Invoking Units

 

A unit is invoked using the  invoke-unit form:

 
  (invoke-unit f import-variable   ) 

invokes the unit f and returns the value of the last expression within the unit's body. If f is a compound unit, the return value is the invocation value of the last sub-unit specified in the compound unit's with clause.

The number of supplied import-variables must be the same as the number of variables imported by the unit f. Each import-variable must be a global variable; within a unit body, each import-variable must be a built-in global or an imported or exported variable.

When a unit is invoked with invoke-unit, references to built-in global variables in the unit are linked with global variables from the global variable space of the invoke-unit expression.

The  invoke-open-unit procedure is useful for exploring definitions within units:

 
  (invoke-open-unit f name-specifier import-variable   ) 

invokes the unit f like invoke-unit, but some of the unit's internal variables are created as global variables. The way in which internal names are created as global variables depends on the name-specifier clause (which is not an expression):

• If name-specifier is an identifier, then only variables that are exported from f are created as globals. The global variable names are the same as the exported name prefixed with name-specifier and a colon (``:'').
• If name-specifier is a (possibly empty) sequence of identifiers, then name-specifier is used as a path of sub-unit tag names. The unit f will be invoked, but only variables in the sub-unit matching the path are created as globals. For example,

   
    (invoke-open-unit f1@ (A W)) 
  

  invokes f1@, where f1@ must be a compound unit with a sub-unit tagged with A. This sub-unit must also be a compound unit with a sub-unit tagged W. The internal variables of the sub-unit tagged W are created as globals.

  Each globals variable is created using the internal name of the unit variable. The internal variables of a compound unit are all of the internal variables of its subunits; each internal variable name in a compound unit is the internal name in the sub-unit prefixed with the sub-unit's tag and a colon (``:'').

• If name-specifier is not specified, it defaults to the empty path. (In this case, no import-variables can be specified, either.)