Sollya User's Manual

Name:

error expression representing an input that is wrongly typed or that cannot be executed

Library names:

sollya_obj_t sollya_lib_error() int sollya_lib_obj_is_error(sollya_obj_t)

Usage:

error : error

Description:

The variable error represents an input during the evaluation of which a type or execution error has been detected or is to be detected. Inputs that are syntactically correct but wrongly typed evaluate to error at some stage. Inputs that are correctly typed but containing commands that depend on side-effects that cannot be performed or inputs that are wrongly typed at meta-level (cf. parse), evaluate to error.

Remark that in contrast to all other elements of the Sollya language, error compares neither equal nor unequal to itself. This provides a means of detecting syntax errors inside the Sollya language itself without introducing issues of two different wrongly typed inputs being equal.

Example 1:

> print(5 + "foo");
error

Example 2:

> error;
error

Example 3:

   > error == error;
   false
   > error != error;
   false

Example 4:

   > correct = 5 + 6;
   > incorrect = 5 + "foo";
   > correct == correct;
   true
   > incorrect == incorrect;
   false
   > errorhappened = !(incorrect == incorrect);
   > errorhappened;
   true