X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=rosetta1.mdwn;h=1c42a1337c03686ed227e190918aa44a86ffa57b;hp=e353451112c179032336e5b460cd7b6be40cecc6;hb=26c8d6da76887c3756f2ce856b03f490945814c0;hpb=e4e1e0f2f5156d78cd2d896d9f3c711babd7ac15 diff --git a/rosetta1.mdwn b/rosetta1.mdwn index e3534511..1c42a133 100644 --- 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, 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. 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. @@ -110,7 +110,13 @@ Scheme has no infix operators. It ruthlessly demands that all functions to be ap (+ 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)