Random notes about tagging Elm source code with Universal Ctags

Manual group:Universal Ctags
Manual section:7


ctags … --languages=+Elm …
ctags … --language-force=Elm …
ctags … --map-Elm=+.elm …


The Elm parser is a PEG parser using PackCC, which is part of the ctags infrastructure. It should correctly process all top level statements, however there is a limitation with functions embedded in let/in blocks. They will mostly be fine, but sometimes a function in a let/in block will be omitted.



Imported modules are tagged, and their role is “imported”, not “def”. Types, functions, etc which are exposed via imported module have their role as “exposed”.

Exposed items are marked as being in the scope of their own module, not the module that’s doing the importing.


module SomeMod exposing (..)

import MyMod exposing
  ( map
  , Maybe
  , Result(..)
  , MyList(Empty)

“output.tags” with “--options=NONE -o - --sort=no --extras=+r --fields=+r input.elm”

SomeMod input.elm       /^module SomeMod exposing (..)$/;"      m       roles:def
MyMod   input.elm       /^import MyMod exposing$/;"     m       roles:imported
map     input.elm       /^  ( map$/;"   f       module:MyMod    roles:exposed
Maybe   input.elm       /^  , Maybe$/;" t       module:MyMod    roles:exposed
Result  input.elm       /^  , Result(..)$/;"    t       module:MyMod    roles:exposed
MyList  input.elm       /^  , MyList(Empty)$/;" t       module:MyMod    roles:exposed
Empty   input.elm       /^  , MyList(Empty)$/;" c       type:MyMod.MyList       roles:exposed


Namespaces are tagged and their role is “def”.


module AMod exposing (..)

import MyImport as NSpace exposing (impFunc)

“output.tags” with “--options=NONE -o - --sort=no --extras=+r --fields=+r input.elm”

AMod    input.elm       /^module AMod exposing (..)$/;" m       roles:def
NSpace  input.elm       /^import MyImport as NSpace exposing (impFunc)$/;"      n       module:AMod     roles:def       moduleName:MyImport
MyImport        input.elm       /^import MyImport as NSpace exposing (impFunc)$/;"      m       roles:imported
impFunc input.elm       /^import MyImport as NSpace exposing (impFunc)$/;"      f       module:MyImport roles:exposed

Type names

Constructors top level functions will have type names.


funcA : Int -> Int
funcA a = a + 1

type B
    = B1Cons
      { x : Float
      , y : Float
    | B2Cons String Integer
    | B3Cons

“output.tags” with “--options=NONE -o - --sort=no --extras=+r --fields=+r input.elm”

funcA   input.elm       /^funcA a = a + 1$/;"   f       typeref:typename:Int -> Int     roles:def
B       input.elm       /^type B$/;"    t       roles:def
B1Cons  input.elm       /^    = B1Cons$/;"      c       type:B  typeref:typename:{ x : Float , y : Float } -> B roles:def
B2Cons  input.elm       /^    | B2Cons String Integer$/;"       c       type:B  typeref:typename:String -> Integer -> B roles:def
B3Cons  input.elm       /^    | B3Cons$/;"      c       type:B  typeref:typename:B      roles:def

Function parameter lists

Function parameter lists can be extracted into the tags file signature field. They are not really function signatures, but it’s the closest concept available in ctags. Use “--fields=+S”.

funcA a1 a2 =
    a1 + a2

“output.tags” with “--sort=no --extras=+r --fields=+rS”

funcA       input.elm       /^funcA a1 a2 =$/;"     f       signature:a1 a2 roles:def


The ctags signature field is used for function parameter lists, even though it’s not an idea field. See above.

Elm requires all statements at the same logical level to have the same indentation. If there is additional indentation that line is part of the previous one. Therefore without over-complicating the PEG parser we have the following limitations…

Sometimes functions in let/in blocks will be omitted.

Functions in let/in blocks will be marked as being in the scope of their outer function, regardless of how deeply nested the let/in block is.

Functions in let/in blocks won’t have type names.