prompt: added emacs-like shortcuts

README.md

@@ -17,8 +17,6 @@ We support all builtin functions, but have no IO (no `print`).
 
 ## TODO
 
-- A good readline copy (haskeline is sadly out of the question for this project)
-  - Add keyboard shortcuts
 - Comment parsing
 - Closures that can modify the parent environment (but do away with the `local` keyword).
 - Better arbitrary precision floats

src/BC/Prompt.hs

@@ -212,15 +212,23 @@ readline state = read' "" 0
                   putStr [c]
                   read' (take pos acc ++ [c] ++ drop pos acc) (pos+1) pstate
                 else
-                  if ord c == 18 -- 18 == Ctrl+R
-                    then do
+                  case ord c of
+                    1  -> -- == cursor to beginning
+                      read' acc 0 pstate
+                    2  -> -- == cursor left
+                      read' acc (if pos > 0 then pos-1 else pos) pstate
+                    5  -> -- == cursor to end
+                      read' acc (length acc) pstate
+                    6  -> -- == cursor right
+                      read' acc (if pos < length acc then pos+1 else pos) pstate
+                    18 -> do -- == Ctrl+R
                        mnacc <- reverseSearch pstate acc
                        case mnacc of
                         Just nacc -> do
                           putStr nacc
                           return (Just nacc)
                         _         -> read' acc pos pstate
-                    else read' acc pos pstate
+                    _  ->read' acc pos pstate
         clamp n min max
             | n < min = min
             | n > max = max