Add REPL utility vars (#171)

* Add REPL utility vars

* Fix a typechecking error

* Silence linter

Author: chrisrink10

basilisp/cli.py

@@ -1,3 +1,4 @@
+import importlib
 # noinspection PyUnresolvedReferences
 import readline  # noqa: F401
 import traceback
@@ -7,8 +8,10 @@
 
 import basilisp.compiler as compiler
 import basilisp.lang.runtime as runtime
+import basilisp.lang.symbol as sym
 import basilisp.main as basilisp
 import basilisp.reader as reader
+from basilisp.util import Maybe
 
 
 @click.group()
@@ -33,10 +36,27 @@ def eval_str(s: str, ctx: compiler.CompilerContext, module: types.ModuleType):
     return last
 
 
+def bootstrap_repl(which_ns: str) -> types.ModuleType:
+    """Bootstrap the REPL with a few useful vars and returned the
+    bootstrapped module so it's functions can be used by the REPL
+    command."""
+    repl_ns = runtime.Namespace.get_or_create(sym.symbol('basilisp.repl'))
+    ns = runtime.Namespace.get_or_create(sym.symbol(which_ns))
+    repl_module = importlib.import_module('basilisp.repl')
+    ns.add_alias(sym.symbol('basilisp.repl'), repl_ns)
+    for name in ['*1', '*2', '*3', '*e', 'doc', 'pydoc', 'source']:
+        ns.intern(sym.symbol(name),
+                  Maybe(runtime.Var.find(sym.symbol(name, ns='basilisp.repl'))).or_else_raise(
+                      lambda: runtime.RuntimeException(
+                          f"Var basilisp.repl/{name} not found!")))  # pylint: disable=cell-var-from-loop
+    return repl_module
+
+
 @cli.command(short_help='start the Basilisp REPL')
 @click.option('--default-ns', default=runtime._REPL_DEFAULT_NS, help='default namespace to use for the REPL')
 def repl(default_ns):
     basilisp.init()
+    repl_module = bootstrap_repl(default_ns)
     ctx = compiler.CompilerContext()
     ns_var = runtime.set_current_ns(default_ns)
     while True:
@@ -53,16 +73,21 @@ def repl(default_ns):
             continue
 
         try:
-            print(compiler.lrepr(eval_str(lsrc, ctx, ns.module)))
+            result = eval_str(lsrc, ctx, ns.module)
+            print(compiler.lrepr(result))
+            repl_module.mark_repl_result(result)
         except reader.SyntaxError as e:
             traceback.print_exception(reader.SyntaxError, e, e.__traceback__)
+            repl_module.mark_exception(e)
             continue
         except compiler.CompilerException as e:
             traceback.print_exception(compiler.CompilerException, e,
                                       e.__traceback__)
+            repl_module.mark_exception(e)
             continue
         except Exception as e:
             traceback.print_exception(Exception, e, e.__traceback__)
+            repl_module.mark_exception(e)
             continue
 
 

basilisp/repl.lpy

@@ -0,0 +1,49 @@
+(in-ns 'basilisp.repl)
+
+(import* inspect)
+
+(def ^:dynamic *1 nil)
+(def ^:dynamic *2 nil)
+(def ^:dynamic *3 nil)
+(def ^:dynamic *e nil)
+
+(defn mark-repl-result
+  "Mark the REPL result and move each result to the next slot
+  down."
+  [result]
+  (set! '*3 *2)
+  (set! '*2 *1)
+  (set! '*1 result))
+
+(defn mark-exception
+  "Set the variable *e to the last exception at the REPL."
+  [e]
+  (set! '*e e))
+
+(defn pydoc
+  "Print the Python docstring for a function."
+  [o]
+  (print (inspect/getdoc o)))
+
+(defn print-doc
+  "Print the docstring from an interned var."
+  [v]
+  (let [var-meta (meta v)]
+    (if var-meta
+      (print (:doc var-meta))
+      nil)))
+
+(defmacro doc
+  "Print the docstring from an interned Var if found."
+  [s]
+  `(print-doc (var ~s)))
+
+(defn print-source
+  "Print the source forms for a function."
+  [v]
+  (throw (builtins/NotImplementedError)))
+
+(defmacro source
+  "Print the source code for a form if found."
+  [s]
+  `(print-source (var ~s)))