Re: How can i understand the code below

[Laura]

A lot to unpack here but lets break it down.

.quantQ.IO.SAVEsPLAYtAB:{[tabPath;pvar;table]   // tabPath -- path where to store the table   // pvar -- variable to sort and index on for fast querying   // table -- name of the table to save   @[;pvar;`p#] pvar xasc (`sv (tabPath; ` ; table; `)) set .Q.en[tabPath] get table}

The three arguments are all symbols: respectively a file path, a table column name, and a table name. (It were best to state that in the comments.) Ill come to how we see that.

Lets set up a small table so we can watch what happens.

q)atable:([]ab:til 3;cd:`x`y`z;de:string`tom`**bleep**`harry) q)get `atable ab cd de ------------- 0 x "tom" 1 y "**bleep**" 2 z "harry" q)tabPath:`:path/to/table

The argument to get is the name of the table; the result is the table, which becomes the argument to .Q.en[tabPath].

That is, binary .Q.en is projected onto tabPath to make a unary. The effect is the same as if we had assigned the result of get table to t and then called .Q.en[tabPath;t]. What .Q.en does is too extensive to discuss here but you can read up on it. The work it does is side effects; its result is the table.

Which then gets passed as the right argument to set, which is quite a workhorse. Its syntax is overloaded, so we examine its left argument (` sv (tabPath; ` ; table; ` ) ) to see how set is used here.

The sv keyword is being called in this form, which is how we know that tabPath and table must both be symbols. It returns a filehandle symbol as the left argument of set.

From this we see that set is being called with syntax til set y // serialize y to fil. It returns its left argument: the symbol filepath to which it has written the table; this becomes the right argument to xasc, which will sort the table on disc by the column named by pvar.

The result is again a reference to the table, which becomes the argument to @[;pvar;`p#], a projection of Apply At onto second and third arguments pvar and `p#. The effect is to set the partitioned attribute on the column named by pvar. The result of Apply At is the table reference. Your code uses Explicit return : to make that the result of .quantQ.IO.SAVEsPLAYtAB. That is unnecessary: a functions result is the result of evaluating its last (here the single) expression.