From 0eb3d602df451f882e107ebed47b3bce9a1e68dc Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Sat, 19 Dec 2009 20:44:53 -0500
Subject: Make symbol table semantics line up with povray's.

---
 dimension/grammar.y |  2 +-
 dimension/main.c    |  2 +-
 dimension/parse.c   | 71 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 dimension/parse.h   |  8 ++++--
 dimension/realize.c |  3 ++-
 5 files changed, 75 insertions(+), 11 deletions(-)

diff --git a/dimension/grammar.y b/dimension/grammar.y
index 7955476..e52d668 100644
--- a/dimension/grammar.y
+++ b/dimension/grammar.y
@@ -1134,7 +1134,7 @@ dmnsn_parse(FILE *file, dmnsn_symbol_table *symtable)
     filename = fnode->ptr;
   } else {
     filename = "<>";
-    dmnsn_push_symbol(symtable, "__file__", dmnsn_new_ast_string(filename));
+    dmnsn_declare_symbol(symtable, "__file__", dmnsn_new_ast_string(filename));
   }
 
   void *scanner;
diff --git a/dimension/main.c b/dimension/main.c
index 561ee99..9083a07 100644
--- a/dimension/main.c
+++ b/dimension/main.c
@@ -157,7 +157,7 @@ main(int argc, char **argv) {
 
   /* Construct the symbol table */
   dmnsn_symbol_table *symtable = dmnsn_new_symbol_table();
-  dmnsn_push_symbol(symtable, "__file__", dmnsn_new_ast_string(input));
+  dmnsn_declare_symbol(symtable, "__file__", dmnsn_new_ast_string(input));
 
   /* Debugging option - output the abstract syntax tree as an S-expression */
   if (parse) {
diff --git a/dimension/parse.c b/dimension/parse.c
index 0bc080f..1916941 100644
--- a/dimension/parse.c
+++ b/dimension/parse.c
@@ -116,15 +116,20 @@ dmnsn_new_symbol_table()
   return symtable;
 }
 
+static void
+dmnsn_delete_symbol(dmnsn_symbol symbol)
+{
+  free(symbol.id);
+  dmnsn_delete_astnode(symbol.value);
+}
+
 static void
 dmnsn_delete_scope(dmnsn_array *scope)
 {
   while (dmnsn_array_size(scope) > 0) {
     dmnsn_symbol symbol;
     dmnsn_array_pop(scope, &symbol);
-
-    free(symbol.id);
-    dmnsn_delete_astnode(symbol.value);
+    dmnsn_delete_symbol(symbol);
   }
   dmnsn_delete_array(scope);
 }
@@ -154,18 +159,72 @@ void dmnsn_pop_scope(dmnsn_symbol_table *symtable)
   dmnsn_delete_scope(scope);
 }
 
-void dmnsn_push_symbol(dmnsn_symbol_table *symtable,
-                       const char *id, dmnsn_astnode value)
+void dmnsn_local_symbol(dmnsn_symbol_table *symtable,
+                        const char *id, dmnsn_astnode value)
 {
   ++*value.refcount;
 
   dmnsn_array *scope;
   dmnsn_array_get(symtable, dmnsn_array_size(symtable) - 1, &scope);
 
+  unsigned int i;
+  for (i = 0; i < dmnsn_array_size(scope); ++i) {
+    dmnsn_symbol *symbol = dmnsn_array_at(scope,
+                                          dmnsn_array_size(scope) - i - 1);
+
+    if (strcmp(id, symbol->id) == 0) {
+      dmnsn_delete_astnode(symbol->value);
+      symbol->value = value;
+      return;
+    }
+  }
+
   dmnsn_symbol symbol = { .id = strdup(id), .value = value };
   dmnsn_array_push(scope, &symbol);
 }
 
