consolidate fixed font handling

Util/ioutil.dcl

@@ -28,3 +28,5 @@ getPenAttributeColour	:: ![.PenAttribute] -> Colour;
 getPenAttributeBack		:: ![.PenAttribute] -> Colour;
 seqmap					:: (.a -> .(.b -> .b)) ![.a] !.b -> .b;
 notEmpty s				:== not (isEmpty s)
+lisFixedWidth			:: !.FontName !*Picture -> (!Bool,!*Picture)
+lfilter					:: ![.Bool] ![.a] -> [.a]

Util/ioutil.icl

@@ -147,3 +147,19 @@ seqmap f [h:t] e
 
 notEmpty s		:== not (isEmpty s)
 
+//--
+
+lisFixedWidth :: !.FontName !*Picture -> (!Bool,!*Picture)
+lisFixedWidth fontname env
+  # ((ok,font),   env) = openFont {fName=fontname,fSize=12,fStyles=[]} env
+  | not ok = (ok,env)
+//  # (wide,	 env) = getFontCharWidth font 'M' env
+//	(narrow, env) = getFontCharWidth font 'i' env
+  # ([wide,narrow:_], env)	= getFontCharWidths font ['M','i'] env
+  = (wide == narrow, env)
+
+lfilter :: ![.Bool] ![.a] -> [.a]
+lfilter [True:r] [a:x]	= [a:lfilter r x]
+lfilter [_:r] [_:x] = lfilter r x
+lfilter _ _				= []
+