Add UPLINE character. Fixes #95

intro.md

@@ -183,6 +183,7 @@ helpful for this sort of construction:
     QUOTE
     DQUOTE
     BQUOTE
+    UPLINE
 
 These all evaluate to atoms whose names are the unreadable characters,
 some of which may be helpful for text games and other diversions:
@@ -211,6 +212,11 @@ some of which may be helpful for text games and other diversions:
     ()
     >
 
+The `UPLINE` character, in particular, which moves the cursor to the
+beginning of the previous line, is useful for making command-line
+output which repeatedly updates the line in place, rather than
+printing multiple lines.
+
 ## Functions
 
 Functions come in two flavors: temporary functions, called "lambda"

l1.md

@@ -183,6 +183,7 @@ helpful for this sort of construction:
     QUOTE
     DQUOTE
     BQUOTE
+    UPLINE
 
 These all evaluate to atoms whose names are the unreadable characters,
 some of which may be helpful for text games and other diversions:
@@ -211,6 +212,11 @@ some of which may be helpful for text games and other diversions:
     ()
     >
 
+The `UPLINE` character, in particular, which moves the cursor to the
+beginning of the previous line, is useful for making command-line
+output which repeatedly updates the line in place, rather than
+printing multiple lines.
+
 ## Functions
 
 Functions come in two flavors: temporary functions, called "lambda"

lisp/builtin.go

@@ -30,6 +30,7 @@ func InitGlobals() Env {
 	globals.Set("QUOTE", Atom{"'"})
 	globals.Set("BQUOTE", Atom{"`"})
 	globals.Set("DQUOTE", Atom{"\""})
+	globals.Set("UPLINE", Atom{"\033[F"})
 	return globals
 }