1st attempt to implement head & tail functions

chapter_10/lispy.c

@@ -170,7 +170,7 @@ lval* lval_read(mpc_ast_t* t) {
 
     /* Fill this list with any valid expression
        contained within */
-    for (size_t i = 0; i < t->children_num; i++) {
+    for (size_t i = 0; i < (size_t) t->children_num; i++) {
         if (strcmp(t->children[i]->contents, "(") == 0) {
             continue;
         }
@@ -415,6 +415,66 @@ lval* builtin_op(lval* a, char* op) {
 }
 
 
+lval* builtin_head(lval* a) {
+
+    /* Check error conditions */
+    if (a->count != 1) {
+        lval_del(a);
+        return lval_err("Function 'head' passed too many arguments");
+    }
+
+    if (a->cell[0]->type != LVAL_QEXPR) {
+        lval_del(a);
+        return lval_err("Function 'head' passed incorrect types!");
+    }
+
+    if (a->cell[0]->count == 0) {
+        lval_del(a);
+        return lval_err("Function 'head' passed empty {}!");
+    }
+
+    /* Otherwise take first argument */
+    lval* v = lval_take(a, 0);
+
+    /* Delete all elements that are not head and return */
+    while (v-> count > 1) {
+        lval_del(lval_pop(v, 1));
+    }
+
+    return v;
+
+}
+
+
+lval* builtin_tail(lval* a) {
+
+    /* Check error conditions */
+    if (a->count != 1) {
+        lval_del(a);
+        return lval_err("Function 'tail' passed too many arguments");
+    }
+
+    if (a->cell[0]->type != LVAL_QEXPR) {
+        lval_del(a);
+        return lval_err("Function 'tail' passed incorrect types!");
+    }
+
+    if (a->cell[0]->count == 0) {
+        lval_del(a);
+        return lval_err("Function 'tail' passed empty {}!");
+    }
+
+    /* Otherwise take first argument */
+    lval* v = lval_take(a, 0);
+
+    /* Delete first element and return */
+    lval_del(lval_pop(v, 0));
+
+    return v;
+
+}
+
+
 long min(long x, long y) {
     if (x <= y) {
         return x;
@@ -433,7 +493,7 @@ long max(long x, long y) {
 }
 
 
-int main(int argc, char const *argv[]) {
+int main() {
 
     /* Create some parsers */
     mpc_parser_t* Number = mpc_new("number");
@@ -477,7 +537,7 @@ int main(int argc, char const *argv[]) {
     }
 
     /* Undefine and delete our parsers */
-    mpc_cleanup(5, Number, Symbol, Sexpr, Qexpr, Expr, Lispy);
+    mpc_cleanup(6, Number, Symbol, Sexpr, Qexpr, Expr, Lispy);
 
     return 0;
 }

chapter_10/lispy.h

@@ -3,22 +3,27 @@ static char* lispy_version = "Lispy version 0.0.0.0.6";
 
 /* Parser language defintion */
 static char* parser =
-"                                                        \
-    number   : /-?[0-9]+([.][0-9]*|[0-9]*)/ ;            \
-    symbol : '+' | '-' | '*' | '/' | '%' | '^' |         \
-    \"min\" | \"max\" ;                                  \
-    sexpr    : '(' <expr>* ')' ;                         \
-    qexpr    : '{' <expr>* '}' ;                         \
-    expr     : <number> | <symbol> | <sexpr> | <qexpr>;  \
-    lispy    : /^/ <expr>* /$/ ;                         \
+"                                                         \
+    number   : /-?[0-9]+([.][0-9]*|[0-9]*)/ ;             \
+    symbol : \"list\" | \"head\" | \"tail\" | \"join\" |  \
+             \"eval\" | '+' | '-' | '*' | '/' | '%' |     \
+             '^' | \"min\" | \"max\" ;                    \
+    sexpr    : '(' <expr>* ')' ;                          \
+    qexpr    : '{' <expr>* '}' ;                          \
+    expr     : <number> | <symbol> | <sexpr> | <qexpr>;   \
+    lispy    : /^/ <expr>* /$/ ;                          \
 ";
 
 
 /* Declare new lval struct */
 typedef struct lval {
     int type;
-    long num;
-    double dec;
+    /* only one of the two number/decimal is valid in a
+       lval instance, so we can use an anonymous union */
+    union {
+        long num;
+        double dec;
+    };
     /* Error & symbol types have some string data */
     char* err;
     char* sym;
@@ -29,7 +34,8 @@ typedef struct lval {
 
 
 /* Create enumeration of possible lval types */
-enum {LVAL_NUM, LVAL_DEC, LVAL_SYM, LVAL_SEXPR, LVAL_QEXPR, LVAL_ERR};
+enum lval_types {LVAL_NUM, LVAL_DEC, LVAL_SYM, LVAL_SEXPR,
+                 LVAL_QEXPR, LVAL_ERR};
 
 /* lval constructor functions */
 lval* lval_num(long x);
@@ -52,11 +58,14 @@ lval* lval_read(mpc_ast_t* t);
 lval* lval_eval_sexpr(lval* v);
 lval* lval_eval(lval* v);
 
+/* lval print functions */
 void lval_expr_print(lval* v, char open, char close);
 void lval_print(lval* v);
 void lval_println(lval* v);
 
+/* language built-in operators and functions */
 long min(long x, long y);
 long max(long x, long y);
-
 lval* builtin_op(lval* a, char* op);
+lval* builtin_head(lval* a);
+lval* builtin_tail(lval* a);