Even Odd in Gnu Make

Welcome to the Even Odd in Gnu Make page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

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: ;@:

Even Odd in Gnu Make was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.