add interpreter

1 files changed, 49 insertions, 0 deletions

diff --git a/src/interpreter/SymbolTable.ts b/src/interpreter/SymbolTable.ts
new file mode 100644
index 0000000..e2ff7e1
--- /dev/null
+++ b/src/interpreter/SymbolTable.ts
@@ -0,0 +1,49 @@
+export class UndefinedSymbolError extends Error {}
+
+export class SymbolTable {
+  private knownSymbols: Set<string>;
+  private parent: SymbolTable | null;
+  private depth: number;
+
+  constructor(parent: SymbolTable | null = null) {
+    this.knownSymbols = new Set();
+    this.parent = parent;
+    this.depth = parent ? parent.getDepth() + 1 : 0;
+  }
+
+  public getDepth() {
+    return this.depth;
+  }
+
+  public add(name: string) {
+    this.knownSymbols.add(name);
+  }
+
+  public get(name: string): number {
+    if (this.knownSymbols.has(name)) {
+      return 1;
+    }
+
+    if (this.parent) {
+      return 1 + this.parent.get(name);
+    }
+
+    throw new UndefinedSymbolError(`Undefined variable: ${name}`);
+  }
+
+  public has(name: string): boolean {
+    if (this.knownSymbols.has(name)) {
+      return true;
+    }
+
+    if (this.parent) {
+      return this.parent.has(name);
+    }
+
+    return false;
+  }
+
+  public createChild(): SymbolTable {
+    return new SymbolTable(this);
+  }
+}