Continue experimenting with state machines

.gitignore

@@ -1,2 +1,3 @@
 *.dSYM
 fsm
+fsm2

fsm2.c

@@ -0,0 +1,108 @@
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define ARR_LEN(X) (sizeof(X) / sizeof(X[0]))
+
+typedef enum {
+  STATE_START,
+  STATE_INVALID,
+  STATE_OBJ,
+  STATE_ARR,
+  STATE_END,
+} states;
+
+states handle_start(char input);
+states handle_obj(char input);
+states handle_arr(char input);
+
+states state_machine(states current, char input);
+
+bool check_input(const char *text);
+
+// clang-format off
+const char *inputs[] = {
+	"{}",
+	"[]",
+	"{           }",
+	"[         ]",
+	"           {}",
+	"           []",
+	"{}              ",
+	"[]              ",
+	"{",
+	"[",
+	"}",
+	"]",
+	"{f}",
+	"[8]",
+};
+// clang-format on
+
+int main(int argc, char *argv[]) {
+  for (int i = 0; i < ARR_LEN(inputs); ++i) {
+    printf("%20s is %s\n", inputs[i],
+           check_input(inputs[i]) ? "VALID" : "INVALID");
+  }
+
+  return EXIT_SUCCESS;
+}
+
+bool check_input(const char *text) {
+  states current = STATE_START;
+
+  for (const char *c = &(text[0]); *c != '\0'; ++c) {
+    current = state_machine(current, *c);
+  }
+
+  return current == STATE_END;
+}
+
+states handle_start(char input) {
+  if (isspace(input)) {
+    return STATE_START;
+  }
+
+  switch (input) {
+  case '{':
+    return STATE_OBJ;
+  case '[':
+    return STATE_ARR;
+  default:
+    return STATE_INVALID;
+  }
+}
+
+states handle_obj(char input) {
+  if (isspace(input)) {
+    return STATE_OBJ;
+  } else if (input == '}') {
+    return STATE_END;
+  }
+
+  return STATE_INVALID;
+}
+
+states handle_arr(char input) {
+  if (isspace(input)) {
+    return STATE_ARR;
+  } else if (input == ']') {
+    return STATE_END;
+  }
+
+  return STATE_INVALID;
+}
+
+states state_machine(states current, char input) {
+  switch (current) {
+  case STATE_START:
+    return handle_start(input);
+  case STATE_OBJ:
+    return handle_obj(input);
+  case STATE_ARR:
+    return handle_arr(input);
+  default:
+    return current;
+  }
+}