+# HIDDEN SPACE STRING TOOLS
+temporaty_token := _+;:;+_:;+;:_:+;+:_
+hidden_space := $(empty)\7f$(empty)
+hs_hide = $(subst $(space),$(hidden_space),$(1))
+hs_unhide = $(subst $(hidden_space),$(space),$(1))
+hs_escape = $(subst $(hidden_space),$(backslash)$(space),$(1))
+hs_process = $(subst $(space),$(hidden_space),$(subst $(backslash)$(space),$(hidden_space),$(1)))
+hs_quote_all = $(foreach item,$(1),"$(call hs_unhide,$(item))")
+hs_quote_each = $(foreach item,$(1),$(if $(findstring $(esc),$(item)),"$(call hs_unhide,$(item))",$(item)))
+
+# FILE PATH TOOLS
+fp_unquote = $(subst $(quote),,$(1))
+fp_opt_quotes = $(if $(findstring $(space),$(1)),"$(1)",$(1))
+fp_no_parent_dir = $(foreach item,$(1),$(if $(findstring ..,$(item)),,$(item)))
+
+# FILE SYSTEM TOOLS
+# hs_ls doc
+# usage: $(hs_ls) | $(hs_ls_dir) | $(hs_ls_files)
+# result:
+# - for hs_ls: a list of files and directories in the current dir
+# i.e.: fileA dir1/ fileB fileC dir2/ dir3/
+# - for hs_ls_dir: a list of directories in the current dir
+# i.e.: dir1 dir2 dir3
+# - for hs_ls_file: a list of files in the current dir
+# i.e.: fileA fileB fileC
+# notes:
+# - hs_ls* functions work in current dir, you can't specify a directory
+# - hs_ls* functions do not report hidden files and directories because wildcard doesn't
+# you would never get such a list: .fileA .dir1/
+hs_ls = $(subst $(temporaty_token),$(space),$(subst ./,,$(call hs_hide,$(subst $(space)./,$(temporaty_token),$(wildcard ./*/)))))
+hs_ls_dir = $(subst /,,$(foreach item,$(hs_ls),$(if $(findstring /,$(item)),$(item),)))
+hs_ls_file = $(foreach item,$(hs_ls),$(if $(findstring /,$(item)),,$(item)))
+
+# CONTROL FLOW TOOLS
+# hs_crossloop usage: $(call hs_crossloop,<list>,<command_function>)
+# hs_crossloop will call <command_function> with the item as first parameter ($(1))
+hs_crossloop = $(call hs_unsafe_crossloop,$(call fp_no_parent_dir,$(1)),$(2))
+