fix compilation error

CLAUDE.md

@@ -179,6 +179,26 @@ When running locally with `./cell --dev`, these commands manage packages:
 
 Local paths are symlinked into `.cell/packages/`. The build step compiles C files to `.cell/lib/<pkg>/<stem>.dylib`. C files in `src/` are support files linked into module dylibs, not standalone modules.
 
+## Debugging Compiler Issues
+
+When investigating bugs in compiled output (wrong values, missing operations, incorrect comparisons), **start from the optimizer down, not the VM up**. The compiler inspection tools will usually identify the problem faster than adding C-level tracing:
+
+```
+./cell --dev streamline --types <file>    # show inferred slot types — look for wrong types
+./cell --dev ir_report --events <file>    # show every optimization applied and why
+./cell --dev ir_report --types <file>     # show type inference results per function
+./cell --dev mcode --pretty <file>        # show raw IR before optimization
+./cell --dev streamline --ir <file>       # show human-readable optimized IR
+```
+
+**Triage order:**
+1. `streamline --types` — are slot types correct? Wrong type inference causes wrong optimizations.
+2. `ir_report --events` — are type checks being incorrectly eliminated? Look for `known_type_eliminates_guard` on slots that shouldn't have known types.
+3. `mcode --pretty` — is the raw IR correct before optimization? If so, the bug is in streamline.
+4. Only dig into `source/mach.c` if the IR looks correct at all levels.
+
+See `docs/compiler-tools.md` for the full tool reference and `docs/spec/streamline.md` for pass details.
+
 ## Testing
 
 After any C runtime changes, run all three test suites before considering the work done:

docs/spec/pipeline.md

@@ -62,12 +62,13 @@ See [Mcode IR](mcode.md) for the instruction format and complete instruction ref
 Optimizes the Mcode IR through a series of independent passes. Operates per-function:
 
 1. **Backward type inference**: Infers parameter types from how they are used in typed operators (`add_int`, `store_index`, `load_field`, `push`, `pop`, etc.). Immutable `def` parameters keep their inferred type across label join points.
-2. **Type-check elimination**: When a slot's type is known, eliminates `is_<type>` + conditional jump pairs. Narrows `load_dynamic`/`store_dynamic` to typed variants.
-3. **Algebraic simplification**: Rewrites identity operations (add 0, multiply 1, divide 1) and folds same-slot comparisons.
-4. **Boolean simplification**: Fuses `not` + conditional jump into a single jump with inverted condition.
-5. **Move elimination**: Removes self-moves (`move a, a`).
-6. **Unreachable elimination**: Nops dead code after `return` until the next label.
-7. **Dead jump elimination**: Removes jumps to the immediately following label.
+2. **Write-type invariance**: Determines which local slots have a consistent write type across all instructions. Slots written by child closures (via `put`) are excluded (forced to unknown).
+3. **Type-check elimination**: When a slot's type is known, eliminates `is_<type>` + conditional jump pairs. Narrows `load_dynamic`/`store_dynamic` to typed variants.
+4. **Algebraic simplification**: Rewrites identity operations (add 0, multiply 1, divide 1) and folds same-slot comparisons.
+5. **Boolean simplification**: Fuses `not` + conditional jump into a single jump with inverted condition.
+6. **Move elimination**: Removes self-moves (`move a, a`).
+7. **Unreachable elimination**: Nops dead code after `return` until the next label.
+8. **Dead jump elimination**: Removes jumps to the immediately following label.
 
 See [Streamline Optimizer](streamline.md) for detailed pass descriptions.
 

docs/spec/streamline.md

@@ -95,7 +95,9 @@ Write type mapping:
 | `move`, `load_field`, `load_index`, `load_dynamic`, `pop`, `get` | T_UNKNOWN |
 | `invoke`, `tail_invoke` | T_UNKNOWN |
 
-The result is a map of slot→type for slots where all writes agree on a single known type. Parameter slots (1..nr_args) and slot 0 are excluded.
+Before filtering, a pre-pass (`mark_closure_writes`) scans all inner functions for `put` instructions (closure variable writes). For each `put`, the pass traverses the parent chain to find the target ancestor function and marks the written slot as `closure_written`. Slots marked as closure-written are forced to T_UNKNOWN regardless of what the local write analysis infers, because the actual runtime write happens in a child function and can produce any type.
+
+The result is a map of slot→type for slots where all writes agree on a single known type. Parameter slots (1..nr_args) and slot 0 are excluded. Closure-written slots are excluded (forced to unknown).
 
 Common patterns this enables:
 

internal/engine.cm

@@ -78,6 +78,7 @@ function load_pipeline_module(name, env) {
   var boot_par = null
   var boot_fld = null
   var boot_mc = null
+  var boot_sl = null
   var tok_result = null
   var ast = null
   var compiled = null
@@ -105,6 +106,8 @@ function load_pipeline_module(name, env) {
       }
       ast = boot_fld(ast)
       compiled = boot_mc(ast)
+      boot_sl = boot_load("streamline")
+      compiled = boot_sl(compiled)
       mcode_json = json.encode(compiled)
       mach_blob = mach_compile_mcode_bin(name, mcode_json)
       if (cached) {

seed.ce

@@ -54,6 +54,7 @@ var compiled = null
 var optimized = null
 var mcode_json = null
 var out_path = null
+var build_dir = null
 
