Submitted by: @sim1984

Use CONNECT or CREATE DATABASE to specify a database
SQL> connect 'localhost/3051:horses' user 'sysdba' password 'masterkey';
Database: 'localhost/3051:horses', User: sysdba
SQL> set term ^;
SQL> execute block
CON> returns (c integer)
CON> as
CON> DECLARE VARIABLE b boolean;
CON> DECLARE function f1() returns boolean as
CON> begin
CON> return true;
CON> end
CON> begin
CON> c = 0;
CON> b = f1();
CON> --IF (f1()) THEN c = 1;
CON> IF (b) THEN c = 1;
CON> suspend;
CON> end^

       C

============
1

SQL> execute block
CON> returns (c integer)
CON> as
CON> DECLARE VARIABLE b boolean;
CON> DECLARE function f1() returns boolean as
CON> begin
CON> return true;
CON> end
CON> begin
CON> c = 0;
CON> b = f1();
CON> IF (f1()) THEN c = 1;
CON> --IF (b) THEN c = 1;
CON> suspend;
CON> end^
Statement failed, SQLSTATE = 22000
Dynamic SQL Error
-SQL error code = -104
-Invalid usage of boolean expression

Commits: 8738972 FirebirdSQL/fbt-repository@2a7039a