Move parse_sub() logic into lexer

Now the parser starts the lexer, which in turn starts the parser.
Previously, the parser started both the lexer and itself and then asked
the lexer all kinds of personal questions, like "Where are you?",
"Whatcha doin'?", and "What are you wearing?".  No one wants to know
what their lexer is wearing.  Seriously, don't ask.  Parsers should mind
their own business.  Social interactions and personal questions between
code modules should be kept to a minimum.

1 files changed, 44 insertions, 22 deletions

diff --git a/parsing/lexer.sh b/parsing/lexer.sh
index 928021e..a3ab762 100644
--- a/parsing/lexer.sh
+++ b/parsing/lexer.sh
@@ -1,5 +1,6 @@
 fname=
 lineno=
+start=
 c=
 tok=
 tokens=
@@ -399,9 +400,9 @@ scan_wordexp()
 					;;
 				*)
 					# Command substitution
-					if ! res="$(parse_sub "${fname}" \
-							${lineno} "${c}" false)"
-					then
+					if ! res="$(run_sublexer "sub${fname}" \
+							${lineno} "${start}" \
+							"${c}")"; then
 						exit 1
 					fi
 					ln_off=${res%%${RS}*}
@@ -411,7 +412,7 @@ scan_wordexp()
 					toks="${res%%${RS}*}"
 					lineno=${ln_off}
 					wordexp="\$(${STX}${toks}${ETX})"
-					# ")" is recognized in parse_sub().
+					# ")" is recognized in run_sublexer().
 					;;
 			esac
 			;;
@@ -608,42 +609,63 @@ error()
 	exit 1
 }
 
-init_lexer()
+run_sublexer()
 {
 	local fn="${1}"
 	local ln="${2}"
-	local char="${3}"
-	shift 3
+	local st="${3}"
+	local ch="${4}"
+	shift 4
 
+	# Initialize global variables.
 	fname="${fn}"
 	lineno=${ln}
+	start="${st}"
 	tokens=''
-	case "${char}" in
-		'')
-			pgetc
+
+	c="${ch}"
+	next
+
+	#dbg=true
+	# If this returns (does not exit), there are no errors.
+	${start}
+	case "${tok%${US}*}" in
+		T_RPAREN)
 			;;
 		*)
-			c="${char}"
+			synerr 'Missing ")"'
 			;;
 	esac
-	next
-}
 
-get_lineno()
-{
-	printf '%d' ${lineno}
+	printf "%d${RS}%c${RS}%s" ${lineno} "${c}" "${tokens}"
 	return 0
 }
 
-get_lexer_char()
+run_lexer()
 {
-	printf '%c' "${c}"
-	return 0
-}
+	local fn="${1}"
+	local st="${2}"
+	shift 2
 
-get_tokens()
-{
+	# Initialize global variables.
+	fname="${fn}"
+	lineno=1
+	start="${st}"
+	tokens=''
+
+	# Read the first character and recognize the first token.
+	pgetc
+	next
+
+	# If this returns (does not exit), there are no errors.
+	${start}
+	if ! accept T_EOF; then
+		synexp ''
+	fi
+
+	# Return the tokens.
 	printf '%s' "${tokens}"
+
 	return 0
 }