diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 42 |
1 files changed, 40 insertions, 2 deletions
@@ -64261,7 +64261,7 @@ through the enumeration is is attempted at run time. .coNP FFI type @ struct .synb -.mets (struct < name >> {( slot << type )}*) +.mets (struct < name >> {( slot << type <> [ init-form ])}*) .syne .desc The FFI @@ -64361,11 +64361,49 @@ to exist, if such a type doesn't already exist. If such a type is created, instance slots are defined for it which correspond to the member definitions in the FFI .code struct -definition. Those members whose +definition. + +For any +.meta slot +which specifies an +.meta init-form +expression, that expression is evaluated during the processing of the type syntax, +in the global environment. The resulting value then becomes the initial value for +the slot. The semantics of this value is similar to that of a quoted object +appearing as an +.meta init-form +in the +.code defstruct +macro's +.meta slot-specifier +syntax. For example, if the type expression +.codn "(struct s (a int expr))" , +which specifies a slot +.code a +initialized by +.codn expr , +generates a Lisp struct type, the manner in which that type is generated +will resemble that of +.code "(defstruct s nil (a (quote [value-of-expr])))" +where +.code [value-of-expr] +denotes the substitution of the value of +.code expr +which had been obtained by evaluation in the global environment. +Note: if more flexible initialization semantics is required, the application must +define the Lisp struct type first with the desired characteristics, before +processing the FFI struct type. The FFI struct type will then related to the +existing Lisp struct type. + +Those members whose .meta slot name is specified as .code nil is ignored; no instance slots are created in the Lisp type. +If a +.meta init-form +is specified for such a slot, there exists is no situation in which that +form will be evaluated. When a Lisp object is converted to a struct, it must, firstly, be of the struct type specified by |