Improve ergonomics and usefulness of es -e.

doc/es.1

@@ -988,6 +988,24 @@ If any element of a list is not equal to
 (or the empty string), that list is considered false.
 .PP
 The return value of an assignment operation is the assigned value.
+.PP
+When
+.I es
+is invoked with the
+.Cr \-e
+option, false return values generate the
+.Cr false
+exception.
+(See the section entitled
+.B Exceptions
+for more information about the
+.Cr false
+exception.)
+The
+.Cr false
+exception is caught and treated as a return value by the
+.Cr "<="
+construct.
 .SS "Logical Operators"
 There are a number of operators in
 .I es
@@ -1543,6 +1561,20 @@ and the signal is listed in the variable
 .Cr signals .
 .I Signame
 is the name of the signal that was raised.
+.TP
+.Cr "exit \fIcode\fP"
+Raised by the
+.Cr exit
+command.
+Causes the shell to exit with the given
+.Cr code .
+.TP
+.Cr "false \fIvalue\fP"
+Raised by the
+.Cr $&exitonfalse
+primitive when a command exits with a falsey status.
+Causes the shell to exit if not caught.
+By default, this exception is caught in an interactive shell.
 .PP
 See the builtin commands
 .Cr catch
@@ -2071,6 +2103,13 @@ If none of the
 are true, the
 .I else
 command is run.
+The
+.Cr if
+function catches any
+.Cr false
+exceptions generated from
+.IR test s
+and treats them as a false return value.
 .TP
 .Cr "limit \fR[\fP-h\fR]\fP \fI\fR[\fPresource \fR[\fPvalue\fR]\fP\fR]\fP\fP"
 Similar to the
@@ -2367,14 +2406,18 @@ may provide a builtin version of this function to handle
 shell scripts if the kernel does not.
 .TP
 .Cr "%exit-on-false \fIcmd\fP"
-Runs the command, and exits if any command
-(except those executing as the tests of conditional statements)
+Runs the command, and throws the
+.Cr false
+exception if any command (except assignments)
 returns a non-zero status.
 (This function is used in the definition of
 .Cr %dispatch
 when the shell is invoked with the
 .Cr \-e
 option.)
+The uncaught
+.Cr false
+exception causes the shell to exit.
 .TP
 .Cr "%flatten \fIseparator list\fP"
 Concatenate the elements of
@@ -2871,8 +2914,10 @@ starts with a dash
 .Rc ( - ).
 .TP
 .Cr \-e
-Exit if any command (except those executing as the tests of
-conditional statements) returns a non-zero status.
+Throw a
+.Cr false
+exception if any command (other than assignments) returns a non-zero
+status.
 .TP
 .Cr \-v
 Echo all input to standard error.

es.h

@@ -167,8 +167,8 @@ extern unsigned long evaldepth, maxevaldepth;
 
 /* glom.c */
 
-extern List *glom(Tree *tree, Binding *binding, Boolean globit);
-extern List *glom2(Tree *tree, Binding *binding, StrList **quotep);
+extern List *glom(Tree *tree, Binding *binding, Boolean globit, int evalflags);
+extern List *glom2(Tree *tree, Binding *binding, StrList **quotep, int evalflags);
 
 
 /* glob.c */

eval.c

@@ -3,6 +3,7 @@
 #include "es.h"
 
 unsigned long evaldepth = 0, maxevaldepth = MAXmaxevaldepth;
+static Boolean did_assign;
 
 static Noreturn failexec(char *file, List *args) {
 	List *fn;
@@ -46,17 +47,17 @@ extern List *forkexec(char *file, List *list, Boolean inchild) {
 }
 
 /* assign -- bind a list of values to a list of variables */
-static List *assign(Tree *varform, Tree *valueform0, Binding *binding0) {
+static List *assign(Tree *varform, Tree *valueform0, Binding *binding0, int evalflags) {
 	Ref(List *, result, NULL);
 
