From 219397339cf933e1a73e13c41c1bfaf6def06dcb Mon Sep 17 00:00:00 2001
From: Corey Johnson <probablycorey@gmail.com>
Date: Thu, 16 Oct 2025 17:47:01 -0700
Subject: [PATCH] feat(parser): add scope tracking context tracker
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🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 src/parser/scopeTracker.ts | 120 +++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 src/parser/scopeTracker.ts

diff --git a/src/parser/scopeTracker.ts b/src/parser/scopeTracker.ts
new file mode 100644
index 0000000..fd44057
--- /dev/null
+++ b/src/parser/scopeTracker.ts
@@ -0,0 +1,120 @@
+import { ContextTracker } from '@lezer/lr'
+import * as terms from './shrimp.terms'
+
+export class Scope {
+  constructor(
+    public parent: Scope | null,
+    public vars: Set<string>
+  ) {}
+
+  has(name: string): boolean {
+    return this.vars.has(name) || (this.parent?.has(name) ?? false)
+  }
+
+  add(name: string): Scope {
+    const newVars = new Set(this.vars)
+    newVars.add(name)
+    return new Scope(this.parent, newVars)
+  }
+
+  addAll(names: string[]): Scope {
+    const newVars = new Set(this.vars)
+    names.forEach(name => newVars.add(name))
+    return new Scope(this.parent, newVars)
+  }
+
+  push(): Scope {
+    return new Scope(this, new Set())
+  }
+
+  pop(): Scope {
+    return this.parent ?? new Scope(null, new Set())
+  }
+
+  hash(): number {
+    let h = 0
+    for (const name of this.vars) {
+      for (let i = 0; i < name.length; i++) {
+        h = (h << 5) - h + name.charCodeAt(i)
+        h |= 0
+      }
+    }
+    if (this.parent) {
+      h = (h << 5) - h + this.parent.hash()
+      h |= 0
+    }
+    return h
+  }
+}
+
+// Module-level state for tracking identifiers
+let pendingIdentifiers: string[] = []
+let isInParams = false
+
+// Term ID for 'fn' keyword - verified by parsing and inspecting the tree
+const FN_KEYWORD = 32
+
+export const trackScope = new ContextTracker<Scope>({
+  start: new Scope(null, new Set()),
+
+  shift(context, term, stack, input) {
+    // Track fn keyword to enter param capture mode
+    if (term === FN_KEYWORD) {
+      isInParams = true
+      pendingIdentifiers = []
+      return context
+    }
+
+    // Capture identifiers
+    if (term === terms.Identifier) {
+      const text = input.read(input.pos, stack.pos)
+
+      // Capture ALL identifiers when in params
+      if (isInParams) {
+        pendingIdentifiers.push(text)
+      }
+      // Capture FIRST identifier for assignments
+      else if (pendingIdentifiers.length === 0) {
+        pendingIdentifiers.push(text)
+      }
+    }
+
+    return context
+  },
+
+  reduce(context, term, stack, input) {
+    // Add assignment variable to scope
+    if (term === terms.Assign && pendingIdentifiers.length > 0) {
+      const newContext = context.add(pendingIdentifiers[0])
+      pendingIdentifiers = []
+      return newContext
+    }
+
+    // Push new scope and add parameters
+    if (term === terms.Params) {
+      const newScope = context.push()
+      if (pendingIdentifiers.length > 0) {
+        const newContext = newScope.addAll(pendingIdentifiers)
+        pendingIdentifiers = []
+        isInParams = false
+        return newContext
+      }
+      isInParams = false
+      return newScope
+    }
+
+    // Pop scope when exiting function
+    if (term === terms.FunctionDef) {
+      return context.pop()
+    }
+
+    // Clear stale identifiers after non-assignment statements
+    if (term === terms.PropertyAccess || term === terms.FunctionCallOrIdentifier) {
+      pendingIdentifiers = []
+    }
+
+    return context
+  },
+
+  hash: (context) => context.hash()
+})