From 11f8fd4418a068c76fc7c810967a6bf285ee74b6 Mon Sep 17 00:00:00 2001
From: sanine <sanine.not@pm.me>
Date: Mon, 27 Oct 2025 09:06:05 -0500
Subject: add expression scaffold

---
 expression.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 expression.h |  42 +++++++++++++++++++++++
 2 files changed, 152 insertions(+)
 create mode 100644 expression.c
 create mode 100644 expression.h

diff --git a/expression.c b/expression.c
new file mode 100644
index 0000000..11904fc
--- /dev/null
+++ b/expression.c
@@ -0,0 +1,110 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include "expression.h"
+
+
+struct li_production_t * li_production_alloc(size_t seq_len) {
+  struct li_production_t *prod = malloc(sizeof(struct li_production_t));
+  if (prod == NULL) {
+    fprintf(stderr, "failed to allocate production rule\n");
+    return NULL;
+  }
+  prod->seq = malloc(seq_len * sizeof(int));
+  if (prod->seq == NULL) {
+    fprintf(stderr, "failed to allocate production sequence buffer\n");
+    free(prod);
+    return NULL;
+  }
+  prod->seq_len = seq_len;
+  prod->next = NULL;
+  return prod;
+}
+
+
+void li_production_free(struct li_production_t *prod) {
+  if (prod != NULL) {
+    li_production_free(prod->next);
+    free(prod->seq);
+    free(prod);
+  }
+}
+
+
+struct li_production_rule_t * li_prod_rule_alloc() {
+  struct li_production_rule_t *rule = malloc(sizeof(struct li_production_rule_t));
+  if (rule == NULL) {
+    fprintf(stderr, "failed to allocate production rule\n");
+    return NULL;
+}
+  rule->num_productions = 0;
+  rule->head = NULL;
+  return rule;
+}
+
+
+void li_prod_rule_free(struct li_production_rule_t *rule) {
+  if (rule != NULL) {
+    li_production_free(rule->head);
+    free(rule);
+  }
+}
+
+
+int li_prod_rule_add(
+  struct li_production_rule_t *rule, size_t seq_len, int *seq
+) {
+  struct li_production_t *prod = li_production_alloc(seq_len);
+  if (prod == NULL) {
+    return 1;
+  }
+  memcpy(prod->seq, seq, seq_len*sizeof(int));
+  prod->next = rule->head;
+  rule->head = prod;
+  rule->num_productions += 1;
+  return 0;
+}
+
+
+li_grammar_t * li_grammar_alloc(size_t num_nonterminal) {
+  li_grammar_t *grammar = malloc(sizeof(li_grammar_t));
+  if (grammar == NULL) {
+    fprintf(stderr, "failed to allocate grammar\n");
+    return NULL;
+  }
+  grammar->rules = malloc(num_nonterminal * sizeof(struct li_production_rule_t));
+  if (grammar->rules == NULL) {
+    fprintf(stderr, "failed to allocate grammar rules buffer\n");
+    free(grammar);
+    return NULL;
+  }
+  for (size_t i=0; i<num_nonterminal; i++) {
+    grammar->rules[i].num_productions = 0;
+    grammar->rules[i].head = NULL;
+  }
+  grammar->num_nonterminal = NULL;
+  return grammar;
+}
+
+
+void li_grammar_free(li_grammar_t *grammar) {
+  if (grammar != NULL) {
+    for (size_t i=0; i<grammar->num_nonterminal; i++) {
+      li_production_free(grammar->rules[i].head);
+    }
+    free(grammar->rules);
+    free(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) {
+    return 2;
+  }
+  return li_prod_rule_add(grammar->rules + nonterminal, seq_len, seq);
+}
+
+
+
diff --git a/expression.h b/expression.h
new file mode 100644
index 0000000..36a0e02
--- /dev/null
+++ b/expression.h
@@ -0,0 +1,42 @@
+#ifndef LICHEN_EXPRESSION_H
+#define LICHEN_EXPRESSION_H
+
+/****************************************************************
+ * 
+ * a grammar is built on both nonterminals and terminals. both are
+ * represented by integers; nonterminals must be less than MAX_NONTERMINAL
+ * and terminals must be greater. the intended way to do this is to define
+ * an enum with all symbols, and have a MAX_NONTERMINAL symbol dividing the
+ * (low) nonterminals from the (high) terminals.
+ *
+ ****************************************************************
+ */
+
+struct li_production_t {
+  int *seq;
+  size_t seq_len;
+  struct li_production_t *next;  
+};
+
+struct li_production_t * li_production_alloc(size_t seq_len);
+void li_production_free(struct li_production_t *prod);
+
+struct li_production_rule_t {
+  size_t num_productions;
+  struct li_production_t *head;
+};
+
+struct li_production_rule_t * li_prod_rule_alloc();
+void li_prod_rule_free(struct li_production_rule_t *rule);
+int li_prod_rule_add(struct li_production_rule_t *rule, size_t seq_len, int *seq);
+
+typedef struct li_grammar_t {
+  struct li_production_rule_t *rules;
+  size_t num_nonterminal;
+} li_grammar_t;
+
+li_rammar_t * li_grammar_alloc(size_t num_nonterminal);
+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);
+
+#endif
-- 
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