tisp

commit 4dac1c2d761c9cfc5b801a0502d0a2e9b650ee72
parent bc31c9ccfb4840e72b849453f656c3abba24ba5d
Author: Ed van Bruggen <edvb@uw.edu>
Date:   Mon,  1 Jun 2020 01:26:15 -0700

Make symbol self evaluating if only arg to define

Diffstat:
doc/tisp.1.md
 | 
3
++-
tibs/doc.tsp
 | 
5
+++--
tisp.c
 | 
8
++++----

3 files changed, 9 insertions(+), 7 deletions(-)
diff --git a/doc/tisp.1.md b/doc/tisp.1.md
@@ -221,7 +221,8 @@ argument list and rest as macro's body.
 
 Create variable with the name of the first argument, with the value of the
 second. If name given is a list use the first element of this list as a new
-functions name and rest of list as its arguments.
+functions name and rest of list as its arguments. If only variable name is
+given make it self evaluating.
 
 #### set!
 
diff --git a/tibs/doc.tsp b/tibs/doc.tsp
@@ -36,9 +36,10 @@
       "(macro args . body)"
       "create anonymous macro")
     (define
-      "(define var val)"
+      "(define var . val)"
       "(define (func . args) . body)"
-      "creates new variable with value, or create new function if argument list given")
+      "creates new variable with value, or create new function if argument list given"
+      "if value for variable is not given, make it a self-evaluating symbol")
     (set!
       "(set! var val)"
       "change the variable var to val")
diff --git a/tisp.c b/tisp.c
@@ -990,7 +990,7 @@ static Val
 prim_define(Tsp st, Hash env, Val args)
 {
 	Val sym, val;
-	tsp_arg_min(args, "define", 2);
+	tsp_arg_min(args, "define", 1);
 	if (car(args)->t == PAIR) { /* create function if given argument list */
 		sym = caar(args); /* first element of argument list is function name */
 		if (sym->t != SYMBOL)
@@ -999,12 +999,12 @@ prim_define(Tsp st, Hash env, Val args)
 			          type_str(sym->t));
 		val = mk_func(FUNCTION, sym->v.s, cdar(args), cdr(args), env);
 	} else if (car(args)->t == SYMBOL) { /* create variable */
-		sym = car(args);
-		val = tisp_eval(st, env, cadr(args));
+		sym = car(args); /* if only symbol given, make it self evaluating */
+		val = nilp(cdr(args)) ? sym : tisp_eval(st, env, cadr(args));
 	} else tsp_warn("define: incorrect format, no variable name found");
 	if (!val)
 		return NULL;
-	/* set procedure name if it was previously anoymous */
+	/* set procedure name if it was previously anonymous */
 	if (val->t & (FUNCTION|MACRO) && !val->v.f.name)
 		val->v.f.name = sym->v.s;
 	hash_add(env, sym->v.s, val);