From 9e2a93ddddeb89aa2512f2c6ee09a740729d9704 Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Sat, 20 Feb 2016 22:59:51 -0500
Subject: Implement arithmetic expansion

---
diff --git a/parsing/lexer.sh b/parsing/lexer.sh
index 924964e..ce39c23 100644
--- a/parsing/lexer.sh
+++ b/parsing/lexer.sh
@@ -344,8 +344,7 @@ scan_wordexp()
 			case "${c}" in
 				'(')
 					# Arithmetic expansion
-					synerr 'Arithmetic expansion is %s' \
-						'not yet supported'
+					scan_wordexp_arith
 					;;
 				*)
 					# Command substitution
@@ -391,7 +390,6 @@ scan_wordexp_param_brace()
 	local param=
 	local word=
 
-	ln_off=0
 	mod=true
 
 	lgetc
@@ -554,6 +552,63 @@ scan_param()
 	return 0
 }
 
+scan_wordexp_arith()
+{
+	local arith=
+	local paren_lvl=
+	local res=
+	local sub_wordexp=
+
+	arith=''
+	paren_lvl=0
+	while :; do
+		lgetc
+		case "${c}" in
+			'')
+				synerr 'end of file unexpected (%s)' \
+					'expecting "))"'
+				;;
+			'(')
+				arith="${arith}${c}"
+				paren_lvl=$((${paren_lvl} + 1))
+				;;
+			')')
+				if [ ${paren_lvl} -eq 0 ]; then
+					lgetc
+					case "${c}" in ')')
+						wordexp="\$((${arith}))"
+						lgetc
+						return 0
+						;;
+					esac
+					synerr 'Arithmetic expansion: ")" %s' \
+						'unexpected'
+				fi
+				arith="${arith}${c}"
+				paren_lvl=$((${paren_lvl} - 1))
+				;;
+			'$')
+				lgetc
+				if ! res=$(scan_wordexp); then
+					exit 1
+				fi
+				ln_off=${res%%${RS}*}
+				res="${res#*${RS}}"
+				c="${res%%${RS}*}"
+				res="${res#*${RS}}"
+				sub_wordexp="${res%%${RS}*}"
+				# We must advance lineno because scan_wordexp()
+				# was run in a subshell.
+				lineno=$((${lineno} + ${ln_off}))
+				arith="${arith}${sub_wordexp}"
+				;;
+			*)
+				arith="${arith}${c}"
+				;;
+		esac
+	done
+}
+
 #
 # Interface
 #
diff --git a/parsing/parse.sh b/parsing/parse.sh
index 8f73b32..6508142 100644
--- a/parsing/parse.sh
+++ b/parsing/parse.sh
@@ -624,12 +624,12 @@ try()
 }
 
 #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}'
-try 'foo ${#bar#}'
-try 'foo ${^}'
+#try '"foo bar" && $baz || qux' '${quux%uux } quuux'
+#try 'foo ${bar}'
+#try 'foo ${#bar}'
+#try 'foo ${bar#baz}'
+#try 'foo ${#bar#}'
+#try 'foo ${^}'
 #try 'foo `bar`'
 #try 'foo &&'
 #try '{ foo; }'
@@ -649,3 +649,7 @@ try 'foo ${^}'
 #try 'foo $(bar) baz'
 #try 'foo$(bar$(baz))qux'
 #try 'foo $((1 + 1))'
+try '$((1 + 1))'
+try '$((1 + (1 + 1)))'
+try '$((1 + $(foo) + 1))'
+try '$((1'
--
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