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

[Daniel Keep]

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.

	-- Daniel