From 6b00dfe1f51ddaa9f194d5649cbf6277682421bf Mon Sep 17 00:00:00 2001
From: Scott Richmond <kredati@users.noreply.github.com>
Date: Tue, 28 Dec 2021 18:24:42 -0500
Subject: [PATCH] Fiddle with the scanner.

---
 src/ludus/scanner.clj | 80 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 67 insertions(+), 13 deletions(-)

diff --git a/src/ludus/scanner.clj b/src/ludus/scanner.clj
index d5cc7a0..9e00e5e 100644
--- a/src/ludus/scanner.clj
+++ b/src/ludus/scanner.clj
@@ -14,12 +14,14 @@
     "false"
     "as"
     "ref"
-    "swap"
+    "swap"})
     ;; other possibilities
     ;; "pattern" -- first class patterns?
-    })
+    
 
-(defn- new-scanner [source]
+(defn- new-scanner 
+  "Creates a new scanner."
+  [source]
   {::source source
    ::length (count source)
    ::errors []
@@ -28,16 +30,29 @@
    ::line 1
    ::tokens []})
 
-(defn- at-end? [scanner]
+(defn- at-end? 
+  "Tests if a scanner is at end of input."
+  [scanner]
   (>= (::current scanner) (::length scanner)))
 
-(defn- current-char [scanner]
+(defn- current-char 
+  "Gets the current character of the scanner."
+  [scanner]
   (nth (::source scanner) (::current scanner)))
 
-(defn- advance [scanner]
+(defn- advance 
+  "Advances the scanner by a single character."
+  [scanner]
   (update scanner ::current inc))
 
-(defn- current-lexeme [scanner]
+(defn- next-char 
+  "Gets the next character from the scanner."
+  [scanner]
+  (current-char (advance scanner)))
+
+(defn- current-lexeme 
+  
+  [scanner]
   (subs (::source scanner) (::start scanner) (::current scanner)))
 
 (defn- char-in-range? [start end char]
@@ -58,8 +73,11 @@
 (defn- whitespace? [c]
   (or (= c \space) (= c \tab) (= c \return) (= c \,)))
 
+
+(def terminators #{\: \; \newline \{ \( \[ \$ \# \- \< \&})
+
 (defn- terminates? [c]
-  (or (whitespace? c) (= c \:) (= c \newline)))
+  (or (whitespace? c) (contains? terminators c)))
 
 (defn- add-token
   ([scanner token-type]
@@ -67,13 +85,32 @@
   ([scanner token-type literal]
    (update scanner ::tokens conj (token/token token-type (current-lexeme scanner) literal (::line scanner)))))
 
+(defn- add-error [scanner msg])
+
+(defn- scan-keyword 
+  ([scanner] (scan-keyword scanner scanner))
+  ([start current])
+  )
+
+(defn- add-keyword [scanner]
+  (let [advanced (advance scanner)
+        char (current-char advanced)]
+    (if (not (alpha? char))
+      (add-error scanner (str "Keywords must start with a letter, e.g. :foo. Got " \: char))
+     (scan-keyword advanced))))
+
 (defn- add-number [scanner])
 
 (defn- add-string [scanner])
 
+(defn- add-comment [scanner])
+
+(defn- add-word [scanner])
+
 (defn- scan-token [scanner]
   (let [char (current-char scanner)
-        scanner (advance scanner)]
+        scanner (advance scanner)
+        next (next-char scanner)]
     (case char
       ;; one-character tokens
       \( (add-token scanner ::token/lparen)
@@ -83,25 +120,42 @@
       \[ (add-token scanner ::token/lbracket)
       \] (add-token scanner ::token/rbracket)
       \; (add-token scanner ::token/semicolon)
+      \_ (add-token scanner ::token/placeholder)
       \newline (add-token scanner ::token/newline)
+
       ;; two-character tokens
       ;; ->
+      \- (if (= next \>)
+           (add-token (advance (advance scanner)) ::token/rarrow)
+           (add-error scanner (str "Expected ->. Got " char next)))
       ;; <-
-      ;; //
+      \< (if (= next \-)
+           (add-token (advance (advance scanner)) ::token/larrow)
+           (add-error scanner (str "Expected <-. Got " char next)))
+
       ;; begin hashmap #{
+      \# (if (= next \{)
+           (add-token (advance (advance scanner)) ::token/starthash)
+           (add-error scanner (str "Expected beginning of hash: #{. Got " char next)))
       ;; begin set ${
+      \$ (if (= next \{)
+           (add-token (advance (advance scanner)) ::token/startset)
+           (add-error scanner (str "Expected beginning of set: ${. Got " char next)))
+
+      ;; comments
+      ;; &
+      \& (add-comment scanner)
 
       ;; keywords
-      ;;\: (add-keyword scanner)
+      \: (add-keyword scanner)
 
       ;; strings
-      ;;\"
+      \" (add-string scanner)
 
       ;; word matches
       (comment (cond
                  (digit? char) (add-number scanner)
                  (alpha? char) (add-word scanner)
-                 (= \_ char) (add-placeholder scanner)
                  :else (add-error scanner (str "Unexpected character: " char)))))))
 
 (defn- next-token [scanner]