3 files changed, 74 insertions, 4 deletions

diff --git a/src/mds-kbdc/compile-layout.c b/src/mds-kbdc/compile-layout.c
index 8eac14c..477ba33 100644
--- a/src/mds-kbdc/compile-layout.c
+++ b/src/mds-kbdc/compile-layout.c
@@ -167,8 +167,8 @@ static int let(size_t variable, const char32_t* restrict string, const mds_kbdc_
   int saved_errno;
   
   /* Warn if this is a possible shadow attempt. */
-  if (possibile_shadow_attempt && variables_let_will_override(variable) &&
-      statement && (statement->processed != PROCESS_LEVEL))
+  if (possibile_shadow_attempt && variables_let_will_override(variable) && statement &&
+      (variables_has_been_used_in_for(variable) == 0) && (statement->processed != PROCESS_LEVEL))
     {
       statement->processed = PROCESS_LEVEL;
       NEW_ERROR(statement, WARNING, "does not shadow existing definition");
@@ -2110,6 +2110,7 @@ static int compile_for(mds_kbdc_tree_for_t* restrict tree)
       if (*first == *last)
 	break;
     }
+  fail_if (variables_was_used_in_for(variable));
   
   /* Catch `break` and `continue`, they may not propagate further. */
   if (break_level < 3)
diff --git a/src/mds-kbdc/variables.c b/src/mds-kbdc/variables.c
index 155edd7..4d4f941 100644
--- a/src/mds-kbdc/variables.c
+++ b/src/mds-kbdc/variables.c
@@ -41,11 +41,18 @@ typedef struct variable
   struct variable* restrict previous;
   
   /**
-   * The original scope the current shadow
-   * of the variable was created in
+   * The original scope in which the current
+   * shadow of the variable was created
    */
   size_t scope;
   
+  /**
+   * The latest scope the in which the
+   * variable has been used in a for-loop,
+   * `~0' if never, or below `scope`
+   */
+  size_t used_in_for;
+  
 } variable_t;
 
 
@@ -173,6 +180,7 @@ int variables_let(size_t variable, mds_kbdc_tree_t* restrict value)
       variables[variable]->value = value;
       variables[variable]->previous = previous;
       variables[variable]->scope = current_scope;
+      variables[variable]->used_in_for = (size_t)(~0LL);
     }
   
   return 0;
@@ -197,3 +205,49 @@ mds_kbdc_tree_t* variables_get(size_t variable)
   return variables[variable]->value;
 }
 
+
+/**
+ * Mark a variable as having been unsed in a for-loop in the current scope
+ * 
+ * @param   variable  The variable index, must already be defined
+ * @return            Zero on success, -1 on error
+ */
+int variables_was_used_in_for(size_t variable)
+{
+  variable_t* previous;
+  
+  /* Already marked. */
+  if (variables[variable]->used_in_for == current_scope)
+    return 0;
+  
+  /* Not marked. */
+  if (variables[variable]->used_in_for == (size_t)(~0LL))
+    return variables[variable]->used_in_for = current_scope, 0;
+  
+  /* Marked for another scope. */
+  previous = variables[variable];
+  if (xmalloc(variables[variable], 1, variable_t))
+    fail_if (variables[variable] = previous, 1);
+  variables[variable]->value = mds_kbdc_tree_dup(previous->value);
+  fail_if (variables[variable]->value == NULL);
+  variables[variable]->previous = previous;
+  variables[variable]->scope = current_scope;
+  variables[variable]->used_in_for = current_scope;
+  
+  return 0;
+ fail:
+  return -1;
+}
+
+
+/**
+ * Check whether a variable has been used in a for-loop in the current scope
+ * 
+ * @param   variable  The variable index, must already be defined
+ * @return            Whether `variables_was_used_in_for` has been unused on the variable
+ */
+int variables_has_been_used_in_for(size_t variable)
+{
+  return variables[variable]->used_in_for == current_scope;
+}
+
diff --git a/src/mds-kbdc/variables.h b/src/mds-kbdc/variables.h
index c01c163..c678c59 100644
--- a/src/mds-kbdc/variables.h
+++ b/src/mds-kbdc/variables.h
@@ -74,6 +74,21 @@ int variables_let(size_t variable, mds_kbdc_tree_t* restrict value);
  */
 mds_kbdc_tree_t* variables_get(size_t variable) __attribute__((pure));
 
+/**
+ * Mark a variable as having been unsed in a for-loop in the current scope
+ * 
+ * @param   variable  The variable index, must already be defined
+ * @return            Zero on success, -1 on error
+ */
+int variables_was_used_in_for(size_t variable);
+
+/**
+ * Check whether a variable has been used in a for-loop in the current scope
+ * 
+ * @param   variable  The variable index, must already be defined
+ * @return            Whether `variables_was_used_in_for` has been unused on the variable
+ */
+int variables_has_been_used_in_for(size_t variable) __attribute__((pure));
 
 
 #endif