Macros can be used to define new tags and to build abstraction with procedures in style files.

Operator Arity Accessible Process Usage border children macro n + 1 Yes All but last Macro Style arg 1 + n Yes None Macro Style xmacro 2 Yes First Macro Style map-args 3,4,5 Yes None Macro Style eval-args 1 Yes None Functional Style compound 1 + n Yes All but first Macro Style drd-props 1 + 2 (n + 1) Yes None Typesetting Style get-label 1 Yes None Functional Style get-arity 1 Yes None Functional Style action 2,3 Yes First Typesetting Style flag 2 Yes None Typesetting Style

Table 1. Macro primitives

This primitives returns a macro (the TeXmacs analogue of a λ-expression) with n arguments, named after the literal strings var-1 until var-n.

New tags are defined by storing macros in the environment. Most of the time, macros are stored without scope with assign, but it is sometimes useful to redefine a tag locally within the scope of a with. For example, itemized and enumerated environment redefine item locally.

Example 1. Definition of the abbr tag

This primitive is used to retrieve the arguments of a macro within its body. For instance, expands the content of the macro argument with name arg (literal string). Of course, this argument must be defined by a macro containing the arg tag.

This tag is similar to value, but differs in important ways:

• The argument namespace is distinct from the environment, and will generally evaluate to different values (although you should not rely on this).
• The value of arg retains the position of the macro argument in the document tree, that makes it possible to edit the arguments of a macro-defined tag while it is active.

This primitive evaluates to a tree whose root is labeled by root and whose children are the result of applying the macro foo to the children of the macro argument with name var.

By default, the macro foo is applied to all children. If first has been specified, then we rather start at the i-th child of var, where i is the result of evaluating first. If last has been specified to, then we stop at the j-th child of var (the j-th child not being included), where j is the result of evaluating last. In this last case, the arity of the returned tree is therefore j - i.

Stated otherwise, map-args applies foo to all subtrees of the macro argument var (or a range of subtrees if first and last are specified) and collect the result in a tree with label root. In addition, the second argument to foo gives its position of the first argument in the expansion of var.

The map-args is analogue to the Scheme function map. Since TeXmacs use labelled trees, the label of the mapping list must also be specified.

This primitive evaluates to the tree with the same label as the expansion of the argument var and whose subtrees are the result of the evaluation of the subtrees of the expansion of var.

This primitive is useful to expand macros which are the result of a computation: it applies the macro which is the result of the evaluation of foo to the arguments arg-1 until arg-n. The compound primitive is useful in call-back and lambda programming idioms, where a higher-level macro is given a macro as an operand, which it may later apply under certain conditions or with operands which are not known the client code.

Actually, in the current implementation, foo may either evaluate to a macro or to a literal string which gives the name of a macro. However, we discourage users to rely on the second case.

The arity and children accessibility of tags defined by macros are determined heuristically by default. The drd-props primitive overrides this default for the environment variable (usually a macro) with name var. The currently supported property-value pairs are: