merge soc07 r5069 - nselib for functional programming style 'list' operations

nselib/listopt.lua

@@ -0,0 +1,133 @@
+module('listopt', package.seeall)
+
+--[[
+--
+Functional programming style 'list' operations
+
+	bool	is_empty(list)
+	bool	is_list(value)
+
+	value	apply(function, list)
+	list	map(function, list)
+	list	filter(function, list)
+	list	flatten(list)
+	list	append(list1, list2)
+	list	cons(value1, value2)
+	list	reverse(list)
+
+	value	car(list)
+	value	ncar(list, x)
+	list	cdr(list)
+	list	ncdr(list, x)
+	
+	where 'list' is an indexed table 
+	where 'value' is an lua datatype
+--]]
+
+-- true if l is empty
+function is_empty(l)
+	return table.getn(l) == 0 and true or false
+end
+
+-- true if l is a list
+function is_list(l)
+	return type(l) == 'table' and true or false
+end
+
+-- Pass each elements of l to a function f which takes a single
+-- argument. All the results are returned in an list
+function map(f, l) 
+	local results = {}
+	for i, v in ipairs(l) do
+		table.insert(results, f(v))
+	end
+	return results
+end
+
+-- Pass all elements of l to function f which takes a variable 
+-- number of arguments or a number of arguments equal to the
+-- size of l. The result of f is returned
+function apply(f, l)
+	return f(unpack(l))
+end
+
+-- Pass all elements of l to a predicate function f which takes a single
+-- argument. All elements where f(l[x]) is true are returned in an 
+-- indexed list
+function filter(f, l) 
+	local results = {}
+	for i, v in ipairs(l) do
+		if(f(v)) then
+			table.insert(results, v)
+		end
+	end
+	return results
+end
+
+-- return first element of a list
+function car(l)
+	return l[1]
+end
+
+-- return everything but the first element of a list
+function cdr(l)
+	return ncdr(l)
+end
+
+-- same as car but start at element x
+function ncar(l, x)
+	x = x or 1
+	return l[x]
+end
+
+-- same as cdr but start at element x
+function ncdr(l, x) 
+	local results = {}
+	x = x or 2
+	for i = x, table.getn(l) do
+		results[i-1] = l[i]
+	end
+	return results
+end
+
+-- prepend a value or list to another value or list
+function cons(v1, v2)
+	return{ is_list(v1) and {unpack(v1)} or v1, is_list(v2) and {unpack(v2)} or v2}
+end
+
+-- concatenate two lists and return the result
+function append(l1, l2)
+	local results = {}
+	for i, v in ipairs(l1) do 
+		table.insert(results, v)
+	end
+
+	for i, v in ipairs(l2) do
+		table.insert(results, v)
+	end
+	return results
+end
+
+-- returned l in reverse order
+function reverse(l)
+	local results = {}
+	for i=table.getn(l), 1, -1 do
+		table.insert(results, l[i])
+	end
+	return results
+end
+
+-- return a flat version of nested list l
+function flatten(l)
+	local function flat(r, t)
+		for i, v in ipairs(t) do
+			if(type(v) == 'table') then
+				flat(r, v)
+			else
+				table.insert(r, v)
+			end
+		end
+		return r
+	end
+	return flat({}, l)
+end