parse juxtapositions involving string literals as calls to string()

examples:
  "" x ""  =>  string(x)
  1+2 " equals " 3
  "" x y z ""

only happens in non-space-sensitive contexts, so macro calls and hcat
are not affected. empty string literals are removed.

Author: JeffBezanson

src/julia-parser.scm

@@ -419,13 +419,22 @@
 		    (if (not (eq? (take-token s) ':))
 			(error "colon expected in ? expression")
 			(list 'if ex then (parse-cond s))))))
-	  #;((string? ex)
-	   (let loop ((args (list ex)))
+	  ((and (or (string? ex) (eqv? (peek-token s) #\"))
+		(not space-sensitive))
+	   (let parse-strcat ((args (list ex)))
 	     (let ((next (peek-token s)))
-	       (if (or (eof-object? next) (closing-token? next)
-		       (newline? next))
-		   `(call (top string) ,@(reverse args))
-		   (loop (cons (parse-or s) args))))))
+	       (if (or (closing-token? next)
+		       (and (not range-colon-enabled)
+			    (eq? next ':))
+		       (and (not whitespace-newline)
+			    (newline? next)))
+		   (if (length= args 1)
+		       (car args)
+		       `(call (top string)
+			      ,@(reverse (filter (lambda (x)
+						   (not (equal? x "")))
+						 args))))
+		   (parse-strcat (cons (parse-or s) args))))))
 	  (else ex))))
 
 (define (invalid-initial-token? tok)
@@ -640,6 +649,8 @@
        (not (memq t reserved-words))
        (not (closing-token? t))
        (not (newline? t))
+       (not (string? expr))
+       (not (eqv? t #\"))
        (or (number? expr)
 	   (not (memv t '(#\( #\[ #\{))))))