Merge pull request #122 from shwestrick/reverb-example

New example: audio reverb effect on .wav files

examples/Makefile

@@ -11,7 +11,8 @@ PROGRAMS= \
 	tokens \
 	nn \
 	dedup \
-	nqueens
+	nqueens \
+	reverb
 
 all: $(PROGRAMS)
 

examples/README.md

@@ -108,3 +108,12 @@ $ make nn
 $ bin/nn @mpl procs 4 -- -N 10000 -output result.ppm -resolution 1000
 ```
 
+## Reverb
+
+Applies an artificial reverberation effect to a `.wav` sound file. At the
+moment, it only supports either 8-bit or 16-bit PCM, and if there
+are multiple channels, these will be mixed into a mono-channel output.
+```
+$ make reverb
+$ bin/reverb @mpl procs 4 -- INPUT.wav -output OUTPUT.wav
+```

examples/lib/CommandLineArgs.sml

@@ -2,14 +2,15 @@ structure CommandLineArgs :
 sig
   (* each takes a key K and a default value D, looks for -K V in the
    * command-line arguments, and returns V if it finds it, or D otherwise. *)
-  val parseString : string -> string -> string
-  val parseInt : string -> int -> int
-  val parseBool : string -> bool -> bool
+  val parseString: string -> string -> string
+  val parseInt: string -> int -> int
+  val parseReal: string -> real -> real
+  val parseBool: string -> bool -> bool
 
   (* parseFlag K returns true if --K given on command-line *)
-  val parseFlag : string -> bool
+  val parseFlag: string -> bool
 
-  val positional : unit -> string list
+  val positional: unit -> string list
 end =
 struct
 
@@ -20,7 +21,21 @@ struct
     )
 
   fun positional () =
-    List.filter (not o String.isPrefix "-") (CommandLine.arguments ())
+    let
+      fun loop found rest =
+        case rest of
+          [] => List.rev found
+        | [x] => List.rev (if not (String.isPrefix "-" x) then x::found else found)
+        | x::y::rest' =>
+            if not (String.isPrefix "-" x) then
+              loop (x::found) (y::rest')
+            else if String.isPrefix "--" x then
+              loop found (y::rest')
+            else
+              loop found rest'
+    in
+      loop [] (CommandLine.arguments ())
+    end
 
   fun search key args =
     case args of
@@ -45,6 +60,15 @@ struct
           NONE => die ("Cannot parse integer from \"-" ^ key ^ " " ^ s ^ "\"")
         | SOME x => x
 
+  fun parseReal key default =
+    case search ("-" ^ key) (CommandLine.arguments ()) of
+      NONE => default
+    | SOME [] => die ("Missing argument of \"-" ^ key ^ "\" ")
+    | SOME (s :: _) =>
+        case Real.fromString s of
+          NONE => die ("Cannot parse real from \"-" ^ key ^ " " ^ s ^ "\"")
+        | SOME x => x
+
   fun parseBool key default =
     case search ("-" ^ key) (CommandLine.arguments ()) of
       NONE => default