Issue #480 - Make (expand) easier to use

Only require a single expression argument. The remaining environment arguments are generally not required when debugging from the REPL. This makes expand much easier to use for casual debugging.

docs/api/scheme/eval.md

@@ -34,6 +34,11 @@ A non-standard function to initialize a new global environment.
 
 # expand
 
-    (expand expr environment rename-environment)
+    (expand expr [[environment] [rename-environment]])
+
+Perform macro expansion on `expr` and return the resulting expression.
+
+`environment` may be optionally passed as the current environment. 
+
+`rename-environment` is an optional argument of an environment containing variables renamed directly by macros. This would generally be an empty environment when using this function for macro debugging.
 
-Perform macro expansion on `expr` and `environment` is the current environment. `rename-environment` is an environment containing variables renamed directly by macros; this would generally be an empty environment when using this function for macro debugging.

scheme/eval.sld

@@ -982,8 +982,14 @@
 ;TODO: modify this whole section to use macros:get-env instead of *defined-macros*. macro:get-env becomes the mac-env. any new scopes need to extend that env, and an env parameter needs to be added to (expand). any macros defined with define-syntax use that env as their mac-env (how to store that)?
 ; expand : exp -> exp
 
-(define (expand exp env rename-env)
-  (_expand exp env rename-env '() '()))
+(define (expand exp . opts)
+  (let ((env (if (> (length opts) 0) 
+                 (car opts)
+                 *global-environment*))
+        (rename-env (if (> (length opts) 1) 
+                        (cadr opts) 
+                        (env:extend-environment '() '() '()))))
+    (_expand exp env rename-env '() '())))
 
 ;; Internal implementation of expand
 ;; exp - Expression to expand