1 files changed, 127 insertions, 0 deletions
diff --git a/module/c/lex.scm b/module/c/lex.scm
new file mode 100644
index 00000000..322e20ed
--- /dev/null
+++ b/module/c/lex.scm
@@ -0,0 +1,127 @@
+(define-module (c lex)
+  :use-module (ice-9 peg)
+  :use-module (c operators)
+  :export (lex))
+
+
+;; Like the regular define-peg-pattern. But evaluates the
+;; pattern before treating it as a peg rule.
+(define-macro (define-define-peg-pattern name capture expr)
+  `(define-peg-pattern ,name ,capture
+     ;; NOTE how does this work if we are in a different module?
+     ;; It currently however isn't a problem since we don't export
+     ;; this macro.
+     ,(eval expr (current-module))))
+
+
+
+(define-peg-pattern base-8-digit body
+  (range #\0 #\7))
+
+(define-peg-pattern base-10-digit body
+  (range #\0 #\9))
+
+(define-peg-pattern base-16-digit body
+  (or (range #\0 #\9)
+      (range #\A #\F)
+      (range #\a #\f)))
+
+;; https://en.cppreference.com/w/cpp/language/integer_literal
+(define-peg-pattern base-10 all (+ base-10-digit))
+(define-peg-pattern base-8 all (and (ignore "0") (+ base-8-digit)))
+(define-peg-pattern base-16 all (and (ignore (and "0" (or "x" "X")))
+                                     (+ base-16-digit)))
+
+;; accept anything now, ensure correctnes later
+(define-peg-pattern integer-suffix all
+  (* (or "u" "U" "l" "L")))
+
+(define-peg-pattern integer all
+  (and (or base-8 base-16 base-10) (? integer-suffix)))
+
+(define-peg-pattern number body
+  (or integer))
+
+(define-peg-pattern group all
+  (and (ignore "(") expr (ignore ")")))
+
+(define-peg-pattern base-8-char all
+  (and base-8-digit
+       (? base-8-digit)
+       (? base-8-digit)))
+
+(define-peg-pattern base-16-char all
+  (and (ignore "x") base-16-digit (? base-16-digit)))
+
+(define-peg-pattern escaped-char all
+  (and (ignore "\\") (or base-16-char
+                         base-8-char
+                         peg-any)))
+
+(define-peg-pattern char all
+  (and (ignore "'") (or escaped-char peg-any) (ignore "'")))
+
+(define-define-peg-pattern operator all
+  `(or ,@(map symbol->string symbol-binary-operators)
+       ,@(map (lambda (op) `(and ,(symbol->string op) ws))
+              wordy-binary-operators)))
+
+;; whitespace
+(define-peg-pattern ws none
+  (or " " "	" "\n"))
+
+;; space (for when whitespace is optional)
+(define-peg-pattern sp none (* ws))
+
+(define-peg-pattern safe-letter body
+  (or "_"
+      (range #\A #\Z)
+      (range #\a #\z)))
+
+(define-peg-pattern variable all
+  (and safe-letter
+       (* (or safe-letter
+              base-10-digit))))
+
+;; No further subparsing can be done.
+;; NOTE that strings are generally also in this category.
+(define-peg-pattern atom all
+  (or base-8 base-10 base-16 number char variable))
+
+(define-peg-pattern prefix-operator all
+  (or "!" "~" "*" "&" "++" "--" "+" "-"))
+
+;;; Note that stacked pre or postfix operators without parenthesis
+;;; dosen't work. So `*&C' is invalid, while `*(&C)' is valid.
+
+(define-peg-pattern prefix all
+  (and prefix-operator sp (or variable group funcall #; postfix
+                              )))
+
+(define-peg-pattern postfix-operator all
+  (or "++" "--"))
+
+(define-peg-pattern postfix all
+  ;; literals can't be in-place incremented and decremented
+  ;; Make sure we don't match postfix-operator here, since
+  ;; that also gives us an infinite loop.
+  (and (or prefix funcall group variable) sp postfix-operator))
+
+(define-peg-pattern infix all
+  ;; first case is "same" as expr, but in different order to prevent
+  ;; infinite self reference. Pre and postfix not here, solved by having
+  ;; them before infix in expr
+  (and (or funcall postfix prefix group char number variable)
+       sp operator sp expr))
+
+(define-peg-pattern funcall all
+  (and variable sp group))
+
+;;; main parser
+(define-peg-pattern expr body
+  (+ (and sp (or infix postfix prefix funcall group char number variable)
+          sp)))
+
+
+(define (lex string)
+  (peg:tree (match-pattern expr string)))