backward inference

fold.cm

@@ -15,10 +15,18 @@ var fold = function(ast) {
     return k == "number" || k == "text" || k == "true" || k == "false" || k == "null"
   }
 
+  // Only intrinsics that can NEVER disrupt regardless of argument types
+  var pure_intrinsics = {
+    is_array: true, is_text: true, is_number: true, is_integer: true,
+    is_function: true, is_logical: true, is_null: true, is_object: true,
+    is_stone: true
+  }
+
   var is_pure = function(expr) {
     if (expr == null) return true
     var k = expr.kind
     var i = 0
+    var target = null
     if (k == "number" || k == "text" || k == "true" || k == "false" ||
         k == "null" || k == "name" || k == "this") return true
     if (k == "function") return true
@@ -47,6 +55,17 @@ var fold = function(ast) {
     if (k == "==" || k == "!=" || k == "&&" || k == "||") {
       return is_pure(expr.left) && is_pure(expr.right)
     }
+    if (k == "(") {
+      target = expr.expression
+      if (target != null && target.intrinsic == true && pure_intrinsics[target.name] == true) {
+        i = 0
+        while (i < length(expr.list)) {
+          if (!is_pure(expr.list[i])) return false
+          i = i + 1
+        }
+        return true
+      }
+    }
     return false
   }
 
@@ -676,6 +695,10 @@ var fold = function(ast) {
           }
         }
       }
+      // Dead pure call elimination: standalone pure calls with no result
+      if (stmt.kind == "call" && is_pure(stmt.expression)) {
+        stmt.dead = true
+      }
       // Dead function elimination
       if (stmt.kind == "function" && stmt.name != null) {
         sv = scope_var(fn_nr, stmt.name)