Implement step 3

diff --git a/elisp/env.el b/elisp/env.el
new file mode 100644 (file)
index 0000000..c59d0c8
--- /dev/null
+++ b/elisp/env.el
@@ -0,0 +1,21 @@
+(defun mal-env (&optional outer)
+  (vector 'env (vector (make-hash-table :test 'eq) outer)))
+
+(defun mal-env-set (env key value)
+  (let ((data (aref (aref env 1) 0)))
+    (puthash key value data)))
+
+(defun mal-env-find (env key)
+  (let* ((data (aref (aref env 1) 0))
+         (value (gethash key data)))
+    (if (not value)
+        (let ((outer (aref (aref env 1) 1)))
+          (when outer
+            (mal-env-find outer key)))
+      value)))
+
+(defun mal-env-get (env key)
+  (let ((value (mal-env-find env key)))
+    (if (not value)
+        (error "%s not found" key)
+      value)))

diff --git a/elisp/step3_env.el b/elisp/step3_env.el
new file mode 100644 (file)
index 0000000..8dbbb09
--- /dev/null
+++ b/elisp/step3_env.el
@@ -0,0 +1,112 @@
+(defun load-relative (file)
+  (let* ((current-file (or load-file-name buffer-file-name))
+         (current-file-directory (file-name-directory current-file)))
+    (load (expand-file-name file current-file-directory) nil t)))
+
+(load-relative "types.el")
+(load-relative "env.el")
+(load-relative "reader.el")
+(load-relative "printer.el")
+
+(defvar repl-env (mal-env))
+(mal-env-set repl-env '+ (lambda (a b) (mal-number (+ (mal-value a) (mal-value b)))))
+(mal-env-set repl-env '- (lambda (a b) (mal-number (- (mal-value a) (mal-value b)))))
+(mal-env-set repl-env '* (lambda (a b) (mal-number (* (mal-value a) (mal-value b)))))
+(mal-env-set repl-env '/ (lambda (a b) (mal-number (/ (mal-value a) (mal-value b)))))
+
+(defun READ (input)
+  (read-str input))
+
+(defun EVAL (ast env)
+  (if (mal-list-p ast)
+      (let* ((a (mal-value ast))
+             (a0 (car a))
+             (a0* (mal-value a0))
+             (a1 (cadr a))
+             (a1* (mal-value a1))
+             (a2 (nth 2 a)))
+        (cond
+         ((eq a0* 'def!)
+          (let ((identifier a1*)
+                (value (EVAL a2 env)))
+            (mal-env-set env identifier value)))
+         ((eq a0* 'let*)
+          (let ((env* (mal-env env))
+                (bindings (if (vectorp a1*) (append a1* nil) a1*))
+                (form a2))
+            (while bindings
+              (let ((key (mal-value (pop bindings)))
+                    (value (EVAL (pop bindings) env*)))
+                (mal-env-set env* key value)))
+            (EVAL form env*)))
+         (t
+          ;; not a special form
+          (let* ((ast* (mal-value (eval-ast ast env)))
+                 (fn (car ast*))
+                 (args (cdr ast*)))
+            (apply fn args)))))
+    (eval-ast ast env)))
+
+(defun eval-ast (ast env)
+  (let ((type (mal-type ast))
+        (value (mal-value ast)))
+    (cond
+     ((eq type 'symbol)
+      (let ((definition (mal-env-get env value)))
+        (or definition (error "Definition not found"))))
+     ((eq type 'list)
+      (mal-list (mapcar (lambda (item) (EVAL item env)) value)))
+     ((eq type 'vector)
+      (mal-vector (vconcat (mapcar (lambda (item) (EVAL item env)) value))))
+     ((eq type 'map)
+      (let ((map (copy-hash-table value)))
+        (maphash (lambda (key value)
+                   (puthash key (EVAL value env) map))
+                 map)
+        (mal-map map)))
+     (t
+      ;; return as is
+      ast))))
+
+(defun PRINT (input)
+  (pr-str input t))
+
+(defun rep (input)
+  (PRINT (EVAL (READ input) repl-env)))
+
+(defun readln (prompt)
+  ;; C-d throws an error
+  (ignore-errors (read-from-minibuffer prompt)))
+
+(defun println (format-string &rest args)
+  (if (not args)
+      (princ format-string)
+    (princ (apply 'format format-string args)))
+  (terpri))
+
+(defun main ()
+  (let (eof)
+    (while (not eof)
+      (let ((input (readln "user> ")))
+        (if input
+            (condition-case err
+                (println (rep input))
+              (end-of-token-stream
+               ;; empty input, carry on
+               )
+              (unterminated-sequence
+               (let* ((type (cadr err))
+                      (end
+                       (cond
+                        ((eq type 'string) ?\")
+                        ((eq type 'list) ?\))
+                        ((eq type 'vector) ?\])
+                        ((eq type 'map) ?}))))
+                 (princ (format "Expected '%c', got EOF\n" end))))
+              (error ; catch-all
+               (println (error-message-string err))))
+          (setq eof t)
+          ;; print final newline
+          (terpri))))))
+
+(main)