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    <p>A symbol table is just a versioned map of id's to values. This is one solution, using a push and pop of scopes as the versioning mechanism -- push a scope on entry of a scope defining rule and pop on exit.</p> <pre><code>package net.certiv.metal.symbol; import java.util.ArrayList; import java.util.LinkedHashMap; import java.util.Map; import net.certiv.metal.types.ScopeType; import net.certiv.metal.util.Strings; public class Scope { public final int genId; public ScopeType type; public Scope enclosingScope; protected Map&lt;String, Symbol&gt; symbolMap = new LinkedHashMap&lt;String, Symbol&gt;(); public Scope(ScopeType type, final int genId, Scope enclosingScope) { this.type = type; this.genId = genId; this.enclosingScope = enclosingScope; } /** * Define a new variable in the current scope * This is the entry point for adding new variables */ public void define(String name, ArrayList&lt;String&gt; parameters) { String params = Strings.asString(parameters, true, "."); Symbol symbol = new Symbol(null, name + params, null); define(symbol); } /** Define a symbol in the current scope */ private void define(Symbol symbol) { symbol.setScope(this); symbolMap.put(symbol.name, symbol); } /** * Look up the symbol name in this scope and, if not found, * progressively search the enclosing scopes. * Return null if not found in any applicable scope. */ private Symbol resolve(String name) { Symbol symbol = symbolMap.get(name); if (symbol != null) return symbol; if (enclosingScope != null) return enclosingScope.resolve(name); return null; // not found } /** * Lookup a variable starting in the current scope. * This is the entry point for lookups */ public Symbol resolve(String name, ArrayList&lt;String&gt; parameters) { String params = Strings.asString(parameters, true, "."); return resolve(name + params); } /** Where to look next for symbols */ public Scope enclosingScope() { return enclosingScope; } public String toString() { return symbolMap.keySet().toString(); } } package net.certiv.metal.types; public enum ScopeType { GLOBAL, LOCAL; } package net.certiv.metal.symbol; import net.certiv.metal.converter.BaseDescriptor; import net.certiv.metal.types.ValueType; public class Symbol { protected Scope scope; // the owning scope protected BaseDescriptor descriptor; protected String name; protected ValueType type; public Symbol(BaseDescriptor descriptor, String name, ValueType type) { this.descriptor = descriptor; this.name = name; this.type = type; } public BaseDescriptor getDescriptor() { return descriptor; } public String getName() { return name; } public ValueType getType() { return type; } public void setScope(Scope scope) { this.scope = scope; } public Scope getScope() { return scope; } public int genId() { return scope.genId; } public String toString() { if (type != null) return '&lt;' + getName() + ":" + type + '&gt;'; return getName(); } } package net.certiv.metal.symbol; import java.util.ArrayList; import java.util.Stack; import net.certiv.metal.types.ScopeType; import net.certiv.metal.util.Log; public class SymbolTable { protected Stack&lt;Scope&gt; scopeStack; protected ArrayList&lt;Scope&gt; allScopes; protected int genId; public SymbolTable() { init(); } protected void init() { scopeStack = new Stack&lt;&gt;(); allScopes = new ArrayList&lt;&gt;(); genId = 0; Scope globals = new Scope(ScopeType.GLOBAL, nextGenId(), null); scopeStack.push(globals); allScopes.add(globals); } public Scope pushScope() { Scope enclosingScope = scopeStack.peek(); Scope scope = new Scope(ScopeType.LOCAL, nextGenId(), enclosingScope); scopeStack.push(scope); allScopes.add(scope); return scope; } public void popScope() { scopeStack.pop(); } public Scope currentScope() { if (scopeStack.size() &gt; 0) { return scopeStack.peek(); } Log.error(this, "Unbalanced scope stack."); return allScopes.get(0); } public Scope getScope(int genId) { for (Scope scope : scopeStack) { if (scope.genId == genId) return scope; } return null; } private int nextGenId() { genId++; return genId; } public String toString() { StringBuilder sb = new StringBuilder(); for (Scope scope : scopeStack.subList(0, scopeStack.size() - 1)) { sb.append(scope.toString()); } return sb.toString(); } } </code></pre>
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    1. COA symbol table is really a map of every identifier instance to a descriptor of the type instance for that identifier. Scopes are a way to organize how symbols in one part of the code map to known symbol declarations in the scope. This answer is right in a simple way: many older languages could be processed by a simple stack of scopes. More modern languages, with namespaces and generics, aren't nearly as simple, although the map idea remains.
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      1. USIra Baxter
    2. CONot sure if you read too quickly or what, but the answer is quite correct as presented. The code is is given as "one solution" to illustrate the mechanisms of working with a symbol table, which is in direct answer to the OP's question. Any existential qualifications can be implemented on the mapping of ids to values, but that was not an element of the OP's question. Besides, there are languages that are typeless/singly typed, which from the OP's grammar, may be the case for the OP. Namespaces and generics, both handled by forms of versioning, are not implicated in the OP's grammar.
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    3. COI wasn't complaining about your solution as a sketch (note: no ding!), just observing that building symbol tables for real langauges will likely require more than this. Maybe his language is simple. He better decide before he starts implementing, which was my original point about reading about symbol tables in detail before rushing off to do something.
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