[Ongoing] Rewrite frontend to use Flex/Bison

This is a merge of another experiment, so the changes are large:

- separated "modules" directory into frontend/backend
  - adjusted module names and moved files for this to happen
- removed modules lexer & parser
- removed all the unit tests (most were outdated)
- added Bison, flex, and C development tools to manifest.scm
- added lexer.l, a source file used by the flex utility with a functioning lexing implementation
- added parser.y, a source file used by the bison utility with a functioning parser implementation
- added node.c and node.h, which parser.y uses to construct an AST of a C source file (up to binary ops)
- added driver.c, a Guile-C interface that provides a module to scheme programs
- added a Makefile to make all of this
- added stuff to .gitignore

1 files changed, 0 insertions, 83 deletions

diff --git a/src/modules/lexer/driver.scm b/src/modules/lexer/driver.scm
deleted file mode 100644
index 92c8687..0000000
--- a/src/modules/lexer/driver.scm
+++ /dev/null
@@ -1,83 +0,0 @@
-(define-module (lexer driver)
-  #:export (read-tokens))
-
-(define (read-tokens)
-  "Returns a stream of tokens from the
-current input port."
-  (define (read-tokens-loop tokens-so-far)
-    (let ((token (read-token)))
-      (if token
-          (read-tokens-loop (cons token tokens-so-far))
-          (reverse tokens-so-far))))
-  (read-tokens-loop '()))
-
-(define (read-token)
-  (let ((chr (read-char)))
-    (cond
-     ((eof-object? chr) #f)
-     ((char-whitespace? chr)
-      (read-token))
-
-      ((eqv? chr #\() 'left-paren)
-      ((eqv? chr #\)) 'right-paren)
-      ((eqv? chr #\{) 'open-brace)
-      ((eqv? chr #\}) 'close-brace)
-      ((eqv? chr #\;) 'semi-colon)
-      ((eqv? chr #\~) 'not)
-      ((eqv? chr #\*) 'mul)
-      ((eqv? chr #\/) 'div)
-      ((eqv? chr #\%) 'mod)
-
-      ((eqv? chr #\+)
-       (if (take-double? chr)
-           '++
-           'add))
-
-      ((eqv? chr #\-)
-       (if (take-double? chr)
-           '--
-           'neg))
-
-      ((char-numeric? chr)
-       (read-constant chr))
-
-      ((char-alphabetic? chr)
-       (lookup-keyword (read-identifier chr)))
-
-      (#t (error "illegal lexical syntax")))))
-
-(define (read-constant chr)
-  (define (read-constant-helper chrs-so-far)
-    (let ((chr (peek-char)))
-      (cond ((and (not (eof-object? chr)) (char-numeric? chr))
-             (read-constant-helper (cons (read-char) chrs-so-far)))
-            ((and (not (eof-object? chr)) (char-alphabetic? chr))
-             (error "identifier starting with digit"))
-            (#t (reverse chrs-so-far)))))
-  (string->number (list->string (read-constant-helper (list chr)))))
-
-(define (read-identifier chr)
-  (define (read-identifier-helper chrs-so-far)
-    (let ((chr (peek-char)))
-      (cond ((and (not (eof-object? chr))
-              (or (char-alphabetic? chr)
-                  (char-numeric? chr)
-                  (eqv? chr #\_)))
-             (read-identifier-helper (cons (read-char) chrs-so-far)))
-            (#t (reverse chrs-so-far)))))
-  (list->string (read-identifier-helper (list chr))))
-
-(define (take-double? chr)
-  (if (eqv? chr (peek-char))
-      (read-char)
-      #f))
-
-(define (lookup-keyword id)
-  "Given identifier ID, converts it to a keyword
-if one is known."
-  (let ((found (assoc
-                id
-                '(("int" . int)
-                  ("void" . void)
-                  ("return" . return)))))
-    (if found (cdr found) id)))