Argon

Argon measures your code's cyclomatic complexity.

---

Installing

Simple as cabal install argon.

GHC compatibility

Argon parses Haskell using the standalone ghc-lib-parser, so it is independent of the compiler used to build it. It builds with modern GHC (tested with GHC 9.10) and understands the Haskell syntax of its pinned ghc-lib-parser (currently the 9.12 series). Older argon releases targeting GHC 7.8–8.x can be found on the releases page.

About the complexity being measured

argon will compute the cyclomatic complexity of Haskell functions, which is the number of decisions in a block of code plus 1. For instance the following function:

func n = case n of
           2 -> 3
           4 -> 6
           _ -> 42

has a cyclomatic complexity of 3.

The boolean operators && and || also affect the this number. For instance the following function:

g n = n < 68 && n `mod` 3 == 2 && n > 49

has a cyclomatic complexity of 3.

As a last example, the following function:

func n = case n of
           2 -> 3
           4 -> 6
           _ -> if 0 < n
                then 7
                else 8

has a cyclomatic complexity of 5.

Cyclomatic complexity provides a very shallow metric of code complexity: a high cyclomatic complexity number does not necessarily mean that the function is complex, and conversely, a low number does not necessarily indicate that the function is simple. However, this number it can be useful for highlighting potential maintainability issues.

Running

The Argon executable expects a list of file paths (files or directories):

$ argon --no-color --min 2 src
src/Argon/Formatters.hs
    42:1 coloredFunc - 2
    43:11 color - 2
    57:1 formatResult - 2
src/Argon/SYB/Utils.hs
    20:1 everythingStaged - 2
src/Argon/Preprocess.hs
    34:1 toCpphsOptions - 2
    44:5 parseDefine - 2
src/Argon/Loc.hs
    20:11 toRealSrcLoc - 2
src/Argon/Walker.hs
    22:1 walk - 4
    15:1 allFiles - 2
src/Argon/Results.hs
    46:1 filterNulls - 3
    66:1 exportStream - 3
    56:1 filterResults - 2
src/Argon/Parser.hs
    67:1 parseModuleWithCpp - 3
    42:1 analyze - 2
    46:9 analysis - 2
    105:1 renderError - 2
src/Argon/Cabal.hs
    23:11 toString - 3
src/Argon/Types.hs
    81:5 toJSON - 2
src/Argon/Visitor.hs
    61:1 visitExp - 6
    71:1 visitOp - 4
    30:11 visit - 2

For every file, Argon sorts results with the following criteria (and in this order):

1. complexity (descending)
2. line number (ascending)
3. alphabetically

When colors are enabled (default), Argon computes a rank associated with the complexity score:

JSON

Results can also be exported to JSON:

$ argon --json --min 2 src
[
  {
    "blocks": [
      { "col": 1, "complexity": 2, "lineno": 42, "name": "coloredFunc" },
      { "col": 11, "complexity": 2, "lineno": 43, "name": "color" },
      { "col": 1, "complexity": 2, "lineno": 57, "name": "formatResult" }
    ],
    "path": "src/Argon/Formatters.hs",
    "type": "result"
  },
  {
    "blocks": [{ "col": 1, "complexity": 2, "lineno": 20, "name": "everythingStaged" }],
    "path": "src/Argon/SYB/Utils.hs",
    "type": "result"
  },
  {
    "blocks": [
      { "col": 1, "complexity": 2, "lineno": 34, "name": "toCpphsOptions" },
      { "col": 5, "complexity": 2, "lineno": 44, "name": "parseDefine" }
    ],
    "path": "src/Argon/Preprocess.hs",
    "type": "result"
  },
  {
    "blocks": [{ "col": 11, "complexity": 2, "lineno": 20, "name": "toRealSrcLoc" }],
    "path": "src/Argon/Loc.hs",
    "type": "result"
  },
  {
    "blocks": [
      { "col": 1, "complexity": 4, "lineno": 22, "name": "walk" },
      { "col": 1, "complexity": 2, "lineno": 15, "name": "allFiles" }
    ],
    "path": "src/Argon/Walker.hs",
    "type": "result"
  },
  {
    "blocks": [
      { "col": 1, "complexity": 3, "lineno": 46, "name": "filterNulls" },
      { "col": 1, "complexity": 3, "lineno": 66, "name": "exportStream" },
      { "col": 1, "complexity": 2, "lineno": 56, "name": "filterResults" }
    ],
    "path": "src/Argon/Results.hs",
    "type": "result"
  },
  {
    "blocks": [
      { "col": 1, "complexity": 3, "lineno": 67, "name": "parseModuleWithCpp" },
      { "col": 1, "complexity": 2, "lineno": 42, "name": "analyze" },
      { "col": 9, "complexity": 2, "lineno": 46, "name": "analysis" },
      { "col": 1, "complexity": 2, "lineno": 105, "name": "renderError" }
    ],
    "path": "src/Argon/Parser.hs",
    "type": "result"
  },
  {
    "blocks": [{ "col": 11, "complexity": 3, "lineno": 23, "name": "toString" }],
    "path": "src/Argon/Cabal.hs",
    "type": "result"
  },
  {
    "blocks": [{ "col": 5, "complexity": 2, "lineno": 81, "name": "toJSON" }],
    "path": "src/Argon/Types.hs",
    "type": "result"
  },
  {
    "blocks": [
      { "col": 1, "complexity": 6, "lineno": 61, "name": "visitExp" },
      { "col": 1, "complexity": 4, "lineno": 71, "name": "visitOp" },
      { "col": 11, "complexity": 2, "lineno": 30, "name": "visit" }
    ],
    "path": "src/Argon/Visitor.hs",
    "type": "result"
  }
]