+ Can lex basic tokens.

+ Can parse basic syntax.
+ Can eval integer multiplication.

1 files changed, 60 insertions, 0 deletions

diff --git a/src/lang/lexer.clj b/src/lang/lexer.clj
new file mode 100644
index 000000000..191686cb8
--- /dev/null
+++ b/src/lang/lexer.clj
@@ -0,0 +1,60 @@
+(ns lang.lexer
+  (:require [clojure.core.match :refer [match]]
+            [lang.util :as &util :refer [exec return* return fail fail*
+                                         repeat-m try-m try-all-m]]))
+
+(declare lex-form)
+
+;; [Utils]
+(defn ^:private lex-regex [regex]
+  (fn [text]
+    (if-let [[match] (re-find regex text)]
+      (return* (.substring text (.length match)) match)
+      (fail* "Pattern failed."))))
+
+(defn ^:private lex-str [str]
+  (fn [text]
+    (if (.startsWith text str)
+      (return* (.substring text (.length str)) str)
+      (fail* "String failed."))))
+
+;; [Lexers]
+(def ^:private lex-white-space (lex-regex #"^(\s+)"))
+
+(def ^:private lex-list
+  (exec [_ (lex-str "(")
+         members (repeat-m lex-form)
+         _ (lex-str ")")]
+    (return [::list members])))
+
+(def ^:private lex-ident
+  (exec [token (lex-regex #"^([a-zA-Z!@$%^&*<>\.,/\\\|][a-zA-Z0-9!@$%^&*<>\.,/\\\|]*)")]
+    (return [::ident token])))
+
+(def ^:private lex-int
+  (exec [token (lex-regex #"^([1-9][0-9]*)")]
+    (return [::int token])))
+
+(def ^:private lex-form
+  (exec [_ (try-m lex-white-space)
+         form (try-all-m [lex-list
+                          lex-ident
+                          lex-int
+                          ])
+         _ (try-m lex-white-space)]
+    (return form)))
+
+;; [Interface]
+(defn lex [text]
+  (match ((exec [_ (try-m lex-white-space)
+                 form lex-list
+                 _ (try-m lex-white-space)]
+            (return form))
+          text)
+    [::&util/ok [?state ?datum]]
+    (if (empty? ?state)
+      ?datum
+      (assert false (str "Unconsumed input: " ?state)))
+    
+    [::&util/failure ?message]
+    (assert false ?message)))