avoid being O(n^2) in worst case, improve style

Author: simeonschaub

src/julia-parser.scm

@@ -2114,35 +2114,35 @@
 (define (unescape-parsed-string-literal strs)
   (map-at even? unescape-string strs))
 
+;; remove `\` followed by a newline
+(define (strip-escaped-newline s)
+  (let ((in  (open-input-string s))
+        (out (open-output-string)))
+    (define (loop preceding-backslash?)
+          (let ((c (read-char in)))
+            (cond ((eof-object? c))
+                  (preceding-backslash?
+                   (if (not (eqv? c #\newline))
+                       (begin (write-char #\\ out) (write-char c out)))
+                   (loop #f))
+                  ((eqv? c #\\) (loop #t))
+                  (else (write-char c out) (loop #f)))))
+    (loop #f)
+    (io.tostring! out)))
+
 (define (parse-string-literal s delim raw)
-  (let ((p (ts:port s)))
-    ((if raw identity unescape-parsed-string-literal)
-     (map (lambda (s)
-            (if (and (not raw) (string? s))
-                ;; remove `\` followed by a newline
-                (let ((spl (string-split s "\\\n")))
-                  (foldl (lambda (line s)
-                           ;; if there is an odd number of backslashes before the backslash
-                           ;; preceding the newline, keep the backslash and newline since
-                           ;; the backslash is actually escaped
-                           (define (odd-backslashes? (i (length s)))
-                             (and (> i 0)
-                                  (let ((i (string.dec s i)))
-                                    (and (eqv? (string.char s i) #\\)
-                                         (not (odd-backslashes? i))))))
-                           (if (odd-backslashes?)
-                               (string s "\\\n" line)
-                               (string s line)))
-                         ""
-                         spl))
-                s))
-          (if (eqv? (peek-char p) delim)
-              (if (eqv? (peek-char (take-char p)) delim)
-                  (map-first strip-leading-newline
-                             (dedent-triplequoted-string
-                               (parse-string-literal- 2 (take-char p) s delim raw)))
-                  (list ""))
-              (parse-string-literal- 0 p s delim raw))))))
+  (let* ((p (ts:port s))
+         (str (if (eqv? (peek-char p) delim)
+                  (if (eqv? (peek-char (take-char p)) delim)
+                      (map-first strip-leading-newline
+                                 (dedent-triplequoted-string
+                                   (parse-string-literal- 2 (take-char p) s delim raw)))
+                      (list ""))
+                  (parse-string-literal- 0 p s delim raw))))
+    (if raw str (unescape-parsed-string-literal
+                  (map (lambda (s)
+                         (if (string? s) (strip-escaped-newline s) s))
+                       str)))))
 
 (define (strip-leading-newline s)
   (let ((n (sizeof s)))