 	Ref(Tree *, valueform, valueform0);
 	Ref(Binding *, binding, binding0);
-	Ref(List *, vars, glom(varform, binding, FALSE));
+	Ref(List *, vars, glom(varform, binding, FALSE, evalflags));
 
 	if (vars == NULL)
 		fail("es:assign", "null variable name");
 
-	Ref(List *, values, glom(valueform, binding, TRUE));
+	Ref(List *, values, glom(valueform, binding, TRUE, evalflags));
 	result = values;
 
 	for (; vars != NULL; vars = vars->next) {
@@ -76,12 +77,13 @@ static List *assign(Tree *varform, Tree *valueform0, Binding *binding0) {
 	}
 
 	RefEnd4(values, vars, binding, valueform);
+	did_assign = TRUE;
 	RefReturn(result);
 }
 
 /* letbindings -- create a new Binding containing let-bound variables */
 static Binding *letbindings(Tree *defn0, Binding *outer0,
-			    Binding *context0, int UNUSED evalflags) {
+			    Binding *context0, int evalflags) {
 	Ref(Binding *, binding, outer0);
 	Ref(Binding *, context, context0);
 	Ref(Tree *, defn, defn0);
@@ -93,8 +95,8 @@ static Binding *letbindings(Tree *defn0, Binding *outer0,
 
 		Ref(Tree *, assign, defn->u[0].p);
 		assert(assign->kind == nAssign);
-		Ref(List *, vars, glom(assign->u[0].p, context, FALSE));
-		Ref(List *, values, glom(assign->u[1].p, context, TRUE));
+		Ref(List *, vars, glom(assign->u[0].p, context, FALSE, evalflags));
+		Ref(List *, values, glom(assign->u[1].p, context, TRUE, evalflags));
 
 		if (vars == NULL)
 			fail("es:let", "null variable name");
@@ -175,8 +177,8 @@ static List *forloop(Tree *defn0, Tree *body0,
 			continue;
 		Ref(Tree *, assign, defn->u[0].p);
 		assert(assign->kind == nAssign);
-		Ref(List *, vars, glom(assign->u[0].p, outer, FALSE));
-		Ref(List *, list, glom(assign->u[1].p, outer, TRUE));
+		Ref(List *, vars, glom(assign->u[0].p, outer, FALSE, evalflags));
+		Ref(List *, list, glom(assign->u[1].p, outer, TRUE, evalflags));
 		if (vars == NULL)
 			fail("es:for", "null variable name");
 		for (; vars != NULL; vars = vars->next) {
@@ -235,29 +237,29 @@ static List *forloop(Tree *defn0, Tree *body0,
 
 /* matchpattern -- does the text match a pattern? */
 static List *matchpattern(Tree *subjectform0, Tree *patternform0,
-			  Binding *binding) {
+			  Binding *binding, int evalflags) {
 	Boolean result;
 	List *pattern;
 	Ref(Binding *, bp, binding);
 	Ref(Tree *, patternform, patternform0);
-	Ref(List *, subject, glom(subjectform0, bp, TRUE));
+	Ref(List *, subject, glom(subjectform0, bp, TRUE, evalflags));
 	Ref(StrList *, quote, NULL);
-	pattern = glom2(patternform, bp, &quote);
+	pattern = glom2(patternform, bp, &quote, evalflags);
 	result = listmatch(subject, pattern, quote);
 	RefEnd4(quote, subject, patternform, bp);
 	return result ? ltrue : lfalse;
 }
 
 /* extractpattern -- Like matchpattern, but returns matches */
 static List *extractpattern(Tree *subjectform0, Tree *patternform0,
-			    Binding *binding) {
+			    Binding *binding, int evalflags) {
 	List *pattern;
 	Ref(List *, result, NULL);
 	Ref(Binding *, bp, binding);
 	Ref(Tree *, patternform, patternform0);
-	Ref(List *, subject, glom(subjectform0, bp, TRUE));
+	Ref(List *, subject, glom(subjectform0, bp, TRUE, evalflags));
 	Ref(StrList *, quote, NULL);
-	pattern = glom2(patternform, bp, &quote);
+	pattern = glom2(patternform, bp, &quote, evalflags);
 	result = (List *) extractmatches(subject, pattern, quote);
 	RefEnd4(quote, subject, patternform, bp);
 	RefReturn(result);
@@ -280,14 +282,14 @@ extern List *walk(Tree *tree0, Binding *binding0, int flags) {
 	    case nWord: case nThunk: case nLambda: case nCall: case nPrim: {
 		List *list;
 		Ref(Binding *, bp, binding);
-		list = glom(tree, binding, TRUE);
+		list = glom(tree, binding, TRUE, flags);
 		binding = bp;
 		RefEnd(bp);
 		return eval(list, binding, flags);
 	    }
 
