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PPX rewriter for HardCaml

This module provides a PPX rewriter for some of HardCaml syntax:

  • Enable the use of pervasive operator names to manipulate signals
  • Reuse the 2D string indexing syntax for signal indexing

Examples

Operators

Original syntax:

let some_function a b =
  a &: b

Using the PPX rewriter:

let some_function a b =
  [%hw a land b]

Using the let% extension of the PPX rewriter:

let some_function a b =
  let%hw result = a land b in
  result

Signal in binary operations are also automatically resized using uresize to max a b.

Indexing

Original syntax:

let some_function a =
  a.[7:0]

Using the PPX rewriter:

let some_function a =
  [%hw a.[7,0]]

Using the expression let% extension of the PPX rewriter:

let some_function a =
  let%hw result = a.[7,0] in
  result

Using the structural let% extension of the PPX rewriter:

let%hw some_function a =
  a.[7,0]

If expression

The if operator needs to bear the hw attribute regardless of its scope:

let%hw select_const sel1 sel2 a b c d =
  if sel1 then
    if%hw sel2 then (a+b) else (a-b)
  else
    if%hw sel2 then (c+d) else (c-d)

Match expression

The match operator needs to bear the hw attribute regardless of its scope:

let%hw simple_match v = 
  let f x = 
    match%hw x with
    | 1 -> 10h
    | 7 -> 77h
    | _ -> 100h
  in
  f v

Hardware constants

Hardware constants can be built using the h integer constant suffix: 0x17h, 32h, 0b0001000h.

Signed operations

Signed operations are accessible through the [%hw.signed] extension.

Implementation details

  • The [%hw] extension is recursively applied to function calls, tuples, and lists
  • When using the expression let%hw syntax, the extension is only applied to the value-binding part of the expression
  • When using the structural let%hw syntax, the extension is recursively applied to all expressions