Add ansi-string-length.

README.md

@@ -163,6 +163,13 @@ black text.
 
 Generic highlight of given text. Defaults to bold blue text.
 
+    (ansi-string-length str)
+
+* ```str``` string that may contain ANSI CSI SGR sequences
+
+Returns the string length in characters without any ANSI CSI SGR
+sequences contained.
+
 ### Command Line parsing
 
 Generic syntax-based implementation of command-line options parsing

ansi.scm

@@ -82,6 +82,31 @@
  (define a:muted (ansi #:black #:bold))
  (define a:highlight (ansi #:blue #:bold))
 
+ ;; Returns visual string length in characters skipping any ANSI CSI
+ ;; SGR sequences.
+ ;;
+ ;; Internal states:
+ ;; 0 - regular string
+ ;; 1 - seen escape
+ ;; 2 - CSI started
+ (define (ansi-string-length str)
+   (let loop ((lst (string->list str))
+	      (state 0)
+	      (len 0))
+     (if (null? lst)
+	 len
+	 (let ((ch (car lst)))
+	   (case state
+	     ((0) (if (eq? ch #\escape)
+		      (loop (cdr lst) 1 len)
+		      (loop (cdr lst) 0 (add1 len))))
+	     ((1) (if (eq? ch #\[)
+		      (loop (cdr lst) 2 len)
+		      (loop (cdr lst) 0 len)))
+	     ((2) (if (eq? ch #\m)
+		      (loop (cdr lst) 0 len)
+		      (loop (cdr lst) 2 len))))))))
+
  ;; Performs ANSI module self-tests.
  (define (ansi-tests!)
    (run-tests
@@ -89,6 +114,9 @@
     (test-equal? ansi (ansi #:red) "\x1b[31m")
     (test-equal? ansi (ansi #:nonsense) "")
     (test-equal? ansi (ansi #:default) "\x1b[0m")
+    (test-eq? ansi-string-length (ansi-string-length "test") 4)
+    (test-eq? ansi-string-length (ansi-string-length "\x1b[1mtest") 4)
+    (test-eq? ansi-string-length (ansi-string-length "\x1b[30mtest\x1b[0m") 4)
     ))
 
  )