Data commit

Task/Monads-Maybe-monad/C/monads-maybe-monad.c

@@ -0,0 +1,124 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+typedef enum type
+{
+  INT,
+  STRING
+} Type;
+
+typedef struct maybe
+{
+  int i;
+  char *s;
+  Type t;
+  _Bool is_something;
+} Maybe;
+
+void print_Maybe(Maybe *m)
+{
+  if (m->t == INT)
+    printf("Just %d : INT\n", m->i);
+
+  else if (m->t == STRING)
+    printf("Just \"%s\" : STRING\n", m->s);
+
+  else
+    printf("Nothing\n");
+
+}
+
+Maybe *return_maybe(void *data, Type t)
+{
+  Maybe *m = malloc(sizeof(Maybe));
+  if (t == INT)
+  {
+    m->i = *(int *) data;
+    m->s = NULL;
+    m->t = INT;
+    m->is_something = true;
+  }
+
+  else if (t == STRING)
+  {
+    m->i = 0;
+    m->s = data;
+    m->t = STRING;
+    m->is_something = true;
+  }
+
+  else
+  {
+    m->i = 0;
+    m->s = NULL;
+    m->t = 0;
+    m->is_something = false;
+  }
+
+  return m;
+}
+
+Maybe *bind_maybe(Maybe *m, Maybe *(*f)(void *))
+{
+  Maybe *n = malloc(sizeof(Maybe));
+
+  if (f(&(m->i))->is_something)
+  {
+    n->i = f(&(m->i))->i;
+    n->s = f(&(m->i))->s;
+    n->t = f(&(m->i))->t;
+    n->is_something = true;
+  }
+
+  else
+  {
+    n->i = 0;
+    n->s = NULL;
+    n->t = 0;
+    n->is_something = false;
+  }
+  return n;
+}
+
+Maybe *f_1(void *v) // Int -> Maybe Int
+{
+  Maybe *m = malloc(sizeof(Maybe));
+  m->i = (*(int *) v) * (*(int *) v);
+  m->s = NULL;
+  m->t = INT;
+  m->is_something = true;
+  return m;
+}
+
+Maybe *f_2(void *v) // :: Int -> Maybe String
+{
+  Maybe *m = malloc(sizeof(Maybe));
+  m->i = 0;
+  m->s = malloc(*(int *) v * sizeof(char) + 1);
+  for (int i = 0; i < *(int *) v; i++)
+  {
+    m->s[i] = 'x';
+  }
+  m->s[*(int *) v + 1] = '\0';
+  m->t = STRING;
+  m->is_something = true;
+  return m;
+}
+
+int main()
+{
+  int i = 7;
+  char *s = "lorem ipsum dolor sit amet";
+
+  Maybe *m_1 = return_maybe(&i, INT);
+  Maybe *m_2 = return_maybe(s, STRING);
+
+  print_Maybe(m_1); // print value of m_1: Just 49
+  print_Maybe(m_2); // print value of m_2 : Just "lorem ipsum dolor sit amet"
+
+  print_Maybe(bind_maybe(m_1, f_1)); // m_1 `bind` f_1 :: Maybe Int
+  print_Maybe(bind_maybe(m_1, f_2)); // m_1 `bind` f_2 :: Maybe String
+
+  print_Maybe(bind_maybe(bind_maybe(m_1, f_1), f_2)); // (m_1 `bind` f_1) `bind` f_2 :: Maybe String -- it prints 49 'x' characters in a row
+}