Carl also refers to Rebol scripts as expressions. He says "REBOL Expressions are based on this concept: you combine values and words into blocks".
The chapter Expressions in the Rebol User Guide is pretty much essential reading.
@GiuseppeChillemi, lexical scanning is the first step. Parsing and tokenizing the input to find Red values in the text, and determining if the input is valid. That is, it contains all valid Red values.
At that point you have a block of values. Think about how you, as a human, interpret that. You know some values are direct values, like numbers. But what happens when you find a word? You need to determine what to do. What kind of word is it? What is the behavior of each kind of word?
Glad if it helped a bit @RiVeND.
Parse is deep, and hard to describe in prose/text, because the behavior and data mixture will be verbose. An interactive tool will be much better, so you can see what rule is being evaluated, the current location in the input, and maybe hints about keyword behavior. e.g. if
ahead is evaluated, a "does not advance" indicator could light up.
There was an old parsing tool, VisualParse++, from Sandstone technology, that did something like that. It was a shift-reduce parsing tool, and was pretty cool.
I'm new to the language and I'm trying to do something that I think is quite simple, but I fail.
I just want to convert a hexadecimal byte that is on string format to a binary value.
Something that works:
t: #"^(AB)" a: to binary! to-hex/size (to integer! t) 2 print a
I now want to "construct" t so that "AB" can be a string, ie construct a character from a string if that makes any sense.
I know that are other ways to do this but this got interesting.
construct a character from a string
A string is composed of characters, so such wording doesn't make much sense in this context. You might want to extract a character from a string rather.
>> t: "12345" == "12345" >> repeat a length? t [ print t/a ] *** Script Error: word! type is not allowed here *** Where: print *** Stack: >> repeat a length? t [ print t/(a) ] 1 2 3 4 5 >>
a, but inside parens
ais first evaluated to number and only then path is accessed. String is series, and you can access its elements by index numbers but not by literal words. Other structures can be accessed by words, e.g.:
>> t: [a b c] == [a b c] >> t/a == b >> t: #(a: 1 b: 2) == #( a: 1 b: 2 ) >> t/a == 1 >> t: object [a: 1 b: 2] == make object! [ a: 1 b: 2 ] >> t/a == 1