!!! Upgrading Your Program To Orc 2.0

Orc 2.0 improves the syntax of the Orc language in many ways, but some of these changes require existing Orc programs to be modified.  Here is a topical list of the most significant such changes.  The full list of what's new in Orc 2.0 is in [Orc 2.0 Release Notes].

!! Comparison

* Less than {{<}} and greater than {{>}} have changed to {{<:}} and {{:>}} to remove ambiguity with the pruning and sequential combinators.

!! If Then Else

* Some uses of {{if then else}} that were previously un-parenthesised may now require parenthesis.  (The special parser rules regarding {{if then else}} and the sequential combinator {{>>}} have been removed.)
* The undocumented option to omit the {{else}} clause has been eliminated.
* The {{if}} site has been renamed to {{Ift}}.

!! Site Names

* All library site names are consistently capitalized.  Sites that predated this convention have been brought into conformance: {{Let}}, {{Print}}, {{Println}}, {{Error}}, {{Read}}, {{Write}}, {{Floor}}, {{Ceil}}, {{Random}}, {{URandom}}.
* Some library sites have been renamed for clarity and consistency:
** {{IArray}} is now {{Table}}.
** {{Rtimer}} is now {{Rwait}}. {{Clock}} is now {{Rclock}}.
** {{Buffer}} is now {{Channel}}. {{~BoundedBuffer}} is now {{~BoundedChannel}}.
** "Nonblocking" sites, with the suffix "{{nb}}", are now "definite" sites, with the suffix "{{D}}".

!! Def Body Parsing Ambiguity

This program excerpt could be parsed in two ways:
{{{
def f() = 1
- 2
}}}
Namely, as a {{def}} with a body {{1 - 2}}, or with a body {{1}}, followed by a goal expression {{-2}}.

* Previously, the parser treated newlines specially to try to disambiguate these cases.  That has been removed, because it imposed surprising-to-new-users restrictions on the placement of newlines.
* This ambiguity happens most commonly with goal expressions that start with a parenthesis {{(}} or a minus {{-}}.
* To eliminate the ambiguity, one can add a {{signal >>}} to the beginning of the goal expression.
{{{
def f() = 1
signal >> - 2
}}}

!! Definitions and Imports

* The import declarations for {{site}}, {{class}}, and {{type}} are now preceded by the keyword {{import}} and the Java class name is quoted.  For example, {{import class ~TreeSet = "java.util.~TreeSet"}}.
* {{def capsule}} is now {{def class}}.

!! Patterns

* The equality {{=x}} pattern is gone. Use the new guard feature instead, for example, {{def f(x,y) if (x = y) = ...}}.

!! Arrays

* Arrays have no methods, and have only a length field.
** The {{get}} and {{set}} methods are replaced by the use of elements as {{Ref}}s (see below).
** The {{slice}} and {{fill}} methods are replaced by the library functions {{sliceArray}} and {{fillArray}}.
** The {{length}} method is replaced by the length field, accessed as {{length?}}.
* Array elements are {{Ref}}s, so they are read like {{a(3)?}} and written like {{a(3) := 5}}.

!! Currying

* The currying syntactic form was removed, since it held traps for the unwary -- it implicitly made functions strict.  It also distractingly complicated the presentation of the language's syntax.
* Replace currying with explicit uses of {{lambda}}.