diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0ea16f10..57d013af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,11 +4,13 @@ All notable changes to this project will be documented in this file.
 ## 0.5.0 - ??
 - Remove `*env*`, and `*doc-width*`.
 - Add `fiber/getenv`, `fiber/setenv`, and `dyn`, and `setdyn`.
+- Add support for dynamic bindings (via the `dyn` and `setdyn` functions).
 - Change signatures of some functions like `eval` which no longer takes
   an optional environment.
 - Add printf function
 - Make `pp` configurable with dynamic binding `:pretty-format`.
 - Remove the `meta` function.
+- Add `with-dyns` for blocks with dynamic bindings assigned.
 
 ## 0.4.1 - 2019-04-14
 - Squash some bugs
diff --git a/src/boot/boot.janet b/src/boot/boot.janet
index 796b0219..130087d0 100644
--- a/src/boot/boot.janet
+++ b/src/boot/boot.janet
@@ -852,6 +852,19 @@
     (set prev ~(if-let [,sym ,prev] ,next-prev)))
   prev)
 
+(defmacro with-dyns
+  "Run a block of code in a new fiber that has some
+  dynamic bindings set. The fiber will not mask errors
+  or signals, but the dynamic bindings will be properly
+  unset, as dynamic bindings are fiber local."
+  [bindings & body]
+  (with-syms [currenv env fib]
+    ~(let [,currenv (,fiber/getenv (,fiber/current))
+           ,env (,table/setproto (,table ,;bindings) ,currenv)
+           ,fib (,fiber/new (fn [] ,;body) :)]
+       (,fiber/setenv ,fib ,env)
+       (,resume ,fib))))
+
 (defn partial
   "Partial function application."
   [f & more]
diff --git a/src/core/capi.c b/src/core/capi.c
index 845303f9..13482785 100644
--- a/src/core/capi.c
+++ b/src/core/capi.c
@@ -204,3 +204,18 @@ JanetRange janet_getslice(int32_t argc, const Janet *argv) {
     }
     return range;
 }
+
+Janet janet_dyn(const char *name) {
+    if (janet_vm_fiber->env) {
+        return janet_table_get(janet_vm_fiber->env, janet_ckeywordv(name));
+    } else {
+        return janet_wrap_nil();
+    }
+}
+
+void janet_setdyn(const char *name, Janet value) {
+    if (!janet_vm_fiber->env) {
+        janet_vm_fiber->env = janet_table(1);
+    }
+    janet_table_put(janet_vm_fiber->env, janet_ckeywordv(name), value);
+}
diff --git a/src/core/corelib.c b/src/core/corelib.c
index 78fc5ae5..1860cd6b 100644
--- a/src/core/corelib.c
+++ b/src/core/corelib.c
@@ -111,19 +111,6 @@ static Janet janet_core_native(int32_t argc, Janet *argv) {
     return janet_wrap_table(env);
 }
 
-static Janet janet_core_print(int32_t argc, Janet *argv) {
-    for (int32_t i = 0; i < argc; ++i) {
-        int32_t j, len;
-        const uint8_t *vstr = janet_to_string(argv[i]);
-        len = janet_string_length(vstr);
-        for (j = 0; j < len; ++j) {
-            putc(vstr[j], stdout);
-        }
-    }
-    putc('\n', stdout);
-    return janet_wrap_nil();
-}
-
 static Janet janet_core_describe(int32_t argc, Janet *argv) {
     JanetBuffer *b = janet_buffer(0);
     for (int32_t i = 0; i < argc; ++i)
@@ -296,13 +283,6 @@ static const JanetReg corelib_cfuns[] = {
              "Returns an environment table that contains functions and other values "
              "from the native module.")
     },
-    {
-        "print", janet_core_print,
-        JDOC("(print & xs)\n\n"
-             "Print values to the console (standard out). Value are converted "
-             "to strings if they are not already. After printing all values, a "
-             "newline character is printed. Returns nil.")
-    },
     {
         "describe", janet_core_describe,
         JDOC("(describe x)\n\n"
diff --git a/src/core/io.c b/src/core/io.c
index d582a372..bb95d79b 100644
--- a/src/core/io.c
+++ b/src/core/io.c
@@ -333,7 +333,37 @@ static Janet io_file_get(void *p, Janet key) {
     return janet_getmethod(janet_unwrap_keyword(key), io_file_methods);
 }
 
+static IOFile *io_isfile(Janet x) {
+    if (!janet_checktype(x, JANET_ABSTRACT)) return NULL;
+    void *abstract = janet_unwrap_abstract(x);
+    if (janet_abstract_type(abstract) != &cfun_io_filetype) return NULL;
+    return (IOFile *)abstract;
+}
+
+static Janet cfun_io_print(int32_t argc, Janet *argv) {
+    /* Get output stream */
+    IOFile *outf = io_isfile(janet_dyn("out"));
+    FILE *f = outf ? outf->file : stdout;
+    for (int32_t i = 0; i < argc; ++i) {
+        int32_t j, len;
+        const uint8_t *vstr = janet_to_string(argv[i]);
+        len = janet_string_length(vstr);
+        for (j = 0; j < len; ++j) {
+            putc(vstr[j], f);
+        }
+    }
+    putc('\n', f);
+    return janet_wrap_nil();
+}
+
 static const JanetReg io_cfuns[] = {
+    {
+        "print", cfun_io_print,
+        JDOC("(print & xs)\n\n"
+             "Print values to the console (standard out). Value are converted "
+             "to strings if they are not already. After printing all values, a "
+             "newline character is printed. Returns nil.")
+    },
     {
         "file/open", cfun_io_fopen,
         JDOC("(file/open path [,mode])\n\n"
diff --git a/src/include/janet.h b/src/include/janet.h
index 169dca0c..c3d427cf 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -1281,6 +1281,9 @@ JANET_API int32_t janet_getargindex(const Janet *argv, int32_t n, int32_t length
 
 JANET_API FILE *janet_getfile(const Janet *argv, int32_t n, int *flags);
 
+JANET_API Janet janet_dyn(const char *name);
+JANET_API void janet_setdyn(const char *name, Janet value);
+
 /* Marshal API */
 #define janet_marshal_size(ctx, x) janet_marshal_int64((ctx), (int64_t) (x))
 JANET_API void janet_marshal_int(JanetMarshalContext *ctx, int32_t value);