Add logic to open file, lex single character symbols, tests

1 files changed, 52 insertions, 0 deletions

diff --git a/src/lex.lisp b/src/lex.lisp
new file mode 100644
index 0000000..ad386ba
--- /dev/null
+++ b/src/lex.lisp
@@ -0,0 +1,52 @@
+(in-package #:lex)
+
+(defun file->tokens (file)
+  "Opens FILE and parses returns a list of tokens, or
+NIL if the file could not be opened."
+
+  (defun read-tokens (tokens-so-far)
+    "Collects tokens in FILE into TOKENS-SO-FAR."
+    (let ((token (read-token)))
+      (if token
+          (read-tokens (cons token tokens-so-far))
+          (reverse tokens-so-far))))
+
+  (and (probe-file file)
+       (with-open-file (*standard-input* file :direction :input)
+         (read-tokens '()))))
+
+(defun read-token ()
+  "Reads *STANDARD-INPUT* and returns a token, or nil if the end
+of file has been reached.
+Whitespace, commas, colons, and parentheses are token delimiters.
+Comments start with a semi-colon ';' and all tokens after are ignored."
+  (let ((chr (read-char *standard-input* nil)))
+    (cond
+      ((null chr) chr)
+      ((whitespace-char-p chr)
+       (read-token))
+
+      ((char= chr #\;)
+       (progn (read-line *standard-input* nil)
+              (read-token)))
+
+      ((char= chr #\() 'left-paren)
+      ((char= chr #\)) 'right-paren)
+
+      ((digit-char-p chr)
+       (read-immediate chr))
+
+      ((alpha-char-p chr)
+       (read-identifier chr))
+
+      (t (error (format nil "~a is not a valid lexical symbol.~%" chr))))))
+
+(defun read-immediate (chr)
+  'immediate)
+
+(defun read-identifier (chr)
+  'id)
+
+(defun whitespace-char-p (x)
+  (or (char= #\space x)
+      (not (graphic-char-p x))))