tisp

commit 74059fd448ccc311417ceddf591a1825cffe3ecf
parent b6f853c5d4282f67a106d0e5ba90963f5525cad0
Author: Ed van Bruggen <edvb@uw.edu>
Date:   Sat, 14 Apr 2018 16:24:22 -0700

Add - primitive to subtract and negate integers

Diffstat:
tib/math.c
 | 
19
++++++++++++++++++-

1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/tib/math.c b/tib/math.c
@@ -23,8 +23,25 @@ prim_add(Hash env, Val args)
 	return mk_int(i);
 }
 
+static Val
+prim_sub(Hash env, Val args)
+{
+	Val v;
+	int i = 0;
+	if (!(v = eval_list(env, args)))
+		return NULL;
+	INC(+, "-");
+	v = cdr(v);
+	if (nilp(v))
+		return mk_int(-i);
+	for (; !nilp(v); v = cdr(v))
+		INC(-, "-");
+	return mk_int(i);
+}
+
 void
 tib_math_env(Hash ht)
 {
-	hash_add(ht, "+", mk_prim(prim_add));
+	hash_add(ht, "+",  mk_prim(prim_add));
+	hash_add(ht, "-",  mk_prim(prim_sub));
 }