From 5f1a136992dd5882d44e16de8955cb9947e86927 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Georges=20Dup=C3=A9ron?= <georges.duperon@gmail.com>
Date: Thu, 28 Feb 2019 00:00:50 +0100
Subject: [PATCH] Simple lexer for micro-scheme

---
 micro-scheme/micro-scheme.sh | 83 ++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100755 micro-scheme/micro-scheme.sh

diff --git a/micro-scheme/micro-scheme.sh b/micro-scheme/micro-scheme.sh
new file mode 100755
index 0000000..ea2a9c5
--- /dev/null
+++ b/micro-scheme/micro-scheme.sh
@@ -0,0 +1,83 @@
+#!/bin/sh
+
+stack_init_name_unit() {
+  eval "stacklast_${1}="
+}
+
+stack_push_name_hex_unit() {
+  # args:     $1 must be an [a-z]+ name
+  #           $2 must be a hexadecimal string
+  # input:    stacklast_$1
+  # output:   stacklast_$1 stack_$1_${!stacklast_$1}
+  # clobbers: stacklast
+  # warning:  does no attempt to escape ", \, $, space and so on in any of the inputs or outputs.
+  eval stacklast='${'stacklast_${1}'}'
+  stacklast=$((${stacklast}+1))
+  echo stack_${1}_${stacklast}='"'${2}'"'
+  eval stack_${1}_${stacklast}='"'${2}'"'
+  eval stacklast_${1}=${stacklast}
+}
+
+stack_len_name_int() {
+  # args:     $1 must be an [a-z]+ name
+  # input:    stacklast_$1
+  # output:   stdout=${!stacklast_$1}
+  # clobbers: nothing
+  # warning:  does no attempt to escape ", \, $, space and so on in any of the inputs or outputs.
+  eval 'printf %s ${'stacklast_${1}'}'
+}
+
+stack_pop_name_result_unit() {
+  # args:     $1 must be an [a-z]+ name
+  # input:    stacklast_$1
+  # output:   stacklast_$1 stack_$1_${!stacklast_$1}
+  # clobbers: stacklast
+  # warning:  does no attempt to escape ", \, $, space and so on in any of the inputs or outputs.
+  eval stacklast='${'stacklast_${1}'}'
+  eval $2'="${'stack_${1}_${stacklast}'}"'
+  stacklast=$((${stacklast}-1))
+  eval stacklast_${1}=${stacklast}
+}
+
+stack_peek_name_hex() {
+  # args:     $1 must be an [a-z]+ name
+  # input:    stacklast_$1 stack_$1_${!stacklast_$1}
+  # output:   stdout
+  # clobbers: stacklast
+  # warning:  does no attempt to escape ", \, $, space and so on in any of the inputs or outputs.
+  eval stacklast='${'stacklast_${1}'}'
+  eval 'printf %s "${'stack_${1}_${stacklast}'}"'
+}
+
+stack_init_name_unit parse_stack
+stack_push_name_hex_unit parse ''
+
+printf '(+ 1   ( +  22 345 ))' | \
+od -v -A n -t x1 | sed -e 's/^ //' | tr ' ' \\n | (while read c; do
+  case "$c" in
+   # Open paren
+   28) if test "x$(stack_peek_name_hex parse)" = 'x'; then
+         stack_pop_name_result_unit parse current
+       fi
+       stack_push_name_hex_unit parse 28
+       stack_push_name_hex_unit parse '';;
+   # Close paren
+   29) if test "x$(stack_peek_name_hex parse)" = 'x'; then
+         stack_pop_name_result_unit parse current
+       fi
+       stack_push_name_hex_unit parse 29;;
+   # Space
+   20) if test "x$(stack_peek_name_hex parse)" != 'x'; then
+         stack_push_name_hex_unit parse ''
+       fi;;
+   # identifier character
+   *) stack_pop_name_result_unit parse current
+      stack_push_name_hex_unit parse "$current$c";;
+  esac
+done
+
+while test "x$(stack_len_name_int parse)" != 'x0'; do
+  stack_pop_name_result_unit parse tmp
+  echo "$tmp 0a"
+done | tac | xxd -ps -r
+)