From e8e6feeb95cdc3b81a2c17b5a342a3d0b170ccb4 Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <petermikkelsen10@gmail.com>
Date: Tue, 22 Feb 2022 12:29:23 +0000
Subject: Prepare for error guards

---
 apl9.h  |  1 +
 eval.c  | 28 ++++++++++++++++++++--------
 lexer.c |  7 +++++++
 3 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/apl9.h b/apl9.h
index d8afcb1..d115ea3 100644
--- a/apl9.h
+++ b/apl9.h
@@ -120,6 +120,7 @@ struct Array
 struct Statement
 {
 	int ntoks;
+	int errorguard; /* if guard != nil, is the guard an error guard? */
 	Datum **toks;
 	Statement *guard;
 	Statement *next;
diff --git a/eval.c b/eval.c
index 58a745b..4131871 100644
--- a/eval.c
+++ b/eval.c
@@ -113,24 +113,36 @@ retry:
 			int guardOK = 1;
 			if(stmt->toks[0]->tag != ArrayTag)
 				guardOK = 0;
-			else if(GetSize(stmt->toks[0]->array) != 1)
+			else if(!stmt->errorguard && GetSize(stmt->toks[0]->array) != 1)
+				guardOK = 0;
+			else if(stmt->errorguard && GetSize(stmt->toks[0]->array) < 1)
 				guardOK = 0;
 			else if(GetType(stmt->toks[0]->array) != AtypeInt)
 				guardOK = 0;
-			else if(stmt->toks[0]->array->intdata[0] != 0 && stmt->toks[0]->array->intdata[0] != 1)
+			else if(!stmt->errorguard && stmt->toks[0]->array->intdata[0] != 0 && stmt->toks[0]->array->intdata[0] != 1)
 				guardOK = 0;
-			if(!guardOK)
-				throwerror(L"Guard expected single valued boolean", EDomain);
-			else{
+			if(!guardOK){
+				if(!stmt->errorguard)
+					throwerror(L"Guard expected single valued boolean", EDomain);
+				else
+					throwerror(L"Error guard expected an array of error numbers", EDomain);
+			}else{
 				stop = 0;
-				if(stmt->toks[0]->array->intdata[0] == 1)
-					return eval(stmt->guard, toplevel);
+				if(!stmt->errorguard){
+					if(stmt->toks[0]->array->intdata[0] == 1)
+						return eval(stmt->guard, toplevel);
+				}else
+					print("Not registering error guard for error codes: %S\n", ppdatum(stmt->toks[0]));
 			}
 		}
 		if(stmt->next && !stop)
 			return eval(stmt->next, toplevel);
-		else
+		else if(!stmt->guard)
 			return stmt->toks[0];
+		else{
+			throwerror(L"No value produced", EValue);
+			return nil;
+		}
 	}else
 		return nil;
 }
diff --git a/lexer.c b/lexer.c
index 0024320..4e9a4e4 100644
--- a/lexer.c
+++ b/lexer.c
@@ -88,11 +88,18 @@ lexline(InputStream *input, int toplevel)
 		}else if(!toplevel && peek == ':'){
 			Rune buf[MAX_LINE_LENGTH];
 			Rune *p = buf;
+			int errorguard = 0;
+			if(getrune(input) == ':')
+				errorguard = 1;
+			else
+				ungetrune(input);
+
 			while((peek = getrune(input)) != L'⋄' && peek != '\n' && !inputEOF(input))
 				*p++ = peek;
 			*p = 0;
 			ungetrune(input);
 			stmt->guard = lexlinestr(buf, toplevel);
+			stmt->errorguard = errorguard;
 			stmt->ntoks--;
 		}else if(peek == '{'){
 			int unclosed = 1;
-- 
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