Add Even Odd in Gnu Make (TheRenegadeCoder#4989)

Author: rzuckerm

archive/g/gnu-make/even-odd.mk

@@ -0,0 +1,55 @@
+USAGE := Usage: please input a number
+
+# Numbers are represented as x's so that they can be manipulated with text functions.
+# This idea is based on how the GNU Make Standard Library (https://github.com/jgrahamc/gmsl)
+# handles numbers.
+X0  :=
+X1  := x
+
+# Constants
+NUMBERS := 0 1 2 3 4 5 6 7 8 9
+EVEN_NUMBERS := 0 2 4 6 8
+
+# Get rest of words in a list
+# Arg 1: The list
+# Return: List with first word removed
+REST = $(wordlist 2,$(words $(1)),$(1))
+
+# Repeatedly apply a function
+# Arg 1: Name of function. This function must take two arguments:
+# - Function Arg1: Current value
+# - Function Arg2: New value
+# Arg 2: The list to repeated apply the function to
+# Arg 3: Initial value
+_REDUCE = $(if $(4),$(call _REDUCE,$(1),$(call $(1),$(2),$(3)),$(firstword $(4)),$(call REST,$(4))),$(call $(1),$(2),$(3)))
+REDUCE = $(call _REDUCE,$(1),$(3),$(firstword $(2)),$(call REST,$(2)))
+
+# Split number into individual digits
+# Arg 1: Number to split
+# Return: Number split into individual digits
+_SUBST_SPACE = $(subst $(2), $(2),$(1))
+SPLIT_NUMBER = $(strip $(call REDUCE,_SUBST_SPACE,$(NUMBERS),$(1)))
+
+# Indicate if valid number
+# Arg 1: Number
+# Return: $(X1) if valid number, $(X0) otherwise
+IS_VALID_NUMBER = $(if $(strip $(1)),$(if $(filter-out $(NUMBERS),$(call SPLIT_NUMBER,$(1))),$(X0),$(X1)),$(X0))
+
+# Indicate if number is even or odd
+# Arg 1: Number
+# Return: $(X1) if even, $(X0) otherwise
+IS_EVEN = $(if $(filter $(EVEN_NUMBERS),$(lastword $(call SPLIT_NUMBER,$(1)))),$(X1),$(X0))
+
+# Remove leading minus sign from input value
+ABS_VALUE := $(patsubst -%,%,$(ARGV1))
+
+# If invalid number, display usage statement
+# Else if indicate if number is even or odd
+ifeq (,$(call IS_VALID_NUMBER,$(ABS_VALUE)))
+$(info $(USAGE))
+else
+$(info $(if $(call IS_EVEN,$(ABS_VALUE)),Even,Odd))
+endif
+
+.PHONY:
+all: ;@: