Changes between Version 21 and Version 22 of StructuredBinaryData

Timestamp:

2012-08-08T04:42:00Z (12 years ago)

Author:

Sean Bartell

Comment:

Better expressions implemented

StructuredBinaryData

@@ -166 +166 @@
 it is decoded.
 
+== Expressions ==
+
 Transforms can have parameters that affect how they decode data:
 {{{
@@ -176 +178 @@
 }}}
 When such a transform is used, expressions must be given to calculate its
-parameters. Currently, the only possible expressions are parameters given to
-the current transform, boolean and integer literals, and previously decoded
-fields in the current `struct` or an outer `struct`:
+parameters. The basic terms used in expressions are parameters given to the
+current transform, boolean and integer literals, and previously decoded fields
+in the current `struct` or an outer `struct`:
 {{{
 transform item(little_endian) = struct {
@@ -186 +188 @@
 };
 }}}
+You can also use `+`, `-`, `*`, and parentheses as you would expect.
+
+Expressions can also be used as transforms themselves, in two ways. First, an
+expression referring to `in` can be used to decode a value, such as
+`.num_bytes <- (in * 4) <- uint32le;`. Second, an expression that doesn’t refer
+to `in` can be used as a transform that takes an empty blob and evaluates the
+expression: for example, `.num_total <- (.num_short + .num_long);` could be
+used in a `struct`. In both cases, the parentheses are mandatory.
 
 == Structs ==
@@ -277 +287 @@
    printed instead; Bithenge should not try to look in the `if` when searching
    for `.non_existent`.
- Complex expressions:: Expressions that use operators or call transforms.
+ Complex expressions:: More operators, and expressions that call transforms.
  Better error reporting:: errno.h is intended for system call errors; when
    other errors occur, a more helpful error message should be printed, like