From ac6cc6b2405bb6d3775344a873fb1172f38f1c7e Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Sat, 20 Feb 2016 12:23:16 -0500
Subject: Implement command substitution (warning: ugly and broken)

---
diff --git a/parsing/lexer.sh b/parsing/lexer.sh
index b03878d..1e9b2e0 100644
--- a/parsing/lexer.sh
+++ b/parsing/lexer.sh
@@ -276,6 +276,7 @@ scan_wordexp()
 	local res=
 	local param=
 	local word=
+	local toks=
 
 	wordexp=''
 	ln_off=0
@@ -398,8 +399,30 @@ scan_wordexp()
 					;;
 				*)
 					# Command substitution
-					synerr 'Command substitution is %s' \
-						'not yet supported'
+					if ! res="$(parse_sub "${fname}" \
+							${lineno} "${c}" false)"
+					then
+						exit 1
+					fi
+					ln_off=${res%%${RS}*}
+					res="${res#*${RS}}"
+					c="${res%%${RS}*}"
+					res="${res#*${RS}}"
+					toks="${res%%${RS}*}"
+					lineno=${ln_off}
+					wordexp="\$(${STX}${toks}${ETX}"
+					# Get ")"
+					case "${c}" in
+						')')
+							wordexp="${wordexp}${c}"
+							pgetc
+							;;
+						*)
+							echo "c: '$c'" >&2
+							echo "wordexp: $wordexp" >&2
+							synerr 'Missing ")"'
+							;;
+			esac
 					;;
 			esac
 			;;
@@ -600,15 +623,35 @@ init_lexer()
 {
 	local fn="${1}"
 	local ln="${2}"
-	shift 2
+	local char="${3}"
+	shift 3
 
 	fname="${fn}"
 	lineno=${ln}
 	tokens=''
-	pgetc
+	case "${char}" in
+		'')
+			pgetc
+			;;
+		*)
+			c="${char}"
+			;;
+	esac
 	next
 }
 
+get_lineno()
+{
+	printf '%d' ${lineno}
+	return 0
+}
+
+get_lexer_char()
+{
+	printf '%c' "${c}"
+	return 0
+}
+
 get_tokens()
 {
 	printf '%s' "${tokens}"
diff --git a/parsing/parse.sh b/parsing/parse.sh
index a28aad2..4d4b9ea 100644
--- a/parsing/parse.sh
+++ b/parsing/parse.sh
@@ -583,20 +583,28 @@ sequential_sep()
 	return 1
 }
 
+# Maybe parse() should just tell the lexer what the starting production (parser
+# entry point) is.
 parse_sub()
 {
 	local fn="${1}"
 	local ln="${2}"
-	shift 2
+	local lexer_char="${3}"
+	local complete="${4}"
+	shift 3
 
-	init_lexer "${fn}" ${ln}
+	init_lexer "${fn}" ${ln} "${lexer_char}"
 
 	# If this returns (does not exit), there are no errors.
 	complete_command
-	if ! accept T_EOF; then
+	if ${complete} && ! accept T_EOF; then
 		synexp ''
 	fi
 
+	get_lineno
+	printf '%c' "${RS}"
+	get_lexer_char
+	printf '%c' "${RS}"
 	get_tokens
 
 	return 0
@@ -606,8 +614,10 @@ parse()
 {
 	local fn="${1}"
 	shift 1
+	local toks=
 
-	if parse_sub "${fn}" 1; then
+	if toks="$(parse_sub "${fn}" 1 '' true)"; then
+		printf '%s\n' "${toks#*${RS}*${RS}}"
 		return 0
 	fi
 	return 1
@@ -640,7 +650,7 @@ try()
 }
 
 #try '"foo bar" && $baz || qux' '${quux%uux  quuux'
-try '"foo bar" && $baz || qux' '${quux%uux } quuux'
+#try '"foo bar" && $baz || qux' '${quux%uux } quuux'
 #try 'foo ${bar}'
 #try 'foo ${#bar}'
 #try 'foo ${bar#baz}'
@@ -659,5 +669,5 @@ try '"foo bar" && $baz || qux' '${quux%uux } quuux'
 #try 'foo(){ bar; }'
 #try 'case foo in bar) baz;; (qux) quux;; quux);; esac'
 #try 'foo bar ( baz )'
-#try 'foo $(bar)'
+try 'foo $(bar)'
 #try 'foo $((1 + 1))'
--
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