Changeset 8734 in project

Timestamp:

02/24/08 03:41:36 (12 years ago)

Author:

graham

Message:

suggested revision for tail-call discussion

Location:

wiki

Files:

• chicken-for-ruby-programmers (modified) (2 diffs)
• orders (modified) (1 diff)

wiki/chicken-for-ruby-programmers

@@ -316 +316 @@
 because when the {{(+ (add-up-to (sub1 x)) x)}} expression is
 evaluated, the recursive call to {{add-up-to}} creates a new stack
-frame so that when it returns the x can be added to the result.
+frame so that when it returns the x can be added to the result. 
+
+[Note that this code will 'break' in Chicken too, but only for much
+larger numbers. Although Chicken doesn't have an arbitrary stack
+depth, if you try (add-up-to) on a large enough number, you'll use up
+all your system memory before getting an answer. Read on for a better
+way to write it.]
+
 All Schemes know that when there is nothing that needs to be done
 after a procedure returns, there is no point in returning to the
-procedure that called it at all, instead it can just return directly
-to the procedure that called the current procedure, so the call can
-be optimized to become a ''goto'', replacing the current stack frame:
+procedure that called it at all: instead it can just return directly
+to the procedure that called the current procedure. So the call can
+be optimized to become a ''goto'', replacing the current stack frame.
 
 Ruby still can't handle it:
@@ -354 +361 @@
 As you'll notice, this version is a lot faster in Chicken too because
 it does not have to travel back through all those empty "stack
-frames".  You can also notice the difference when you remove the stop
-condition and you look at your OS's process list.  Then Chicken's
-memory usage just keeps going up until it breaks because it can't
-allocate any more.  In the second example it will stay constant and
-simply loop forever.
+frames".  In the first example, Chicken's memory usage increases upon
+every recursion: for large numbers, it will break because it can't
+allocate any more. But in the second example, memory usage will stay
+constant and simply loop forever.
 
 === Blocks

wiki/orders

@@ -4 +4 @@
 
 There's no documentation about it right now.  Sorry.  :-(
+
+== Dependencies
+
+{{srfi-13}}
+
+== Procedures
+
+[procedure] (cmp-key cmp key)
+
+Generates an ordering procedure that applies the 'key' proc to both
+sort candidates, and compares the resulting keys using the 'cmp'
+procedure.
+
+E.g. to sort a list of integers based on their value modulo-10:
+(sort my-numbers (cmp < (cut modulo <> 10)))
+
+[procedure] (key-string< key)
+
+Generates an ordering procedure that sorts strings using string<
+(defined in SRFI-13).
+