pLabel

fun <I : Any, O, U : Any> pLabel(parser: Parser<I, O, U>, message: String): Parser<I, O, U>

Returns a Parser that runs parser and, if it fails, replaces the failure message with message.

pLabel is the primary way to produce human-readable error messages. Instead of exposing low-level diagnostic text from pSatisfy or nested combinators, wrap a parser in pLabel to emit a single, intent-describing message when it fails.

On success the result is passed through unchanged.

Behaviour

Condition	Result
parser succeeds	Success propagated unchanged
parser fails	Failure with message; index and input from the original failure

Type parameters

I — the token type consumed by parser.
O — the output type of parser.
U — the user context type threaded through unchanged.

Example

val digit = pLabel(pSatisfy<Char, Unit> { it.isDigit() }, "a digit")

val input = ParserInput.of("abc".toList(), Unit)
val result = digit(input)
// Failure("a digit", index=0, ...)

Return

a Parser that propagates success and replaces failure messages.

Parameters

parser

the parser to run.

message

the failure message to use when parser fails.