impls/bash: Minor changes to make it run under OSH

OSH is a bash-compatible shell: https://www.oilshell.org/

reader.sh:

- Put the constant regex pattern in a string literal.  This simplifies
  it by removing mixed regex vs. shell quoting, and implicit
  concatenation with $'\n'.

  This is suggested by the bash manual:
  https://www.gnu.org/software/bash/manual/bash.html#Conditional-Constructs

  "Storing the regular expression in a shell variable is often a useful
  way to avoid problems with quoting characters that are special to the
  shell."

- Initialize __reader_tokens as an array, not a string.

  https://www.oilshell.org/release/0.8.pre6/doc/known-differences.html#values-are-tagged-with-types-not-cells

env.sh:

Simplify quoting in 'eval' expressions.  This quotes associative array keys,
which is required by OSH to avoid dynamic parsing.

  https://www.oilshell.org/release/0.8.pre6/doc/known-differences.html#strings-vs-bare-words-in-array-indices
  http://www.oilshell.org/blog/2016/10/20.html

core.sh:

Quote associative array keys.  '<' and '>' are shell operators and OSH doesn't
have a special case when inside [].

----

With this change, OSH can run tests just like bash, e.g.:

$ osh impls/bash/stepA_mal.sh tests/step4_if_fn_do.mal

----

Test results are the same before and after this change:

$ NO_DOCKER=1 ./.travis_test.sh test bash

FAILURES:
SOFT FAILED TEST (line 295): (f (+ 1 1)) -> ['',true]:
    Expected : '.*\ntrue'
    Got      : '(f (+ 1 1))\nfalse'

TEST RESULTS (for ../tests/stepA_mal.mal):
    1: soft failing tests
    0: failing tests
  106: passing tests
  107: total tests

impls/bash/core.sh

@@ -376,10 +376,10 @@ declare -A core_ns=(
     [readline]=readline
     [read-string]=read_string
     [slurp]=slurp
-    [<]=num_lt
-    [<=]=num_lte
-    [>]=num_gt
-    [>=]=num_gte
+    ['<']=num_lt
+    ['<=']=num_lte
+    ['>']=num_gt
+    ['>=']=num_gte
     [+]=num_plus
     [-]=num_minus
     [__STAR__]=num_multiply

impls/bash/env.sh

@@ -48,7 +48,7 @@ ENV_FIND () {
         r="${1}"
     else
         local obj="${ANON["${1}"]}"
-        eval local outer="\${${obj}["__outer__"]}"
+        eval 'local outer=${'${obj}'["__outer__"]}'
         if [[ "${outer}" && "${outer}" != "${__nil}" ]]; then
             ENV_FIND "${outer}" "${2}"
         else
@@ -66,7 +66,7 @@ ENV_GET () {
     local key="${ANON["${2}"]}"
     if [[ "${r}" ]]; then
         local obj="${ANON["${env}"]}"
-        eval r="\${${obj}["${key}"]}"
+        eval 'r=${'${obj}'["'${key}'"]}'
     else
         _error "'${key}' not found"
     fi

impls/bash/reader.sh

@@ -103,6 +103,8 @@ READ_FORM () {
     esac
 }
 
+TOKEN_PAT=$'^^([][{}\\(\\)^@])|^(~@)|^("(\\\\.|[^\\"])*"?)|^(;[^\n]*)|^([~\'`])|^([^][ ~`\'";{}\\(\\)^@,\n]+)|^(,)|^([[:space:]]+)'
+
 # Returns __reader_tokens as an indexed array of tokens
 TOKENIZE () {
     local data="${*}"
@@ -114,14 +116,14 @@ TOKENIZE () {
     local str=
 
     __reader_idx=0
-    __reader_tokens=
+    declare -a -g __reader_tokens=()  # global array
     while true; do
         if (( ${#str} < ( chunksz / 2) )) && (( chunk < datalen )); then
             str="${str}${data:${chunk}:${chunksz}}"
             chunk=$(( chunk + ${chunksz} ))
         fi
         (( ${#str} == 0 )) && break
-        [[ "${str}" =~ ^^([][{}\(\)^@])|^(~@)|^(\"(\\.|[^\\\"])*\"?)|^(;[^$'\n']*)|^([~\'\`])|^([^][ ~\`\'\";{}\(\)^@\,$'\n']+)|^(,)|^([[:space:]]+) ]]
+        [[ "${str}" =~ ${TOKEN_PAT} ]]
         token=${BASH_REMATCH[0]}
         str="${str:${#token}}"
         token="${token}"