A Template includes an ordered list of placeholders and text segments. Templates guarantee that

List.length segments == List.length placeholders + 1

and they can be converted back to the same String representation they were parsed from.

Parse a String into a Template based on a Syntax.

syntax : Syntax
syntax = { startSymbol = "${", endSymbol = "}" }


parseTemplate syntax "This is ${name}s example" |> Result.map (always ())


--> Ok ()
parseTemplate syntax "This does not ${makeSense"


--> Err "TODO deadEndsToString" -- (Waiting for upstream fix in elm/parser)

Get the names of the placeholders in a Template.

parseTemplate { startSymbol = "${", endSymbol = "}" } "${first} ${snd}"
    |> Result.map getPlaceholderNames
--> Ok ["first", "snd"]

Convert a parsed Template back to its String representation. For any template built with Syntax s,

templateToString >> parseTemplate s == identity


parseTemplate { startSymbol = "${", endSymbol = "}" } "This is ${name}s example"
    |> Result.map templateToString
--> Ok "This is ${name}s example"

A Syntax tells the templateParser how to distinguish placeholders from regular text. At the moment, this can only be configured by setting start and end symbol.

Parse a String into a function substituting the argument at the position marked by the Syntax.

exampleOf : Result String (String -> String)
exampleOf = parsePlaceholder1 { startSymbol = "${", endSymbol = "}" } "This is ${name}s example"


Result.map ((|>) "Andy") exampleOf
--> Ok "This is Andys example"


parsePlaceholder1 { startSymbol = "${", endSymbol = "}" } "No placeholder"
--> Err "Expected more placeholders."


parsePlaceholder1 { startSymbol = "${", endSymbol = "}" } "${multiple}${placeholders}"
--> Err "Expected less placeholders."

Parse a String into a function substituting the arguments at the two positions marked by the Syntax.

parsePlaceholder2 { startSymbol = "{", endSymbol = "}" } "{greeting} {target}"
    |> Result.map (\f -> f "Hello" "World")
--> Ok "Hello World"

Parse a String into a function substituting the arguments at the three positions marked by the Syntax.

Parse a String into a function substituting the arguments at the four positions marked by the Syntax.