minimal lr parser

1 files changed, 145 insertions, 0 deletions

diff --git a/lr-parser.c b/lr-parser.c
new file mode 100644
index 0000000..3b0ecb7
--- /dev/null
+++ b/lr-parser.c
@@ -0,0 +1,145 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef unsigned int symbol;
+// extern const size_t total_symbols;
+
+// extern int symbol_is_terminal(symbol s);
+// extern int symbol_is_input_end(symbol s);
+extern int symbol_is_valid(symbol s);
+
+extern struct production {
+    symbol LHS;
+    symbol *RHS;
+    size_t nRHS;
+} grammar[];
+extern const size_t total_productions;
+// extern void grammar_print();
+
+struct action {
+    enum action_type {
+        ACTION_NOT_SET = 0, ACTION_SHIFT,
+        ACTION_GOTO, ACTION_REDUCE,
+        ACTION_ACCEPT
+    } type;
+    size_t arg;
+};
+
+extern struct action *table[];
+extern size_t table_states;
+// extern void table_print();
+
+extern symbol toklist_eat();
+extern symbol toklist_peek();
+
+typedef int stack_item;
+
+#define STACK_CAP 128
+stack_item stack_bottom[STACK_CAP];
+stack_item *stack_head = stack_bottom;
+
+int lr_parser()
+{
+#define push(item) ({ if(++stack_head - stack_bottom < STACK_CAP ) (*stack_head = item); else { fprintf(stderr, "ERROR: STACK_CAP exceeded"); return 1; }})
+#define pop() (--stack_head)
+#define eat() toklist_eat()
+#define peek() ({ symbol s = toklist_peek(); if(!symbol_is_valid(s)) return 1; s; })
+    
+    while(1) {
+        struct action a = table[(size_t)*stack_head][peek()];
+        
+        switch(a.type) {
+        case ACTION_SHIFT:
+            push(eat());
+            push(a.arg);
+            break;
+        case ACTION_REDUCE:
+            for(size_t i = 0; i < 2*grammar[a.arg].nRHS; i++) pop();
+            
+            symbol lhs = grammar[a.arg].LHS;
+            struct action a_goto = table[(size_t)*stack_head][lhs];
+            if(a_goto.type != ACTION_GOTO) {
+                fprintf(stderr,
+                        "ERROR: Expected goto action for symbol %d at state %zu",
+                        lhs, (size_t)*stack_head);
+                return 1;
+            }
+            
+            push(lhs);
+            push(a_goto.arg);
+            break;
+        case ACTION_ACCEPT:
+            return 0;
+        case ACTION_NOT_SET:
+        default:
+            fprintf(stderr,
+                    "ERROR: Unexpected error symbol %d at state %zu",
+                    peek(), (size_t)*stack_head);
+            return 1;
+        }
+    }
+
+    return 1;
+}
+
+#ifdef _LR_PARSER_STANDALONE
+
+enum symbol {
+    PLUS = 0,
+    MINUS,
+    LPAREN,
+    RPAREN,
+    N0, N1,
+    END_INPUT,
+
+    EP, E, T, N,
+    SYMBOLS_END,
+};
+
+const size_t total_symbols = SYMBOLS_END;
+
+int symbol_is_valid(symbol s)   { return s < SYMBOLS_END; }
+
+#define PROD(LHS, _, ...) {LHS, (symbol[]){__VA_ARGS__}, sizeof((symbol[]){__VA_ARGS__})/sizeof(symbol)}
+struct production grammar[] = {
+    PROD(EP, ->, E, END_INPUT),
+    PROD(E, -->, E, PLUS, T),
+    PROD(E, -->, E, MINUS, T),
+    PROD(E, -->, T),
+    PROD(T, -->, LPAREN, E, RPAREN),
+    PROD(T, -->, N),
+    PROD(N, -->, N0),
+    PROD(N, -->, N1),
+};
+
+const size_t total_productions = sizeof(grammar)/sizeof(*grammar);
+
+struct action *table[] = {
+    (struct action[]){{0, 0},{0, 0},{1, 1},{0, 0},{1, 2},{1, 3},{0, 0},{0, 0},{2, 12},{2, 11},{2, 7},},
+    (struct action[]){{0, 0},{0, 0},{1, 1},{0, 0},{1, 2},{1, 3},{0, 0},{0, 0},{2, 4},{2, 11},{2, 7},},
+    (struct action[]){{3, 6},{3, 6},{0, 0},{3, 6},{0, 0},{0, 0},{3, 6},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{3, 7},{3, 7},{0, 0},{3, 7},{0, 0},{0, 0},{3, 7},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{1, 5},{1, 8},{0, 0},{1, 10},{0, 0},{0, 0},{0, 0},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{0, 0},{0, 0},{1, 1},{0, 0},{1, 2},{1, 3},{0, 0},{0, 0},{0, 0},{2, 6},{2, 7},},
+    (struct action[]){{3, 1},{3, 1},{0, 0},{3, 1},{0, 0},{0, 0},{3, 1},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{3, 5},{3, 5},{0, 0},{3, 5},{0, 0},{0, 0},{3, 5},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{0, 0},{0, 0},{1, 1},{0, 0},{1, 2},{1, 3},{0, 0},{0, 0},{0, 0},{2, 9},{2, 7},},
+    (struct action[]){{3, 2},{3, 2},{0, 0},{3, 2},{0, 0},{0, 0},{3, 2},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{3, 4},{3, 4},{0, 0},{3, 4},{0, 0},{0, 0},{3, 4},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{3, 3},{3, 3},{0, 0},{3, 3},{0, 0},{0, 0},{3, 3},{0, 0},{0, 0},{0, 0},{0, 0},},
+    (struct action[]){{1, 5},{1, 8},{0, 0},{0, 0},{0, 0},{0, 0},{4, 0},{0, 0},{0, 0},{0, 0},{0, 0},},
+};
+size_t table_states = 13;
+
+symbol toklist[] = {N0, PLUS, N1, END_INPUT};
+symbol *tok = toklist;
+
+symbol toklist_eat() { return *(tok++); }
+symbol toklist_peek() { return *tok; }
+
+int main(void)
+{
+    return lr_parser();
+}
+
+#endif