a brainf*ck interpreter written in pure Makefile (GNU Make)

brainf_ck.mk

# basic numbers
n0:=
n1:=+
n2:=+ +

# number operators
add=$(1) $(2)
incr=+ $(1)
sub=$(strip $(wordlist $(words $(call add,$(2),$(n1))),10000,$(1)))
decr=$(wordlist 2,10000,$(1))
mul=$(if $(2),$(1) $(call mul,$(1),$(call decr,$(2))),)
lt =$(if $(2),$(if $(1),$(call lt,$(call decr,$(1)),$(call decr,$(2))),true),)

# more numbers
n4  :=$(call add,$(n2),$(n2))
n16 :=$(call mul,$(n4),$(n4))
n32 :=$(call add,$(n16),$(n16))
n33 :=$(call incr,$(n32))
n64 :=$(call mul,$(n16),$(n4))
n128:=$(call add,$(n64),$(n64))
n127:=$(call decr,$(n128))
n256:=$(call mul,$(n16),$(n16))
n255:=$(call sub,$(n256),$(n1))

# to char
comma:=,
chars:=! " \# $$ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z [ \\ ] ^ _ ` a b c d e f g h i j k l m n o p q r s t u v w x y z { | } ~
to_char=$(if $(call lt,$(n32),$(1)),$(word $(words $(call sub,$(1),$(n32))),$(chars)),$(if $(filter $(words $(1)),32), ,\$(words $(1))))

current_buffer=buffer$(words $(pt))

# commands

# +
define cmd_incr
  $(if $(filter $(words $($(current_buffer))),255),\
    $(eval $(current_buffer):=),\
    $(eval $(current_buffer)+=+))
endef

# -
define cmd_decr
  $(if $($(current_buffer)),\
    $(eval $(current_buffer):=$(call decr,$($(current_buffer)))),\
    $(eval $(current_buffer):=$(n255)))
endef

# >
define cmd_next
  $(eval pt+=+)
endef

# <
define cmd_prev
  $(if $(pt),\
    $(eval pt:=$(wordlist 2,10000,$(pt))),\
    $(error buffer under flow!))
endef

# .
define cmd_write
  $(if $(filter $(words $($(current_buffer))),10),\
    $(info $(output))$(eval output:=),\
    $(eval output:=$(output)$(call to_char,$($(current_buffer)))))
endef

# ,
define cmd_read
  $(if $(USE_SHELL),\
    $(eval $(current_buffer):=$(shell $(read_command))),\
    $(error read command (",") is not supported))
endef

define read_command
OLDIFS="$$IFS";
IFS="";
read -n1 x;
if [[ "$$x" = ' ' ]]; then
  x=32;
elif [[ "$$x" = $$'
' ]]; then
  x=10;
else
  x="'$$x";
fi;
IFS="$$OLDIFS";
for i in `seq 1 $$(printf %d $$x)`; do
  echo -n "+ ";
done;
endef

# [
define cmd_loop_start
  $(if $($(current_buffer)),\
    $(eval loops_length+=+)$(eval loops_$(words $(loops_length)):=$(pc)),\
    $(call loop_skip,$(zero)))
endef

define loop_skip
  $(if $(filter $(current_source),]),\
    $(if $(filter $(words $(1)),1),,\
      $(eval pc+=+)$(call loop_skip,$(call decr,$(1)))),\
    $(if $(filter $(current_source),[),\
      $(eval pc+=+)$(call loop_skip,$(call incr,$(1))),\
      $(if $(current_source),\
        $(eval pc+=+)$(call loop_skip,$(1)),\
        $(error missing end of brace))))
endef

# ]
define cmd_loop_end
  $(if $(loops_length),\
    $(eval pc:=$(call decr,$(loops_$(words $(loops_length)))))$(eval loops_length:=$(call decr,$(loops_length)))$(eval loops:=$(wordlist 1,10000,$(loops))),\
    $(error missing start of brace))
endef

echo:=,[.,]
hello:=++++[>+<++++]>++ +++++++. ---. +++++++.. +++.
source:=$(or $(SRC),$(hello))

# convert source to list

source:=$(strip \
        $(subst +, + ,\
        $(subst -, - ,\
        $(subst >, > ,\
        $(subst <, < ,\
        $(subst ., . ,\
        $(subst $(comma), $(comma) ,\
        $(subst [, [ ,\
        $(subst ], ] ,$(source))))))))))

# execute

current_source=$(word $(words $(pc)),$(source))
char_is=$(filter $(current_source),$(1))
pc:=+
step=$(strip \
  $(if $(call char_is,+),$(cmd_incr),\
  $(if $(call char_is,-),$(cmd_decr),\
  $(if $(call char_is,>),$(cmd_next),\
  $(if $(call char_is,<),$(cmd_prev),\
  $(if $(call char_is,.),$(cmd_write),\
  $(if $(call char_is,$(comma)),$(cmd_read),\
  $(if $(call char_is,[),$(cmd_loop_start),\
  $(if $(call char_is,]),$(cmd_loop_end),)))))))))
run=$(strip $(if $(current_source),$(step)$(eval pc+=+)$(call run),))

$(call run)
$(info $(output))

all:
	@echo