# Introduction

This is a short guide to what hssqlsystem can do.

## Expression types

<%Command HsSqlSystem typecheckexpression '"2+2"'%>

<%Command HsSqlSystem typecheckexpression '"2+'3'"'%>

<%Command HsSqlSystem typecheckexpression '"2||'3'"'%>

<%Command HsSqlSystem typecheckexpression '"2+a"'%>

<%Command HsSqlSystem typecheckexpression '"noexist(2)"'%>

<%Command HsSqlSystem typecheckexpression '"'dsf'||'sadfsdf'"'%>

<%Command File SelectExpression.sql
(select attname as attribute_name,
       typname as type_name,
       relname as relvar_name
  from pg_attribute inner join pg_class on (attrelid = pg_class.oid)
  inner join pg_type on (atttypid = pg_type.oid)
  inner join (select relname as relvar_name from pg_class where relnamespace =
    (select oid from pg_namespace where nspname = 'public')
    and relkind = 'r') base_relvars on (relname = base_relvars.relvar_name)
  where attnum >= 1)
%>

 ;

<%Command HsSqlSystem typecheckexpression SelectExpression.sql%>

this shouldn't be hint: this needs different command as wrapper
to say it's wrapped in wrapET

<%Command File Select1.sql
select attname as attribute_name,
       typname as type_name,
       relname as relvar_name
  from pg_attribute inner join pg_class on (attrelid = pg_class.oid)
  inner join pg_type on (atttypid = pg_type.oid)
  inner join (select relname as relvar_name from pg_class where relnamespace =
    (select oid from pg_namespace where nspname = 'public')
    and relkind = 'r') base_relvars on (relname = base_relvars.relvar_name)
  where attnum >= 1;
%>

<%Command HsSqlSystem annotatesource -f=Select1.sql%>


: annotate source
aast
ppp

dig some big examples out of chaos

then with errors

## catalog info

<%Command File suppliers_and_parts_ddl.sql
create table s (
       s_no int primary key,
       sname text not null,
       status int not null,
       city text not null
);

create table p (
       p_po int primary key,
       pname text not null,
       color text not null,
       weight int not null,
       city text not null
);

create table sp (
       s_no int not null references s,
       p_no int not null references p,
       qty int not null,
       primary key (s_no,p_no)
);%>

<%Command HsSqlSystem ppcatalog -d=template1 suppliers_and_parts_ddl.sql%>

show catalog

compare catalogs

# extensions

demonstrate create_var extension

+ haskell source?

# stuff to write which will look good here:

function match resolution annotation

better pretty printer for type errors

better pretty printer for annotations

better pretty printer for catalog updates

typechecking ? strings


reference for commands in hssqlppp with examples for each


add sql files for suppliers and parts database?

----

more referency section with each command, a description, plus example
usage of each, and examples of all the options, and how to use a
config file



# ??literatize this file some more:

embed these notes into HsSqlSystem.lhs then provide two documentation
processes, one to htmlize without the source as a command line users
guide, and to htmlize the entire file as a programmers guide: extend
this to commands.lhs as the start of a tutorial/ guide for someone
using this as a library.

-> then the system will allow conversion of HsSqlSystem.lhs to html
   for:
end user guide: how to use the program
library user guide: includes source as example code for haskell programmers
haddock generated documentation
and also to produce an executable.

-> need some way to mark which bits are excluded from the end user guide
   need to be able to pandoc-up the file with syntax highlighting also
   need to have some system to preprocess the file to run embedded
   commands and feed the output into the file before it is
   pandoc'd/syntax highlighted.


~~~~~~~~{.sql}
(select attname as attribute_name,
       typname as type_name,
       relname as relvar_name
  from pg_attribute inner join pg_class on (attrelid = pg_class.oid)
  inner join pg_type on (atttypid = pg_type.oid)
  inner join base_relvars on (relname = base_relvars.relvar_name)
  where attnum >= 1)
~~~~~~~~