phrase/3 — The Logtalk Handbook v3.47.0 documentation

# `phrase/3`

## Description

    phrase(GrammarRuleBody, Input, Rest)
    phrase(::GrammarRuleBody, Input, Rest)
    phrase(Object::GrammarRuleBody, Input, Rest)

True when the `GrammarRuleBody` grammar rule body can be applied to the `Input-Rest` difference list of tokens. In the most common case, `GrammarRuleBody` is a non-terminal defined by a grammar rule. This built-in method is declared private and thus cannot be used as a message to an object. When using a backend Prolog compiler supporting a module system, calls in the format `phrase(Module:GrammarRuleBody, Input, Rest)` may also be used.

This method is opaque to cuts in the first argument. When the first argument is sufficiently instantiated at compile time, the method call is compiled in order to eliminate the implicit overheads of converting the grammar rule body into a goal and meta-calling it. For performance reasons, the second and third arguments are only type-checked at compile time.

## Modes and number of proofs

    phrase(+callable, ?list, ?list) - zero_or_more

## Errors

`NonTerminal` is a variable:
`instantiation_error`
`NonTerminal` is neither a variable nor a callable term:
`type_error(callable, NonTerminal)`

## Examples

To parse a list of tokens using a local non-terminal:
`phrase(NonTerminal, Input, Rest)`
To parse a list of tokens using a non-terminal within the scope of self:
`phrase(::NonTerminal, Input, Rest)`
To parse a list of tokens using a public non-terminal of an explicit object:
`phrase(Object::NonTerminal, Input, Rest)`

See also

call//1-N, phrase/2, phrase/3