Implement some bonus marks

* Add functions cons, len & init

chapter_10/lispy.c

@@ -346,6 +346,9 @@ lval* builtin(lval* a, char* func) {
     if (strcmp("tail", func) == 0) {return builtin_tail(a);}
     if (strcmp("join", func) == 0) {return builtin_join(a);}
     if (strcmp("eval", func) == 0) {return builtin_eval(a);}
+    if (strcmp("cons", func) == 0) {return builtin_cons(a);}
+    if (strcmp("len", func) == 0)  {return builtin_len(a);}
+    if (strcmp("init", func) == 0) {return builtin_init(a);}
 
     /* Check for operators */
     if (strstr("+-*/%^", func) ||
@@ -542,6 +545,69 @@ lval* lval_join(lval* x, lval* y) {
 }
 
 
+lval* builtin_cons(lval* a) {
+
+    /* Check error conditions */
+    LASSERT(a, a->count == 2 ,
+            "Function 'cons' takes exactly 2 arguments!");
+
+    LASSERT(a, a->cell[1]->type == LVAL_QEXPR,
+            "Function 'cons' passed incorrect type!");
+
+    lval* v = lval_qexpr();
+    v = lval_add(v, lval_pop(a, 0));
+
+    lval* y = lval_pop(a, 0);
+
+    while (y->count) {
+        v = lval_add(v, lval_pop(y, 0));
+    }
+
+    lval_del(a);
+    lval_del(y);
+    return v;
+
+}
+
+
+lval* builtin_len(lval* a) {
+
+    /* Check error conditions */
+    LASSERT(a, a->count == 1,
+            "Function 'len' passed too many arguments!");
+
+    LASSERT(a, a->cell[0]->type == LVAL_QEXPR,
+        "Function 'len' passed incorrect type!");
+
+    lval* v = lval_num(a->cell[0]->count);
+    return v;
+
+}
+
+
+lval* builtin_init(lval* a) {
+
+    /* Check error conditions */
+    LASSERT(a, a->count == 1,
+            "Function 'init' passed too many arguments!");
+
+    LASSERT(a, a->cell[0]->type == LVAL_QEXPR,
+        "Function 'init' passed incorrect type!");
+
+    LASSERT(a, a->cell[0]->count != 0,
+        "Function 'init' passed {}!");
+
+    /* Otherwise take first argument */
+    lval* v = lval_take(a, 0);
+
+    /* Delete last element and return */
+    lval_del(lval_pop(v, v->count-1));
+
+    return v;
+
+}
+
+
 long min(long x, long y) {
     if (x <= y) {
         return x;

chapter_10/lispy.h

@@ -10,7 +10,8 @@ static char* parser =
 "                                                         \
     number   : /-?[0-9]+([.][0-9]*|[0-9]*)/ ;             \
     symbol : \"list\" | \"head\" | \"tail\" | \"join\" |  \
-             \"eval\" | '+' | '-' | '*' | '/' | '%' |     \
+             \"eval\" | \"len\" | \"init\" | \"cons\" |   \
+             '+' | '-' | '*' | '/' | '%' |                \
              '^' | \"min\" | \"max\" ;                    \
     sexpr    : '(' <expr>* ')' ;                          \
     qexpr    : '{' <expr>* '}' ;                          \
@@ -78,3 +79,6 @@ lval* builtin_list(lval* a);
 lval* builtin_eval(lval* a);
 lval* builtin_join(lval* a);
 lval* lval_join(lval* x, lval* y);
+lval* builtin_cons(lval* a);
+lval* builtin_len(lval* a);
+lval* builtin_init(lval* a);