Compile time lex + parse + semantic = 300 lines of code

[Regan Heath]

Daniel Keep wrote:
> 
> Don Clugston wrote:
>> I've finally released the compile-time parser I mentioned in my
>> conference presentation.
>>
>> http://www.dsource.org/projects/mathextra/browser/trunk/blade/SyntaxTree.d
>>
>> contains one publicly usable function:
>>
>> char [] syntaxtreeof(char [] expression).
>>
>> When mixed in, this lexes and parses the expression, determines
>> precedence and associativity, creating an object of type
>> AbstractSyntaxTree, which contains a standardized 'placeholder
>> expression' (eg "A+=(B*C)")
>> and a symbol table for the variables, constants and functions A,B,C,...
>> The symbol table includes the type and value for each symbol.
>> All aliases and compile-time constants are resolved and converted to a
>> standard form.
>> All symbols must be reachable from the scope where syntaxtreeof() is
>> mixed into.
>>
>> The created AbstractSyntaxTree is a compile-time constant, so it can be
>> used for  further compile-time operations and code generation.
>>
>> Works for almost any expression (templates, functions, strings, slicing,
>> struct literals,...); the biggest omission is relational operators.
>> Less than 300 lines of code in D1.020.
>> Probably could simplified using __traits in D2.0.
>> Enjoy.
>>
>>
>> Return type:
>> -----
>> struct Symbol {
>>     char [] type; // the name of the type, as text
>>     char [] value; // the value, as text. Either the symbol name, or a
>> literal
>> }
>>
>> // The result of semantic analysis of the original expression
>> struct AbstractSyntaxTree {
>>     char [] expression; // syntax tree in Placeholder format, eg A+=(B*C)
>>     Symbol[] symbolTable; // The types and values of A,B,C,...
>> }
>> ------
>>
>> Example:
>> -----
>> import SyntaxTree;
>>
>> const foo = "abc";
>> int bar(real x, char [] s) { return 0; }
>> struct Duck{};
>> Duck duck;
>>
>> AbstractSyntaxTree a = mixin(syntaxtreeof(`foo*   bar(2.18_3242e+45L,
>> "xyz") in duck`));
> 
> Words fail me; I'm going to have to borrow some from Dave Grossman:
> 
> Sweet mother of double-jeopardy back-stroking in butterscotch with a
> holy cap-wearing catfish flopping a crime-beat past sweet suffering St.
> Sebastian on a sousaphone in a short story by Susan Sontag with the
> great grinning head of John the Baptist in a pork-pie hat stuffed in a
> rhinestone bowling bag by the Greek goddess Celine in a chariot with
> dual overhead cams and Silver Fox mudflaps...
> 
> ...that's impressive.

This is the sort of thing that needs to be published in a "Check out the 
crazy sh!t we can do with D" article :D

Regan