Implement NFA construction for empty expression and literals

lib/construct.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) Camden Dixie O'Brien
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+#include "construct.h"
+
+#include <assert.h>
+#include <stdlib.h>
+
+static void construct_literal(char literal, fsa_t *out)
+{
+	fsa_init(out);
+	const int id = fsa_add_state(out);
+	fsa_add_rule(out, id, out->initial, literal);
+	out->initial = id;
+}
+
+static void construct_term(const regex_term_t *term, fsa_t *out)
+{
+	switch (term->type) {
+	case REGEX_TERM_EMPTY:
+		fsa_init(out);
+		break;
+	case REGEX_TERM_LITERAL:
+		construct_literal(term->literal, out);
+		break;
+	case REGEX_TERM_SUBEXPR:
+		return;
+
+	case REGEX_TERM_WILDCARD:
+	case REGEX_TERM_CLASS:
+		assert(false);
+	}
+}
+
+static void construct_sequence(const regex_sequence_t *seq, fsa_t *out)
+{
+	construct_term(&seq->contents[0], out);
+}
+
+void construct(const regex_t *regex, fsa_t *out)
+{
+	construct_sequence(&regex->contents[0], out);
+}

lib/construct.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) Camden Dixie O'Brien
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+#ifndef CONSTRUCT_H
+#define CONSTRUCT_H
+
+#include "fsa.h"
+#include "regex.h"
+
+void construct(const regex_t *regex, fsa_t *out);
+
+#endif