package tyxml-syntax

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Attribute value parsers and parser combinators.

type 'a gparser = ?separated_by:string -> ?default:string -> Ppxlib.Location.t -> string -> 'a -> Ppxlib.expression option
type parser = string gparser
type vparser = string Common.value gparser

Attribute value parsers are assigned to each attribute depending on the type of the attribute's argument, though some attributes have special parsers based on their name, or on a [@@reflect] annotation. A parser is a function p such that p loc name value either:

  • converts the string value into Some of a parse tree representing that value, for use with attributes that take an argument, or
  • evaluates to None, for use with attributes that take no argument (for instance, a_selected).

For example, int loc name "3" converts "3" into the parse tree {pexp_desc = Pexp_constant (Const_int 3); ...}.

The parse tree is assigned the location loc. This should be the location of the start of the value string, but, presently, the location of the element containing the value string is used.

name is the name of the attribute. This is used only for error reporting.

~separated_by and ~default are used internally by combinators to modify the error message (for example, to make nouns plural if an error occurs in a list).

Combinators

val option : string -> parser -> parser

option none parser _ _ s behaves as follows:

  • if s = none, evaluates to a parse tree for None.
  • otherwise, if parser _ _ s evaluates to a parse tree for e, option evaluates to a parse tree for Some e.
val spaces : parser -> parser

spaces parser _ _ s splits s on spaces, then applies parser to each component. The resulting parse trees for e, e', ... are combined into a parse tree of [e; e'; ...].

val commas : parser -> parser

Similar to spaces, but splits on commas.

val semicolons : parser -> parser

Similar to spaces, but splits on semicolons.

val spaces_or_commas : parser -> parser

Similar to spaces, but splits on both spaces and commas.

Top combinators

Exported parsers should always use one of those combinators last.

val wrap : parser -> Common.lang -> vparser

wrap parser module_ _ _ s applies parser _ _ s to get a parse tree for e, then evaluates to the parse tree for module_.Xml.W.return e.

val nowrap : parser -> Common.lang -> vparser

nowrap parser _ _ _ s evaluates to parser _ _ s. The purpose of this combinator is to provide a signature similar to wrap in situations where wrapping is not wanted.

Numeric

val char : parser

char _ _ s, where s is a string containing a single UTF-8 character c, produces a parse tree for c of type char. Note that this means the range is restricted to the first 256 code points.

val bool : parser

bool _ _ s produces a parse tree for the boolean true if s = "true" or "" and false if s = "false".

val onoff : parser

onoff _ _ s produces a parse tree for the boolean true if s = "on" or "" and false if s = "off".

val unit : parser

unit _ name s produces a parse tree for (). It fails if name <> s.

val int : parser

int _ _ s produces a parse tree for int_of_string s.

val float : parser

float _ _ s produces a parse tree for float_of_string s. This is a slight superset of HTML and SVG decimal fraction number syntax.

val points : parser

Similar to spaces_or_commas float, but pairs consecutive numbers.

val number_pair : parser

number_pair _ _ s produces a parse tree for

  • n, None if s = (string_of_float n), or
  • m, Some n' if s is a space- or comma-separated list of representations of two floats.
val fourfloats : parser

Acts as spaces_or_commas float, but expects the list to have exactly four elements.

val icon_size : parser

icon_size _ _ s produces a parse tree for the pair (width, height) when s has the form (string_of_int width) ^ x ^ (string_of_int height) and x is either "x" or "X".

Dimensional

val svg_length : parser

svg_length _ _ s produces a parse tree for a value of type Svg_types.Unit.(length quantity). s is expected to have form (string_of_float n) ^ unit for some number n and a valid SVG length unit, or no unit.

val angle : parser

Similar to svg_length, but for SVG angles.

val offset : parser

offset _ _ s produces a parse tree for

  • `Number n if s = string_of_float n, or
  • `Percentage n if s has form (string_of_float n) ^ "%".
val transform : parser

Parses an SVG transform attribute value.

val string : parser

string _ _ s produces a parse tree for s. This is intended for ordinary attributes containing text that requires no further parsing.

val variant : parser

variant _ _ s produces a parse tree for the variand Tyxml_name.polyvar s. This is intended for attributes whose argument type is a polymorphic variant, none of whose constructors take arguments.

val total_variant : (string * string list) -> parser

total_variant is used for parsing arguments whose type is a variant with the following pattern:

| `A | `B | `C | `EverythingElse of string

It behaves like variant for strings matching the no-argument constructors. Any other string s is mapped to the parse trees for `EverythingElse s.

val variant_or_empty : string -> parser

variant_or_empty empty is used for parsing arguments whose type is a variant, possibly the empty string. It behaves like variant for every string but the empty one, which will be parsed as if it was the empty parameter.

val presence : parser

presence _ _ _ evaluates to None. It is used as a "parser" for attributes that do not take arguments.

val paint : parser
val srcset_element : parser

Used for a_srcset.

val number_or_datetime : parser

Used for a_input_min and a_input_max.

val sandbox : parser
val in_ : parser
val in2 : parser
val xmlns : parser