Back testing in Q

I get this all the time- how do you backtest a strategy.
Well, here's a simple way. Every trade has 4 components- it's entry time, it's profit objective (ge: good exit)) it's stop limit (se- stop exit) and a time exit (te).
The code below will, given a table with a column "entry" which is boolean and a price will backtest the strategy (this is a version for going long). I like to back test against quotes, but this is for prices (trades).




btL:{[t;gep;sep;tep]
i_eb:where t`entry; //where are the entry indicies
i_te:(count t)^((t`time) bin/: ((t@i_eb)`time)+tep*1000); //find the indicies for the time exits
rng:{x+key floor (y-x)}'[i_eb;i_te]; //define the ranges
f_u:{[xe;limit;p;x]limit&x+xe>p x};f_l:{[xe;limit;p;x]limit&x+xe<p x}; //functions for upper and lower limits
e_pr:(t`entryprice)i_eb; //define the entry prices
i_ge:f_u[(e_pr+gep);i_te;t`bid1]/[i_eb]; //indices for the good exits
i_se:f_l[(e_pr-sep);i_te;t`bid1]/[i_eb]; //indices for the stop exits
i_xe:min each v:(count t)^flip (i_te;i_ge;i_se); //define the exit action
x_ty:(`te`ge`se)@/:i_x:first each iasc each v; //define the exit types
x_pr:(t`bid1) i_xe; //the exit price is the bid at the exit index
x_pl:x_pr-(e_pr); //the exit pnl is the exit price- entry price
`entrytime`exittime`entryprice`exittype`exitprice`exitindx`pnl!((t`time)i_eb;(t`time)i_xe;e_pr;x_ty;x_pr;i_xe;x_pl)}





An example

n:1000;
t:`time xasc flip `time`price`entry`entryprice!(n?`time$.z.Z;n?10;n?01b;n?10)
btL[t;2;1;30] //go for 2$,risk 1$, hold for 30 seconds