3 files changed, 19 insertions, 6 deletions

@@ -34,6 +34,8 @@ Other extras include
 - `(read-port)`, `(read-port port)` reads a port until hitting end-of-file (IDK
   why this isn't in R7RS!), in chunks of `read-port-chunk-size`
 - `(defined?  x)` returns whether the symbol `x` is bound to a variable
+- `(with-input-from-string str thunk)` calls `thunk` with `str` bound as the current-input-port.
+- `(with-output-to-string thunk)` calls `thunk` and returns a string of the output.
 - `(displayed x)`, `(->string x)` returns `x` as a string (via `display`)
 - `(written x)` returns `x` as a string (via `write`)
 - `(print x ...)` displays `x ...` followed by a newline
@@ -113,17 +113,26 @@
          (eval sym (interaction-environment))
          #t)))))
 
-(define (displayed x)
+(define (with-output-to-string thunk)
   (call-with-port (open-output-string)
     (lambda (port)
-      (display x port)
+      (parameterize ((current-output-port port))
+        (thunk))
       (get-output-string port))))
 
-(define (written x)
-  (call-with-port (open-output-string)
+(define (with-input-from-string s thunk)
+  (call-with-port (open-input-string s)
     (lambda (port)
-      (write x port)
-      (get-output-string port))))
+      (parameterize ((current-input-port port))
+        (thunk)))))
+
+(define (displayed x)
+  (with-output-to-string
+    (lambda () (display x))))
+
+(define (written x)
+  (with-output-to-string
+    (lambda () (write x))))
 
 (define (print . xs)
   (for-each display xs)
@@ -382,6 +382,8 @@
           read-port
           read-port-chunk-size
           defined?
+          with-output-to-string
+          with-input-from-string
           displayed ->string
           written
           print)