+void
+dmnsn_declare_symbol(dmnsn_symbol_table *symtable,
+                     const char *id, dmnsn_astnode value)
+{
+  ++*value.refcount;
+
+  dmnsn_astnode *node = dmnsn_find_symbol(symtable, id);
+  if (node) {
+    /* Always update the most local symbol */
+    dmnsn_delete_astnode(*node);
+    *node = value;
+  } else {
+    /* but create new ones at the least local scope */
+    dmnsn_array *scope;
+    dmnsn_array_get(symtable, 0, &scope);
+
+    dmnsn_symbol symbol = { .id = strdup(id), .value = value };
+    dmnsn_array_push(scope, &symbol);
+  }
+}
+
+void
+dmnsn_undef_symbol(dmnsn_symbol_table *symtable, const char *id)
+{
+  unsigned int i;
+  for (i = 0; i < dmnsn_array_size(symtable); ++i) {
+    dmnsn_array *scope;
+    dmnsn_array_get(symtable, dmnsn_array_size(symtable) - i - 1, &scope);
+
+    unsigned int j;
+    for (j = 0; j < dmnsn_array_size(scope); ++j) {
+      dmnsn_symbol *symbol = dmnsn_array_at(scope,
+                                            dmnsn_array_size(scope) - j - 1);
+
+      if (strcmp(id, symbol->id) == 0) {
+        dmnsn_array_remove(scope, j);
+        return;
+      }
+    }
+  }
+}
+
 dmnsn_astnode *
 dmnsn_find_symbol(dmnsn_symbol_table *symtable, const char *id)
 {
@@ -175,7 +234,7 @@ dmnsn_find_symbol(dmnsn_symbol_table *symtable, const char *id)
     dmnsn_array_get(symtable, dmnsn_array_size(symtable) - i - 1, &scope);
 
     unsigned int j;
-    for (j = 0; j < dmnsn_array_size(symtable); ++j) {
+    for (j = 0; j < dmnsn_array_size(scope); ++j) {
       dmnsn_symbol *symbol = dmnsn_array_at(scope,
                                             dmnsn_array_size(scope) - j - 1);
 
diff --git a/dimension/parse.h b/dimension/parse.h
index 6f8755d..6f5b981 100644
--- a/dimension/parse.h
+++ b/dimension/parse.h
@@ -115,8 +115,12 @@ void dmnsn_delete_symbol_table(dmnsn_symbol_table *symtable);
 void dmnsn_push_scope(dmnsn_symbol_table *symtable);
 void dmnsn_pop_scope(dmnsn_symbol_table *symtable);
 
-void dmnsn_push_symbol(dmnsn_symbol_table *symtable,
-                       const char *id, dmnsn_astnode value);
+void dmnsn_local_symbol(dmnsn_symbol_table *symtable,
+                        const char *id, dmnsn_astnode value);
+void dmnsn_declare_symbol(dmnsn_symbol_table *symtable,
+                          const char *id, dmnsn_astnode value);
+void dmnsn_undef_symbol(dmnsn_symbol_table *symtable, const char *id);
+
 dmnsn_astnode *dmnsn_find_symbol(dmnsn_symbol_table *symtable, const char *id);
 
 /* Evaluate an arithmetic expression */
diff --git a/dimension/realize.c b/dimension/realize.c
index eda7056..5a13d8b 100644
--- a/dimension/realize.c
+++ b/dimension/realize.c
@@ -636,7 +636,8 @@ dmnsn_realize_string(const char *str, dmnsn_symbol_table *symtable)
     symtable = dmnsn_new_symbol_table();
   }
   if (!dmnsn_find_symbol(symtable, "__file__")) {
-    dmnsn_push_symbol(symtable, "__file__", dmnsn_new_ast_string("<string>"));
+    dmnsn_declare_symbol(symtable, "__file__",
+                         dmnsn_new_ast_string("<string>"));
   }
 
   FILE *file = fmemopen((void *)str, strlen(str), "r");
-- 
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