Implement arity checks

1 files changed, 24 insertions, 4 deletions

@@ -7,10 +7,30 @@ function m.pop (tbl)
         return table.remove(tbl, 1)
 end
 
-function m.arity (r, min, max)
-        --[[ Return whether R is within MIN and MAX (inclusive). ]]
-        local len = #r
-        return len >= min and len <= max
+function m.proc (arity, fn)
+        --[[ Wrap RN in a check that for its ARITY.
+                ARITY can be a number, the minimum number of arguments,
+                or a table {MIN, MAX}.  If MIN is nil or absent, it's 0;
+                if MAX is nil or absent, it's infinity.  MIN and MAX are
+                both inclusive.
+        ]]
+        local rmin, rmax, rstr
+        if type(arity) ~= "table" then
+                rmin, rmax = arity, arity
+                rstr = rmin
+        else
+                rmin, rmax = arity[1] or 0, arity[2] or 1/0 -- infinity
+                rstr = rmin .. ".." .. rmax
+        end
+        return function (r)
+                local rlen = r and #r or 0
+                if rlen < rmin or rlen > rmax then
+                        error(string.format("Wrong arity: %s, need %s",
+                                        rlen,
+                                        rstr))
+                end
+                return fn(r)
+        end
 end
 
 ---