created: 20240310165023000
modified: 20240310175033730
tags: [[Call Syntax]]
title: Procedure Definition Syntax
type: text/vnd.tiddlywiki

<<.preamble """What follows is a formal presentation of the syntax of the [[Pragma: \procedure]], using [[railroad diagrams|Railroad Diagrams]]. """>>

! \procedure

There are 2 types of procedure definitions

* Single line definitions
* Multi line definitions

!! Single Line

Single line definitions should only be used for very short bodies, where the procedure name, params and the body fit into 1 line terminated with a line-feed.

<$railroad text="""
"\procedure"
[[<"space">|"Filter Whitespace"]]
"procedure-name"
<"(params)">
[:[[<"space">|"Filter Whitespace"]]]
"body"
"lf"
"""/>

!! Multi Line

The majority of procedure definitions will have a body, that spans over several lines of wikitext. Those procedure definitions are terminated using the "\end" pragma

<$railroad text="""
"\procedure"
[[<"space">|"Filter Whitespace"]]
"procedure-name"
<"(params)">
[:[[<"space">|"Filter Whitespace"]]]
body
"\end"
"""/>

The [[procedure-name|Procedures]] is a sequence of non-whitespace characters other than `(` or `>`.


* <<.place procedure-name>> is a sequence of letters (`A`--`Z`, `a`--`z`), digits (`0`--`9`), hyphens (`-`) and underscores (`_`)
* <<.place body>> is wikitext including [[nested procedures|Pragma: \procedure]]
* <<.place space>> denotes a sequence of [[whitespace characters|Filter Whitespace]]

!! params

The parameter declaration list <<.place (params)>> has the following syntax:

<$railroad text="""
\start none
\end none
"(" [:"sep"] [:{ parameter "sep" }] ")"
"""/>

* <<.place sep>> is any sequence of characters that does not match a <<.place param-name>>. <br>Among other things, this includes commas, spaces and linefeeds.


Each ''individual'' <<.place parameter>> has the following syntax:

<$railroad text="""
\start none
\end none
"param-name" [: [:[[<"space">|"Filter Whitespace"]]] ":" [:[[<"space">|"Filter Whitespace"]]] default ]
"""/>

* <<.place param-name>> is a sequence of letters (`A`--`Z`, `a`--`z`), digits (`0`--`9`), hyphens (`-`) and underscores (`_`).

* <<.place default>> is an optional value of a parameter is specified as follows:

<$railroad text={{$:/editions/tw5.com/railroad/call-parameter-value}}/>

!! body

The <<.place body>> of the definition has the following syntax:

<$railroad text="""
\start none
\end none
{[[<"wikitext">|WikiText]] "lf"}  
"""/>

* <<.place wikitext>> is any sequence of characters that doesn't terminate the macro definition.
** If [[nested procedures|Pragma: \procedure]] are used they need to be at the start of the wikitext. There are the same rules as if the wikitext would be in a tiddler. 
** Pragmas need to be before standard wikitext.

* <<.place lf>> denotes a linefeed.