added some exercises related to CL

[lambda.git] / rosetta1.mdwn

diff --git a/rosetta1.mdwn b/rosetta1.mdwn
index e353451..1c42a13 100644 (file)
--- a/rosetta1.mdwn
+++ b/rosetta1.mdwn
@@ -78,7 +78,7 @@ These relations are written in Haskell and OCaml as `&&`, `||`, and `not`. (Hask
 The values that are written `'true` and `'false` in Kapulet are written in Haskell as `True` and `False`, and in OCaml as just `true` and `false`. (It'd be more consistent with OCaml's other naming policies for them to have said True and False<!-- other value constructors must be capitalized -->, but they didn't.) These are written `#t` and `#f` in Scheme, but in Scheme in many contexts any value that isn't `#f` will behave as though it were `#t`, even values you might think are more "false-like", like `0` and the empty list.
 <a id=truth-like></a> Thus `(if 0 'zero 'nope)` will evaluate to `'zero`.
 
 The values that are written `'true` and `'false` in Kapulet are written in Haskell as `True` and `False`, and in OCaml as just `true` and `false`. (It'd be more consistent with OCaml's other naming policies for them to have said True and False<!-- other value constructors must be capitalized -->, but they didn't.) These are written `#t` and `#f` in Scheme, but in Scheme in many contexts any value that isn't `#f` will behave as though it were `#t`, even values you might think are more "false-like", like `0` and the empty list.
 <a id=truth-like></a> Thus `(if 0 'zero 'nope)` will evaluate to `'zero`.
 

-Some Scheme implementations, such as Racket, permit `#true` and `#false` as synonyms for `#t` and `#f`.
+Some Scheme implementations, such as Racket, permit `#true` and `#false` as synonyms for `#t` and `#f`. (These aliases are also mandated in "version 7", r7rs, of the Scheme standard.)

 
 Scheme also recognizes the values `'true` and `'false`, but it treats `'false` as distinct from `#f`, and thus as a "truth-like" value, like all of its other values that aren't `#f`. Kapulet essentially took Scheme's `boolean` values and collapsed them into being a subtype of its `symbol` values.
 <!-- This is also what it does with Scheme's `char`s ?? see [[below|rosetta1#chars]] -->
 
 Scheme also recognizes the values `'true` and `'false`, but it treats `'false` as distinct from `#f`, and thus as a "truth-like" value, like all of its other values that aren't `#f`. Kapulet essentially took Scheme's `boolean` values and collapsed them into being a subtype of its `symbol` values.
 <!-- This is also what it does with Scheme's `char`s ?? see [[below|rosetta1#chars]] -->


@@ -110,7 +110,13 @@ Scheme has no infix operators. It ruthlessly demands that all functions to be ap
 
     (+ 3 2)
 
 
     (+ 3 2)
 

-and the like. Moreover, in Scheme parentheses are never optional and never redundant. In contexts like this, the parentheses are necessary to express that the function is being applied; `+ 3 2` on its own is not a complete Scheme expression. And if the `+` were surrounded by its own parentheses, as in:
+and the like. Here is an example where the function to be applied is the result of evaluating a more complex expression:
+
+    ((if #t + *) 3 2)
+
+which will evaluate to `5`, not `6`.
+
+In Scheme the parentheses are never optional and never redundant. In expressions like `(+ 3 2)`, the parentheses are necessary to express that the function is being applied; `+ 3 2` on its own is not a complete Scheme expression. And if the `+` were surrounded by its own parentheses, as in:

 
     ((+) 3 2)
 
 
     ((+) 3 2)