 	    case nAssign:
-		return assign(tree->u[0].p, tree->u[1].p, binding);
+		return assign(tree->u[0].p, tree->u[1].p, binding, flags);
 
 	    case nLet: case nClosure:
 		Ref(Tree *, body, tree->u[1].p);
@@ -301,12 +303,12 @@ extern List *walk(Tree *tree0, Binding *binding0, int flags) {
 
 	    case nFor:
 		return forloop(tree->u[0].p, tree->u[1].p, binding, flags);
-	
+
 	    case nMatch:
-		return matchpattern(tree->u[0].p, tree->u[1].p, binding);
+		return matchpattern(tree->u[0].p, tree->u[1].p, binding, flags);
 
 	    case nExtract:
-		return extractpattern(tree->u[0].p, tree->u[1].p, binding);
+		return extractpattern(tree->u[0].p, tree->u[1].p, binding, flags);
 
 	    default:
 		panic("walk: bad node kind %d", tree->kind);
@@ -378,6 +380,7 @@ extern List *eval(List *list0, Binding *binding0, int flags) {
 		return ltrue;
 	}
 	assert(list->term != NULL);
+	did_assign = FALSE;
 
 	if ((cp = getclosure(list->term)) != NULL) {
 		switch (cp->tree->kind) {
@@ -418,7 +421,7 @@ extern List *eval(List *list0, Binding *binding0, int flags) {
 			EndExceptionHandler
 			break;
 		    case nList: {
-			Ref(List *, lp, glom(cp->tree, cp->binding, TRUE));
+			Ref(List *, lp, glom(cp->tree, cp->binding, TRUE, flags));
 			list = append(lp, list->next);
 			RefEnd(lp);
 			goto restart;
@@ -478,8 +481,10 @@ extern List *eval(List *list0, Binding *binding0, int flags) {
 
 done:
 	--evaldepth;
-	if ((flags & eval_exitonfalse) && !istrue(list))
-		esexit(exitstatus(list));
+	if ((flags & eval_exitonfalse) && !istrue(list) && !did_assign) {
+		Term *t = mkstr("false");
+		throw(mklist(t, list));
+	}
 	RefEnd2(funcname, binding);
 	RefReturn(list);
 }

