quick and easy semantic actions

1 files changed, 11 insertions, 2 deletions

diff --git a/lr-parser.c b/lr-parser.c
index 3ab9af4..f7197c5 100644
--- a/lr-parser.c
+++ b/lr-parser.c
@@ -9,6 +9,9 @@
 #include "parts/grammar.h"
 #include "parts/table.h"
 #include "parts/toklist.h"
+// and
+typedef int (*semantic_action_fn)(int *stack_head);
+extern semantic_action_fn *semantic_actions;
 
 typedef int stack_item;
 
@@ -32,10 +35,12 @@ int lr_parser()
         switch(a.type) {
         case ACTION_SHIFT:
             push(eat());
+            push(-10000000); // the semantic action
             push(a.arg);
             break;
         case ACTION_REDUCE:
-            for(size_t i = 0; i < 2*grammar[a.arg].nRHS; i++) pop();
+            int semantic_value = semantic_actions[a.arg](stack_head);
+            for(size_t i = 0; i < 3*grammar[a.arg].nRHS; i++) pop();
 
             symbol lhs = grammar[a.arg].LHS;
             struct action a_goto = table[(size_t)*stack_head][lhs];
@@ -47,10 +52,11 @@ int lr_parser()
             }
 
             push(lhs);
+            push(semantic_value);
             push(a_goto.arg);
             break;
         case ACTION_ACCEPT:
-            return 0;
+            return *(stack_head-1);
         case ACTION_NOT_SET:
         default:
             fprintf(stderr,
@@ -124,6 +130,9 @@ static symbol *tok = toklist;
 symbol toklist_eat() { return *(tok++); } // unsafe
 symbol toklist_peek() { return *tok; }    // unsafe
 
+int none(int *stack_head) {(void)stack_head; return 0;};
+semantic_action_fn *semantic_actions = (semantic_action_fn[]){none, none, none, none, none, none, none, none};
+
 int main(void)
 {
     return lr_parser();