Create environment module

lib/env.c

@@ -0,0 +1,80 @@
+#include "env.h"
+
+#include <assert.h>
+#include <string.h>
+
+static bool symbol_eq(symbol_t *s, symbol_t *t)
+{
+	return s->len == t->len && memcmp(s->buf, t->buf, s->len) == 0;
+}
+
+static expr_t **lookup(am_t *am, bool *found)
+{
+	assert(am->expr != NULL);
+	assert(am->expr->is_atom);
+	assert(am->expr->atom.type == ATOM_TYPE_SYMBOL);
+
+	if (am->env->is_atom) {
+		assert(am->env->atom.type == ATOM_TYPE_EMPTY_LIST);
+		*found = false;
+		return &am->env;
+	}
+
+	expr_t *prev;
+	for (expr_t *list = am->env; !list->is_atom; list = list->pair.cdr) {
+		assert(list != NULL);
+
+		expr_t *entry = list->pair.car;
+		assert(!entry->is_atom);
+
+		expr_t *key = entry->pair.car;
+		assert(key != NULL);
+		assert(key->is_atom);
+		assert(key->atom.type == ATOM_TYPE_SYMBOL);
+
+		if (symbol_eq(&am->expr->atom.symbol, &key->atom.symbol)) {
+			*found = true;
+			return &entry->pair.cdr;
+		}
+
+		prev = list;
+	}
+
+	assert(!prev->is_atom);
+	assert(prev->pair.cdr->is_atom);
+	assert(prev->pair.cdr->atom.type == ATOM_TYPE_EMPTY_LIST);
+	*found = false;
+	return &prev->pair.cdr;
+}
+
+void env_init(am_t *am, store_t *store)
+{
+	am->env = store_alloc(store);
+	am->env->is_atom = true;
+	am->env->atom.type = ATOM_TYPE_EMPTY_LIST;
+}
+
+void env_fetch(am_t *am)
+{
+	bool found;
+	expr_t *val = *lookup(am, &found);
+	am->val = found ? val : NULL;
+}
+
+void env_set(am_t *am, store_t *store)
+{
+	bool found;
+	expr_t **loc = lookup(am, &found);
+	if (found) {
+		*loc = am->val;
+	} else {
+		(*loc)->is_atom = false;
+		(*loc)->pair.cdr = store_alloc(store);
+		(*loc)->pair.cdr->is_atom = true;
+		(*loc)->pair.cdr->atom.type = ATOM_TYPE_EMPTY_LIST;
+
+		expr_t *entry = (*loc)->pair.car = store_alloc(store);
+		entry->pair.car = am->expr;
+		entry->pair.cdr = am->val;
+	}
+}