glom.c

@@ -149,7 +149,7 @@ static List *subscript(List *list, List *subs) {
 }
 
 /* glom1 -- glom when we don't need to produce a quote list */
-static List *glom1(Tree *tree, Binding *binding) {
+static List *glom1(Tree *tree, Binding *binding, int evalflags) {
 	Ref(List *, result, NULL);
 	Ref(List *, tail, NULL);
 	Ref(Tree *, tp, tree);
@@ -179,7 +179,7 @@ static List *glom1(Tree *tree, Binding *binding) {
 			tp = NULL;
 			break;
 		case nVar:
-			Ref(List *, var, glom1(tp->u[0].p, bp));
+			Ref(List *, var, glom1(tp->u[0].p, bp, evalflags));
 			tp = NULL;
 			for (; var != NULL; var = var->next) {
 				list = listcopy(varlookup(getstr(var->term), bp));
@@ -196,29 +196,36 @@ static List *glom1(Tree *tree, Binding *binding) {
 			RefEnd(var);
 			break;
 		case nVarsub:
-			list = glom1(tp->u[0].p, bp);
+			list = glom1(tp->u[0].p, bp, evalflags);
 			if (list == NULL)
 				fail("es:glom", "null variable name in subscript");
 			if (list->next != NULL)
 				fail("es:glom", "multi-word variable name in subscript");
 			Ref(char *, name, getstr(list->term));
 			list = varlookup(name, bp);
-			Ref(List *, sub, glom1(tp->u[1].p, bp));
+			Ref(List *, sub, glom1(tp->u[1].p, bp, evalflags));
 			tp = NULL;
 			list = subscript(list, sub);
 			RefEnd2(sub, name);
 			break;
 		case nCall:
-			list = listcopy(walk(tp->u[0].p, bp, 0));
+			ExceptionHandler
+				list = listcopy(walk(tp->u[0].p, bp, evalflags & eval_exitonfalse));
+			CatchException (e)
+				if (!termeq(e->term, "false"))
+					throw(e);
+				else
+					list = e->next;
+			EndExceptionHandler
 			tp = NULL;
 			break;
 		case nList:
-			list = glom1(tp->u[0].p, bp);
+			list = glom1(tp->u[0].p, bp, evalflags);
 			tp = tp->u[1].p;
 			break;
 		case nConcat:
-			Ref(List *, l, glom1(tp->u[0].p, bp));
-			Ref(List *, r, glom1(tp->u[1].p, bp));
+			Ref(List *, l, glom1(tp->u[0].p, bp, evalflags));
+			Ref(List *, r, glom1(tp->u[1].p, bp, evalflags));
 			tp = NULL;
 			list = concat(l, r);
 			RefEnd2(r, l);
@@ -243,7 +250,7 @@ static List *glom1(Tree *tree, Binding *binding) {
 }
 
 /* glom2 -- glom and produce a quoting list */
-extern List *glom2(Tree *tree, Binding *binding, StrList **quotep) {
+extern List *glom2(Tree *tree, Binding *binding, StrList **quotep, int evalflags) {
 	Ref(List *, result, NULL);
 	Ref(List *, tail, NULL);
 	Ref(StrList *, qtail, NULL);
@@ -270,22 +277,22 @@ extern List *glom2(Tree *tree, Binding *binding, StrList **quotep) {
 			tp = NULL;
 			break;
 		case nList:
-			list = glom2(tp->u[0].p, bp, &qlist);
+			list = glom2(tp->u[0].p, bp, &qlist, evalflags);
 			tp = tp->u[1].p;
 			break;
 		case nConcat:
 			Ref(List *, l, NULL);
 			Ref(List *, r, NULL);
 			Ref(StrList *, ql, NULL);
 			Ref(StrList *, qr, NULL);
-			l = glom2(tp->u[0].p, bp, &ql);
-			r = glom2(tp->u[1].p, bp, &qr);
+			l = glom2(tp->u[0].p, bp, &ql, evalflags);
+			r = glom2(tp->u[1].p, bp, &qr, evalflags);
 			list = qconcat(l, r, ql, qr, &qlist);
 			RefEnd4(qr, ql, r, l);
 			tp = NULL;
 			break;
 		default:
-			list = glom1(tp, bp);
+			list = glom1(tp, bp, evalflags);
 			Ref(List *, lp, list);
 			for (; lp != NULL; lp = lp->next)
 				qlist = mkstrlist(QUOTED, qlist);
@@ -316,14 +323,14 @@ extern List *glom2(Tree *tree, Binding *binding, StrList **quotep) {
 }
 
 /* glom -- top level glom dispatching */
-extern List *glom(Tree *tree, Binding *binding, Boolean globit) {
+extern List *glom(Tree *tree, Binding *binding, Boolean globit, int evalflags) {
 	if (globit) {
 		Ref(List *, list, NULL);
 		Ref(StrList *, quote, NULL);
-		list = glom2(tree, binding, &quote);
+		list = glom2(tree, binding, &quote, evalflags);
 		list = glob(list, quote);
 		RefEnd(quote);
 		RefReturn(list);
 	} else
-		return glom1(tree, binding);
+		return glom1(tree, binding, evalflags);
 }