diff --git a/src/analysis.ts b/src/analysis.ts
new file mode 100644
index 000000000..df247d0d8
--- /dev/null
+++ b/src/analysis.ts
@@ -0,0 +1,192 @@
+import { DirectedHashGraph, strongconnect } from "yagl";
+import { assert } from "./util";
+import { Syntax, LetDeclaration, Scope, SourceFile, SyntaxKind } from "./cst";
+
+type NodeWithBlock
+  = LetDeclaration
+  | SourceFile
+
+export class Analyser {
+
+  private referenceGraph = new DirectedHashGraph<NodeWithBlock>();
+
+  public addSourceFile(node: SourceFile): void {
+
+    const visit = (node: Syntax, source: NodeWithBlock) => {
+
+      const addReference = (scope: Scope, name: string) => {
+        const target = scope.lookup(name);
+        if (target === null || target.kind === SyntaxKind.Param) {
+          return;
+        }
+        assert(target.kind === SyntaxKind.LetDeclaration || target.kind === SyntaxKind.SourceFile);
+        this.referenceGraph.addEdge(source, target);
+      }
+
+      switch (node.kind) {
+
+        case SyntaxKind.ConstantExpression:
+          break;
+
+        case SyntaxKind.SourceFile:
+        {
+          for (const element of node.elements) {
+            visit(element, source);
+          }
+          break;
+        }
+
+        case SyntaxKind.ReferenceExpression:
+        {
+          if (node.name.kind === SyntaxKind.Identifier) {
+            assert(node.modulePath.length === 0);
+            addReference(node.getScope(), node.name.text);
+          }
+          break;
+        }
+
+        case SyntaxKind.MemberExpression:
+        {
+          visit(node.expression, source);
+          break;
+        }
+
+        case SyntaxKind.NamedTupleExpression:
+        {
+          for (const arg of node.elements) {
+            visit(arg, source);
+          }
+          break;
+        }
+
+        case SyntaxKind.StructExpression:
+        {
+          for (const member of node.members) {
+            switch (member.kind) {
+              case SyntaxKind.PunnedStructExpressionField:
+              {
+                addReference(node.getScope(), member.name.text);
+                break;
+              }
+              case SyntaxKind.StructExpressionField:
+              {
+                visit(member.expression, source);
+                break;
+              };
+            }
+          }
+          break;
+        }
+
+        case SyntaxKind.NestedExpression:
+        {
+          visit(node.expression, source);
+          break;
+        }
+
+        case SyntaxKind.InfixExpression:
+        {
+          visit(node.left, source);
+          visit(node.right, source);
+          break;
+        }
+
+        case SyntaxKind.CallExpression:
+        {
+          visit(node.func, source);
+          for (const arg of node.args) {
+            visit(arg, source);
+          }
+          break;
+        }
+
+        case SyntaxKind.IfStatement:
+        {
+          for (const cs of node.cases) {
+            if (cs.test !== null) {
+              visit(cs.test, source);
+            }
+            for (const element of cs.elements) {
+              visit(element, source);
+            }
+          }
+          break;
+        }
+
+        case SyntaxKind.ExpressionStatement:
+        {
+          visit(node.expression, source);
+          break;
+        }
+
+        case SyntaxKind.ReturnStatement:
+        {
+          if (node.expression !== null) {
+            visit(node.expression, source);
+          }
+          break;
+        }
+
+        case SyntaxKind.LetDeclaration:
+        {
+          this.referenceGraph.addVertex(node);
+          if (node.body !== null) {
+            switch (node.body.kind) {
+              case SyntaxKind.ExprBody:
+              {
+                visit(node.body.expression, node);
+                break;
+              }
+              case SyntaxKind.BlockBody:
+              {
+                for (const element of node.body.elements) {
+                  visit(element, node);
+                }
+                break;
+              }
+            }
+          }
+          break;
+        }
+
+        case SyntaxKind.TypeDeclaration:
+        case SyntaxKind.EnumDeclaration:
+        case SyntaxKind.StructDeclaration:
+          break;
+
+        default:
+          throw new Error(`Unexpected ${node.constructor.name}`);
+
+      }
+
+    }
+
+    visit(node, node);
+
+  }
+
+  public isReferencedInParentScope(node: LetDeclaration): boolean {
+    const maxDepth = node.getScope().depth;
+    for (const other of this.referenceGraph.getSourceVertices(node)) {
+      if (other.getScope().depth < maxDepth) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Gets a sorted list of collections where each collection contains
+   * let-declarations that reference each other in some way or another.
+   *
+   * The declarations are sorted in such a way that declarations that reference
+   * nothing come before declarations that reference another declaration. When
+   * a let-declaration is not recusive, it will simply show up as a collection
+   * with only one element.
+   */
+  public getSortedDeclarations(): Iterable<NodeWithBlock[]> {
+    return strongconnect(this.referenceGraph);
+  }
+
+}
+