7.4 Definition Macros🔗ℹ

A compile-time value that identifies the same space as defn. See also SpaceMeta.

The expansion result must be a sequence of groups that are inlined in place of the definition-macro use.

The options in the macro body must be distinct; since there is only one option currently, either the ~op_stx option is present or not. The ~op_stx option, if present, binds an identifier for a use of the macro (which cannot be matched directly in the pattern, since that position is used for the name that defn.macro binds).

Using | alternatives, a single definition can have any number of patterns, which are tried in order. The defined_name must be the same across all cases.

> defn.macro 'enum:                 $lhs                 ...':     let [n, ...] = List.iota([lhs, ...].length())     'def $lhs = $n      ...'

> enum:     a     b     c

> b

1

The macro result is two values: a sequence of groups to splice in place of the sequence-macro use, and a sequence of groups that represent the tail of the definition context that was not consumed.

> defn.sequence_macro 'reverse_defns                        $defn1                        $defn2                        $tail                        ...':     values('$defn2; $defn1', '$tail; ...')

> reverse_defns   def seq_x = seq_y+1   def seq_y = 10   seq_x

11

Syntax class that matches only groups that start with an identifier that is bound as a definition form.

Unlike expr_meta.Parsed, defn_meta.Group does not parse the definition form, because the form normally needs to be parsed within a definition context. This syntax class can be used to distinguish definitions from other forms that need to be treated differently in some context.

Syntax class that matches only groups that starts with an identifier that is bound as a definition-sequence form.

Similar to expr_meta.pack_s_exp, but for definitions.