 // Regenerate pipeline module seeds
 for (i = 0; i < length(pipeline_modules); i++) {
@@ -103,7 +104,7 @@ if (fd.is_file(bootstrap_path)) {
 print('\nRegenerated ' + text(generated) + ' seed(s)')
 
 if (clean) {
-  var build_dir = shop.get_build_dir()
+  build_dir = shop.get_build_dir()
   if (fd.is_dir(build_dir)) {
     print('Clearing build cache: ' + build_dir)
     os.system('rm -rf "' + build_dir + '"')

streamline.cm

@@ -336,6 +336,7 @@ var streamline = function(ir, log) {
     var slot = 0
     var typ = null
     var rule = null
+    var cw_keys = null
 
     if (instructions == null) {
       return array(func.nr_slots)
@@ -362,6 +363,19 @@ var streamline = function(ir, log) {
       i = i + 1
     }
 
+    // Closure-written slots can have any type at runtime — mark unknown
+    if (func.closure_written != null) {
+      cw_keys = array(func.closure_written)
+      k = 0
+      while (k < length(cw_keys)) {
+        slot = number(cw_keys[k])
+        if (slot >= 0 && slot < length(write_types)) {
+          write_types[slot] = T_UNKNOWN
+        }
+        k = k + 1
+      }
+    }
+
     // Filter to only slots with known (non-unknown) types
     k = 0
     while (k < length(write_types)) {
@@ -1475,6 +1489,100 @@ var streamline = function(ir, log) {
     return null
   }
 
+  // =========================================================
+  // Pre-pass: mark closure-written slots
+  // Scans child functions for 'put' instructions and annotates
+  // the target ancestor func with closure_written[slot] = true.
+  // =========================================================
+  var mark_closure_writes = function(ir) {
+    var functions = ir.functions != null ? ir.functions : []
+    var fc = length(functions)
+    var parent_of = array(fc, -1)
+    var instrs = null
+    var instr = null
+    var fi = 0
+    var i = 0
+    var j = 0
+    var level = 0
+    var anc = 0
+    var slot = 0
+    var target = null
+
+    if (fc == 0) {
+      return null
+    }
+
+    // Build parent_of map
+    if (ir.main != null && ir.main.instructions != null) {
+      instrs = ir.main.instructions
+      i = 0
+      while (i < length(instrs)) {
+        instr = instrs[i]
+        if (is_array(instr) && instr[0] == "function") {
+          if (instr[2] >= 0 && instr[2] < fc) {
+            parent_of[instr[2]] = fc
+          }
+        }
+        i = i + 1
+      }
+    }
+    fi = 0
+    while (fi < fc) {
+      instrs = functions[fi].instructions
+      if (instrs != null) {
+        i = 0
+        while (i < length(instrs)) {
+          instr = instrs[i]
+          if (is_array(instr) && instr[0] == "function") {
+            if (instr[2] >= 0 && instr[2] < fc) {
+              parent_of[instr[2]] = fi
+            }
+          }
+          i = i + 1
+        }
+      }
+      fi = fi + 1
+    }
+
+    // Scan for 'put' instructions and mark ancestor slots
+    fi = 0
+    while (fi < fc) {
+      instrs = functions[fi].instructions
+      if (instrs != null) {
+        i = 0
+        while (i < length(instrs)) {
+          instr = instrs[i]
+          if (is_array(instr) && instr[0] == "put") {
+            slot = instr[2]
+            level = instr[3]
+            anc = fi
+            j = 0
+            while (j < level && anc >= 0) {
+              anc = parent_of[anc]
+              j = j + 1
+            }
+            if (anc >= 0) {
+              if (anc == fc) {
+                target = ir.main
+              } else {
+                target = functions[anc]
+              }
+              if (target != null) {
+                if (target.closure_written == null) {
+                  target.closure_written = {}
+                }
+                target.closure_written[text(slot)] = true
+              }
+            }
+          }
+          i = i + 1
+        }
+      }
+      fi = fi + 1
+    }
+    return null
+  }
+
   // =========================================================
   // Compose all passes
   // =========================================================
@@ -1530,6 +1638,12 @@ var streamline = function(ir, log) {
     return null
   }
 
+  // Pre-pass: mark slots written by child closures via 'put' instructions.
+  // Without this, infer_slot_write_types would assume those slots keep their
+  // initial type (e.g. T_NULL from 'var x = null'), causing the type-check
+  // eliminator to mis-optimize comparisons on closure-written variables.
+  mark_closure_writes(ir)
+
   // Process main function
   if (ir.main != null) {
     optimize_function(ir.main, log)

vm_suite.ce

@@ -4284,6 +4284,32 @@ run("closure set and get", function() {
   assert_eq(o.get(), 42, "overwrite")
 })
 
+run("closure write heap values visible to outer scope", function() {
+  var a = null
+  var b = null
+  var c = null
+  var d = null
+  var e = null
+  var f1 = function() { a = 42 }
+  var f2 = function() { b = true }
+  var f3 = function() { c = "hello" }
+  var f4 = function() { d = {x: 1} }
+  var f5 = function() { e = [1, 2] }
+  f1()
+  f2()
+  f3()
+  f4()
+  f5()
+  assert_eq(a, 42, "closure write number")
+  assert_eq(b, true, "closure write boolean")
+  assert_eq(c != null, true, "closure write text not null")
+  assert_eq(c, "hello", "closure write text value")
+  assert_eq(d != null, true, "closure write object not null")
+  assert_eq(d.x, 1, "closure write object property")
+  assert_eq(e != null, true, "closure write array not null")
+  assert_eq(e[0], 1, "closure write array element")
+})
+
 // ============================================================================
 // STRING COMPARISON OPERATORS
 // ============================================================================