Add doc comment, change while loop to recursion.

CraigStuntz · Jan 31, 2012 · 8614185 · 8614185
1 parent 4f54ffb
commit 8614185
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Showing 2 changed files with 13 additions and 10 deletions.
diff --git a/Lbac.Compiler/Part01-Introduction.fs b/Lbac.Compiler/Part01-Introduction.fs
@@ -20,6 +20,7 @@
             error(s + " Expected")
 
         /// <summary>
+        /// Returns argument c if lookahead equals c, throws otherwise. 
         /// Crenshaw calls this "Match", but match is reserved in F#
         /// </summary>
         member x.matchChar(c : char) = 

diff --git a/Lbac.Compiler/Part02-ExpressionParsing.fs b/Lbac.Compiler/Part02-ExpressionParsing.fs
@@ -114,16 +114,18 @@
 
         member x.expression() = 
             // <expression> ::= [<addop>] <term> [<addop> <term>]*
-            let mutable result = if isAddop x.look then
+            let head = if isAddop x.look then
-                                    [IL.Ldc_I4_0]
+                           [IL.Ldc_I4_0]
-                                 else
+                       else
-                                    x.term()
+                           x.term()
-            while isAddop x.look do
+            // rest of expression is evaluated recurively for forms like 1+2-3+4...
-                match x.look with
+            x.expressionTail head
-                | '+' -> result <- result @ x.add()
+
-                | '-' -> result <- result @ x.subtract()
+        member private x.expressionTail head = 
-                | _   -> x.expected("Addop")
+            match x.look with
-            result
+            | '+' -> x.expressionTail( head @ x.add()      )
+            | '-' -> x.expressionTail( head @ x.subtract() )
+            | _   -> head
 
         override x.compile() = 
             x.expression()