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--- An intelligent 'loop-unrolling' macro.
-- `do_` defines a named scoped macro `var` which is the loop iterator.
--
-- For example,
--
-- y = 0
-- do_(i,1,10
-- y = y + i
-- )
-- assert(y == 55)
--
-- `tuple` is an example of how the expansion of a macro can be
-- controlled by its context. Normally a tuple `A` expands to
-- `A_1,A_2,A_3` but inside `do_` it works element-wise:
--
-- tuple(3) A,B
-- def_ do3(stmt) do_(k,1,3,stmt)
-- do3(A = B/2)
--
-- This expands as
--
-- A_1 = B_1/2
-- A_2 = B_2/2
-- A_3 = B_3/2
--
-- @module macro.do
local M = require 'macro'
--- Expand a loop inline.
-- @p var the loop variable
-- @p start initial value of `var`
-- @p finish final value of `var`
-- @p stat the statement containing `var`
-- @macro do_
M.define('do_(v,s,f,stat)',function(var,start,finish,statements)
-- macros with specified formal args have to make their own putter,
-- and convert the actual arguments to the type they expect.
local put = M.Putter()
var,start,finish = var:get_iden(),start:get_number(),finish:get_number()
M.push_macro_stack('do_',var)
-- 'do_' works by setting the variable macro for each value
for i = start, finish do
put:name 'set_':name(var):number(i):space()
put:tokens(statements)
end
put:name 'undef_':name(var)
put:name '_DROP_':string 'do_':space()
return put
end)
--- an example of conditional expansion.
-- `tuple` takes a list of variable names, like a declaration list except that it
-- must end with a line end.
-- @macro tuple
M.define('tuple',function(get)
get:expecting '('
local N = get:number()
get:expecting ')'
local names = get:names '\n'
for _,name in ipairs(names) do
M.define(name,function(get,put)
local loop_var = M.value_of_macro_stack 'do_'
if loop_var then
local loop_idx = tonumber(M.get_macro_value(loop_var))
return put:name (name..'_'..loop_idx)
else
local out = {}
for i = 1,N do
out[i] = name..'_'..i
end
return put:names(out)
end
end)
end
end)
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