properly report and handle EOF when handling input HEAD main

this should be a robust fix for the double-termination issue when compiling

Force-Push: yes
Change-Id: Ieaacdc232ea7e3036916d81139fc5c5a41087c64

1 files changed, 14 insertions, 4 deletions

diff --git a/interpret.e b/interpret.e
index 7f839ac..7695d0b 100644
--- a/interpret.e
+++ b/interpret.e
@@ -179,7 +179,10 @@
   drop 0 ; ~ Greater than "z".
 
 
-~ Okay, this is the big one, the lexer! Wow.
+~   Okay, this is the big one, the lexer! Wow.
+~
+~   The only way this can ever return a zero-length string is if it hit EOF,
+~ and callers can rely on that.
 ~
 ~ (-- stack string occupying multiple words)
 : word
@@ -190,14 +193,21 @@
   ~ Skip whitespace.
   { key dup is-space } { drop } while
 
-  ~ Early exit if it's a zero byte.
-  dup 0 = { drop dropstring 0 exit } if
+  ~   Early exit if it's an EOF. We leave the accumulated string on the stack;
+  ~ since we're not in the loop yet, it will be empty and this will function
+  ~ as the caller's indication we're at EOF.
+  dup -1 = { drop exit } if
 
   accumulate-string
 
   {
     peek dup is-space { drop exit } if
-    dup { drop exit } unless
+
+    ~   If it's an EOF, exit, leaving the accumulated string on the stack.
+    ~ It's nonempty, since we're in the loop already, and from the caller's
+    ~ perspective it's valid input.
+    dup -1 = { drop exit } if
+
     consume accumulate-string
   } forever ;