How to parse a string literal

[lambdakris]

Description

Referring to Parsing Routes in the docs, I was not able to parse a string literal.

Repro code

open Elmish.Browser.UrlParser

parse (s "blog") "blog"

Expected and actual result

I figured it would compile and yield Some "blog", however, the expression doesn't compile due to the following error:

Type mismatch. Expecting a 
  'Parser<('a -> 'a)>, 'a>'
but given a
  'Parser<('a -> 'a), ('a -> 'a)>'
the types ''a' and ''a -> 'a' cannot be unified

Related information

• fable-elmish version: 0.9.2
• fable-compiler version: 1.1.9
• fable-core version: 1.1.7
• Operating system: Windows 10

[et1975]

s "blog" in your example refers to a "static" portion - something that is expected to be present in the input, but is not captured, ie the parser as specified has no instructions to extract something and I guess the compiler can't infer the types involved.
parse str "blog" would do what you expect it to do.

[lambdakris]

I was actually looking into how to get something like the following:

type Route = Home | Search of string
let routes = 
    [ map Home (s "home")
      map Search (s "search" </> str) ]
parse (oneOf routes)

or just

parse (map Home (s "home"))

Which works, but I was just hoping there was a way to build a "match a string" expression without applying the map function...

[et1975]

The idea of this parser-combinator module is that a single type unifies the parsed out values, what you are asking for can only be represented by a DU, so you need to pass the map function to construct it.