 @@ class SemanticAnalyzer {
     });
 
     this.visit(node.getBlock());
+    this.scope = this.scope.enclosingScope;
   }
 
   /**
@@ -96,7 +97,7 @@ class SemanticAnalyzer {
     const varName = node.getVariable().getName();
     const varSymbol = VariableSymbol.create(varName, typeSymbol);
 
-    if (this.scope.lookup(varName)) throw new Error(`Duplicate declaration of ${varName}`);
+    if (this.scope.lookup(varName, true)) throw new Error(`Duplicate declaration of ${varName}`);
 
     this.scope.define(varSymbol);
   }

diff --git a/src/symbols/SymbolTable.js b/src/symbols/SymbolTable.js
@@ -13,16 +13,18 @@ class SymbolTable {
    *
    * @param {String} scopeName
    * @param {Number} scopeLevel
+   * @param {SymbolTable} [enclosingScope=null]
    * @example
    * const table = SymbolTable.create();
    * const symbol = VariableSymbol.create();
    *
    * table.define(symbol);
    */
-  constructor(scopeName, scopeLevel) {
+  constructor(scopeName, scopeLevel, enclosingScope = null) {
     this.symbols = new Map();
     this.scopeName = scopeName;
     this.scopeLevel = scopeLevel;
+    this.enclosingScope = enclosingScope;
 
     this.initBuiltin();
   }
@@ -55,10 +57,15 @@ class SymbolTable {
    * Lookup for a symbol in symbol table by its name.
    *
    * @param {String} name
+   * @param {Boolean} [currentScopeOnly=false]
    * @returns {Symbol}
    */
-  lookup(name) {
-    return this.symbols.get(name);
+  lookup(name, currentScopeOnly = false) {
+    const symbol = this.symbols.get(name);
+
+    if (symbol) return symbol;
+    if (currentScopeOnly) return null;
+    if (this.enclosingScope) return this.enclosingScope.lookup(name);
   }
 
   /**
@@ -82,10 +89,11 @@ class SymbolTable {
    * @static
    * @param {String} scopeName
    * @param {Number} scopeLevel
+   * @param {SymbolTable} [enclosingScope=null]
    * @returns {SymbolTable}
    */
-  static create(scopeName, scopeLevel) {
-    return new this(scopeName, scopeLevel);
+  static create(scopeName, scopeLevel, enclosingScope) {
+    return new this(scopeName, scopeLevel, enclosingScope);
   }
 }
 

diff --git a/test/semantic/SemanticAnalyzer.test.js b/test/semantic/SemanticAnalyzer.test.js
@@ -32,7 +32,7 @@ describe('Semantic::SemanticAnalyzer', () => {
     assert.throws(() => analyzer.visit(ast), Error, 'Duplicate declaration of x');
   });
 
-  it('Should properly create two symbol tables', () => {
+  it('Should properly traverse an AST and create/remove symbol tables', () => {
     const program = `
       PROGRAM main;
         VAR x, y: REAL;
@@ -41,6 +41,11 @@ describe('Semantic::SemanticAnalyzer', () => {
           VAR y: INTEGER;
         BEGIN
         END;
+        
+        PROCEDURE Beta(a: INTEGER);
+          VAR y: REAL;
+        BEGIN
+        END;
       
       BEGIN
       END.
@@ -51,7 +56,6 @@ describe('Semantic::SemanticAnalyzer', () => {
 
     analyzer.visit(ast);
 
-    assert.equal(analyzer.scope.scopeLevel, 2);
-    assert.equal(analyzer.scope.scopeName, 'Alpha');
+    assert.isNull(analyzer.scope);
   });
 });
diff --git a/test/symbols/SymbolTable.test.js b/test/symbols/SymbolTable.test.js
@@ -14,6 +14,7 @@ describe('Symbols::SymbolTable', () => {
     assert.instanceOf(table.symbols.get('REAL'), TypeSymbol);
     assert.equal(table.scopeName, 'global');
     assert.equal(table.scopeLevel, 1);
+    assert.isNull(table.enclosingScope);
   });
 
   it('Should properly define a symbol', () => {