Still work to do in the manual...

src/ltn12.lua

@@ -23,6 +23,7 @@ BLOCKSIZE = 2048
 -----------------------------------------------------------------------------
 -- returns a high level filter that cycles a low-level filter
 function filter.cycle(low, ctx, extra)
+    assert(low)
     return function(chunk)
         local ret
         ret, ctx = low(ctx, chunk, extra)
@@ -32,6 +33,7 @@ end
 
 -- chains two filters together
 local function chain2(f1, f2)
+    assert(f1 and f2)
     local co = coroutine.create(function(chunk)
         while true do
             local filtered1 = f1(chunk)
@@ -95,6 +97,7 @@ end
 
 -- turns a fancy source into a simple source
 function source.simplify(src)
+    assert(src)
     return function()
         local chunk, err_or_new = src()
         src = err_or_new or src
@@ -118,6 +121,7 @@ end
 
 -- creates rewindable source
 function source.rewind(src)
+    assert(src)
     local t = {}
     return function(chunk)
         if not chunk then
@@ -132,6 +136,7 @@ end
 
 -- chains a source with a filter
 function source.chain(src, f)
+    assert(src and f)
     local co = coroutine.create(function()
         while true do 
             local chunk, err = src()
@@ -186,6 +191,7 @@ end
 
 -- turns a fancy sink into a simple sink
 function sink.simplify(snk)
+    assert(snk)
     return function(chunk, err)
         local ret, err_or_new = snk(chunk, err)
         if not ret then return nil, err_or_new end
@@ -224,6 +230,7 @@ end
 
 -- chains a sink with a filter 
 function sink.chain(f, snk)
+    assert(f and snk)
     return function(chunk, err)
         local filtered = f(chunk)
         local done = chunk and ""
@@ -248,6 +255,7 @@ end
 
 -- pumps all data from a source to a sink, using a step function
 function pump.all(src, snk, step)
+    assert(src and snk)
     step = step or pump.step
     while true do
         local ret, err = step(src, snk)