suggesting closest misspelled options (issue #588)

Makefile

@@ -47,11 +47,11 @@ BASE_INCLUDES = include/chibi/sexp.h include/chibi/features.h include/chibi/inst
 INCLUDES = $(BASE_INCLUDES) include/chibi/eval.h include/chibi/gc_heap.h
 
 MODULE_DOCS := app ast base64 bytevector config crypto/md5 crypto/rsa \
-	crypto/sha2 diff disasm doc equiv filesystem generic heap-stats io \
+	crypto/sha2 diff disasm doc edit-distance equiv filesystem generic \
-	iset/base iset/constructors iset/iterators loop match math/prime \
+	heap-stats io iset/base iset/constructors iset/iterators loop \
-	memoize mime modules net net/http-server net/servlet parse pathname \
+	match math/prime memoize mime modules net net/http-server net/servlet \
-	process repl scribble string stty sxml system temp-file test time \
+	parse pathname process repl scribble string stty sxml system temp-file \
-	trace type-inference uri weak monad/environment crypto/sha2
+	test time trace type-inference uri weak monad/environment crypto/sha2
 
 IMAGE_FILES = lib/chibi.img lib/red.img lib/snow.img
 
@@ -496,6 +496,7 @@ snowballs:
 	$(SNOW_CHIBI) package lib/chibi/crypto/rsa.sld
 	$(SNOW_CHIBI) package lib/chibi/crypto/sha2.sld
 	$(SNOW_CHIBI) package lib/chibi/diff.sld
+	$(SNOW_CHIBI) package lib/chibi/edit-distance.sld
 	$(SNOW_CHIBI) package lib/chibi/filesystem.sld
 	$(SNOW_CHIBI) package lib/chibi/math/prime.sld
 	$(SNOW_CHIBI) package lib/chibi/mime.sld

doc/chibi.scrbl

@@ -1303,6 +1303,8 @@ namespace.
 
 \item{\hyperlink["lib/chibi/doc.html"]{(chibi doc) - Chibi documentation utilities}}
 
+\item{\hyperlink["lib/chibi/edit-distance.html"]{(chibi edit-distance) - A levenshtein distance implementation}}
+
 \item{\hyperlink["lib/chibi/equiv.html"]{(chibi equiv) - A version of \scheme{equal?} which is guaranteed to terminate}}
 
 \item{\hyperlink["lib/chibi/filesystem.html"]{(chibi filesystem) - Interface to the filesystem and file descriptor objects}}

lib/chibi/app.scm

@@ -339,11 +339,30 @@
     (cond ((and (= 2 (length prefix))) '())
           ((null? prefix) '())
           (else (reverse (cdr (reverse  prefix))))))
+  (define (all-opt-names opt-spec)
+    ;; TODO: nested options
+    (let lp ((ls opt-spec) (res '()))
+      (if (null? ls)
+          (map (lambda (x) (if (symbol? x) (symbol->string x) x))
+               (remove char? (reverse res)))
+          (let ((o (car ls)))
+            (lp (cdr ls)
+                (append (if (and (pair? (cddr o)) (pair? (third o)))
+                            (third o)
+                            '())
+                        (cons (car o) res)))))))
   (let ((fail (if (pair? o)
                   (car o)
                   (lambda (prefix spec opt args reason)
-                    ;; TODO: search for closest option in "unknown" case
+                    (cond
-                    (error reason opt)))))
+                     ((and (string=? reason "unknown option")
+                           (find-nearest-edits opt (all-opt-names spec)))
+                      => (lambda (similar)
+                           (if (pair? similar)
+                               (error reason opt "Did you mean: " similar)
+                               (error reason opt))))
+                     (else
+                      (error reason opt)))))))
     (cond
      ((null? spec)
       (error "no procedure in application spec"))

lib/chibi/app.sld

@@ -9,5 +9,6 @@
           (scheme process-context)
           (srfi 1)
           (chibi config)
+          (chibi edit-distance)
           (chibi string))
   (include "app.scm"))

lib/chibi/edit-distance.sld

@@ -1,9 +1,15 @@
 
 (define-library (chibi edit-distance)
-  (export edit-distance)
+  (export edit-distance find-nearest-edits)
   (import (scheme base) (srfi 130))
   (begin
-    ;; levenshtein (quadratic time, linear memory)
+    ;;> Returns the levenshtein distance between s1 and s2 - a cost of
+    ;;> 1 per character insertion, deletion or update.  Runs in
+    ;;> quadratic time and linear memory.
+    ;;>
+    ;;> \example{(edit-distance "same" "same")}
+    ;;> \example{(edit-distance "same" "sand")}
+    ;;> \example{(edit-distance "Saturday" "Sunday")}
     (define (edit-distance s1 s2)
       (let* ((len1 (string-length s1))
              (len2 (string-length s2))
@@ -29,4 +35,18 @@
                                              (if (eqv? ch1 ch2) 0 1))))
                   (lp (+ j 1)
                       (string-cursor-next s1 sc1)
-                      old-diag))))))))))
+                      old-diag))))))))
+    ;;> Returns a list of strings in \var{str-ls} with the smallest
+    ;;> edit distance to \var{str}, preserving order.  If
+    ;;> \var{max-distance} is provided and positive, only return if
+    ;;> the edits are less or equal to that distance.
+    (define (find-nearest-edits str str-ls . o)
+      (let ((max-distance (if (pair? o) (car o) 1e100)))
+        (let lp ((ls str-ls) (dist (+ max-distance 1)) (res '()))
+          (if (null? ls)
+              (reverse res)
+              (let ((ed (edit-distance str (car ls))))
+                (cond
+                 ((= ed dist) (lp (cdr ls) dist (cons (car ls) res)))
+                 ((< ed dist) (lp (cdr ls) ed (list (car ls))))
+                 (else (lp (cdr ls) dist res))))))))))