Alex D

module sum_example ;

import std.stdio ;
import std.conv ;
import ast_parser ;

string indent (int n)
{
    string indent_str = "    " ;
    string result = "" ;
    foreach (i ; 0 .. n)
        result ~= indent_str ;
    return result ;
}

string sumImpl (string astStr)
{
    string AST_ERROR_STR = "Sum AST error : incorrect sum syntax" ;
    string loop_var   [] ;
    string loop_start [] ;
    string loop_end   [] ;
    string loop_inc   [] ;
    string loop_cond  [] ;
    string loop_body ;

    auto ast = TokenList.parseD (astStr) ;
    assert (ast.length >= 3, AST_ERROR_STR) ;
    assert (ast.getStringItem (0) == ";", "Sum AST error : sum must be separeted by semicolons") ;

    foreach (i ; 1 .. ast.length - 1)
    {
        auto arg = ast.getItem (i) ;
        TokenList ast_cycle ;
        if (arg.getStringItem (0) == ",")
        {
            ast_cycle = arg.getItem (1) ;
            loop_cond ~= arg.getItem (2).toD_String () ;
        }
        else
        {
            loop_cond ~= null ;
            ast_cycle = arg ;
        }
        assert (ast_cycle.getStringItem (0) == "=", AST_ERROR_STR) ;
        loop_var ~= ast_cycle.getStringItem (1) ;

        // (: 1 1 10)
        // (: 1 10)
        ast_cycle = ast_cycle.getItem (2) ;
        assert (ast_cycle.getStringItem (0) == ":", AST_ERROR_STR) ;
        loop_start ~= ast_cycle.getItem (1).toD_String () ;
        if (ast_cycle.length == 4)
        {
            loop_inc ~= ast_cycle.getItem (2).toD_String () ;
            loop_end ~= ast_cycle.getItem (3).toD_String () ;
        }
        else
        if (ast_cycle.length == 3)
        {
            loop_inc ~= null ;
            loop_end ~= ast_cycle.getItem (2).toD_String () ;
        }
        else
            assert (0, AST_ERROR_STR) ;
    }
    loop_body = ast.getItem (ast.length - 1).toD_String () ;

    auto sum_i = new string [ast.length - 2] ;
    string result = "function int () {\n" ;
    int idt = 1 ;
    foreach (i ; 0 .. ast.length - 2)
    {
        sum_i [i] = "sum_" ~ to!string (i) ;
        result ~=
indent (idt) ~ "int " ~ sum_i [i] ~ " ;\n" ~
indent (idt) ~ "for (int " ~ loop_var [i] ~ " = " ~ loop_start [i] ~ " ; " ~ loop_var [i] ~ " < " ~ loop_end [i] ~ " ; " ;

        if (loop_inc [i] is null)
            result ~= "++" ~ loop_var [i] ;
        else
            result ~= loop_var [i] ~ " += " ~ loop_inc [i] ;

        result ~= " )\n" ~
            indent (idt) ~ "{\n" ;

        if (loop_cond [i] !is null)
        {
            ++ idt ;
            result ~= indent (idt) ~ loop_cond [i] ~ "\n"
                ~ indent (idt) ~ "{\n";
        }

        if (i == ast.length - 3)
        {
            result ~= indent (idt + 1) ~ sum_i [i] ~ " += " ~ loop_body ~ " ;\n" ;
            if (loop_cond [i] !is null)
            {
                result ~= indent (idt) ~ "}\n" ;
                -- idt ;
            }
            result ~= indent (idt) ~ "}\n" ;
        }
        else
            ++ idt ;
    }
    foreach_reverse (i ; 0 .. ast.length - 3)
    {
        string res = indent (idt) ~ sum_i [i] ~ " += " ~ sum_i [i+1] ~ " ;\n" ;
        if (loop_cond [i] !is null)
        {
            result ~= res ;
            -- idt ;
            result ~= indent (idt) ~ "}\n" ;
        }
        else
            result ~= res ;
        -- idt ;
        result ~= indent (idt) ~ "}\n" ;
    }

    result ~= indent (1) ~ "return sum_0 ;\n"
        ~ "} ()" ;
    return result ;
}

string sumImpl2 (string loop_var, string loop_start, string loop_end, string loop_body)
{
    return
"function int () {\n" ~
"int sum_ ;\n" ~
"foreach ( " ~ loop_var ~ " ; " ~ loop_start ~ " .. "  ~ loop_end ~ " )\n" ~
"{\n" ~
"    sum_ += " ~ loop_body ~ " ;\n" ~
"}\n" ~
"return sum_ ;\n" ~
"} ()" ;
}

template sum (string loop_var, string loop_start, string loop_end, string loop_body)
{
    mixin ("enum sum = " ~ sumImpl2 (loop_var, loop_start, loop_end, loop_body)  ~ " ;") ;
}

template sum2 (string s)
{
    mixin ("enum sum2  = " ~ s ~ ";") ;
}

void main ()
{
    int x = sum2 !(q{1 + sum2!("2")}) ;
    writeln (x) ;
    x = 1 + sum! ("i", "1", "10", q{i * sum!("j", "0", "9", "1+j")}) ;
    writeln (x) ;

    writeln (sumImpl ("i = 1:10 ; j = 1:2:n+1, if (j != i) ; k = i:j, if (k != 3) ;  i*i/(k+j^3) + 2")) ;
}