From 8f63364c2b1ec54e104c189db43805917800b789 Mon Sep 17 00:00:00 2001
From: sanine <sanine.not@pm.me>
Date: Mon, 27 Oct 2025 10:52:01 -0500
Subject: implement basic grammatical expansion

---
 expression.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 100 insertions(+), 5 deletions(-)

(limited to 'expression.c')

diff --git a/expression.c b/expression.c
index 11904fc..f4d7b26 100644
--- a/expression.c
+++ b/expression.c
@@ -1,5 +1,6 @@
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 #include "expression.h"
 
 
@@ -65,7 +66,7 @@ int li_prod_rule_add(
 }
 
 
-li_grammar_t * li_grammar_alloc(size_t num_nonterminal) {
+li_grammar_t * li_grammar_alloc(int num_nonterminal) {
   li_grammar_t *grammar = malloc(sizeof(li_grammar_t));
   if (grammar == NULL) {
     fprintf(stderr, "failed to allocate grammar\n");
@@ -77,18 +78,18 @@ li_grammar_t * li_grammar_alloc(size_t num_nonterminal) {
     free(grammar);
     return NULL;
   }
-  for (size_t i=0; i<num_nonterminal; i++) {
+  for (int i=0; i<num_nonterminal; i++) {
     grammar->rules[i].num_productions = 0;
     grammar->rules[i].head = NULL;
   }
-  grammar->num_nonterminal = NULL;
+  grammar->num_nonterminal = num_nonterminal;
   return grammar;
 }
 
 
 void li_grammar_free(li_grammar_t *grammar) {
   if (grammar != NULL) {
-    for (size_t i=0; i<grammar->num_nonterminal; i++) {
+    for (int i=0; i<grammar->num_nonterminal; i++) {
       li_production_free(grammar->rules[i].head);
     }
     free(grammar->rules);
@@ -100,7 +101,7 @@ void li_grammar_free(li_grammar_t *grammar) {
 int li_grammar_rule_add(
   li_grammar_t *grammar, int nonterminal, size_t seq_len, int *seq
 ) {
-  if (nonterminal < 0 || nonterminal >= grammar->num_nonterminal) {
+  if (nonterminal >= grammar->num_nonterminal) {
     return 2;
   }
   return li_prod_rule_add(grammar->rules + nonterminal, seq_len, seq);
@@ -108,3 +109,97 @@ int li_grammar_rule_add(
 
 
 
+int stack_push(int *stack, size_t stack_sz, size_t *top, int value) {
+  *top += 1;
+  if (*top >= stack_sz) {
+    fprintf(stderr, "grammar stack overflow!\n");
+    return 1;
+  }
+  stack[*top] = value;
+  return 0;
+}
+
+
+int stack_pop(int *stack, size_t *top, int *value) {
+  if (*top == ((size_t)-1)) {
+    fprintf(stderr, "grammar stack underflow!\n");
+    return 1;
+  }
+
+  *value = stack[*top];
+  *top -=1;
+  return 0;
+}
+
+
+int expand_production(
+  li_grammar_t *grammar, 
+  int *dst, size_t sz, size_t *len,
+  int *stack, size_t stack_sz, size_t *top,
+  int symbol,
+  const uint8_t *randomness, size_t rand_sz
+) {
+  struct li_production_rule_t rule = grammar->rules[symbol];
+  struct li_production_t *prod;
+  if (rule.num_productions == 0) {
+    // empty rule, nothing to do
+    return 0;
+  } else if (rule.num_productions == 1) {
+    // pick only production
+    prod = rule.head;
+  } else {
+    // use randomness to select production
+    int selection = randomness[0] % rule.num_productions;
+    randomness += 1;
+    rand_sz -= 1;
+    prod = rule.head;
+    for (int i=0; i<selection; i++) {
+      prod = prod->next;
+    }
+  }
+
+  // push production to stack
+  for (int i=prod->seq_len-1; i>=0; i--) {
+    if (stack_push(stack, stack_sz, top, prod->seq[i]) != 0) {
+      return 1;
+    }
+  }
+
+  // pop production from stack, recursing on nonterminals
+  while (*top != ((size_t)-1)) {
+    int symbol;
+    if (stack_pop(stack, top, &symbol) != 0) {
+      return 1;
+    }
+    if (symbol < grammar->num_nonterminal) {
+      int err = expand_production(grammar, dst, sz, len, stack, stack_sz, top, symbol, randomness, rand_sz);
+      if (err != 0) {
+        return err;
+      }
+    } else {
+      if (*len > sz) {
+        fprintf(stderr, "exceeded maximum output buffer length\n");
+        return 1;
+      }
+      dst[*len] = symbol;
+      *len += 1;
+    }
+  }
+
+  return 0;
+}
+
+
+
+int li_grammar_rule_expand(
+  li_grammar_t *grammar, 
+  int *dst, size_t *len, 
+  int *stack, size_t stack_sz, 
+  int symbol, 
+  const uint8_t *randomness, size_t rand_sz
+) {
+  size_t sz = *len;
+  *len = 0;
+  size_t top = -1;
+  return expand_production(grammar, dst, sz, len, stack, stack_sz, &top, symbol, randomness, rand_sz);
+}
-- 
cgit v1.2.1