Curl macros introduction (part 3)

[RobertShiplett]

From ndash to n-Soup

The {ndash } macro was very basic. It only has one {return } expression and no logical branches in the code block.

Now for a variant named {ndashi } which only accepts Curl identifiers such as variable names. The only change in the new macro will be its declaration as

Code:

{define-macro public {ndashi ?t1:identifier - ?t2:identifier}

A typical expression using the macro might be

Code:

{let public  str1:String = "this",str2:String = "these"}
{paragraph ndashi'd {ndashi str1 - str2} }

Now for an interesting point: {ndash } would work with the two String variables. But {ndashi } will fail if used in place of {ndash }

Code:

{paragraph ndash'd {ndash str1 - str2} }

  FAILS   {paragraph ndashi'd {ndashi str1 - "that"} }

and it fails with an error stating that an identifier was expected but "that" was received. In the case of {ndash } being passed str1 and str2 the macro expander receives a token in the first case and is content that the value of str2 is characters. But that does not mean that the following could succeed:

Code:

FAILS {paragraph ndash'd {ndash str1 - {value str2} } }
|| as does
FAILS {paragraph ndashi'd {ndashi str1 - {value str2} } }  || Neither can accept an expression

It is essential to test macros and for that there is a Curl mechanism in the form of a macro named {expand-to-string }.

When applied to our unintended use of {ndash }

Code:

{def str1:String = "this"}
{def str2:String = "these"}
{paragraph ndash'd {ndash str1 - str2 } }

{expand-to-string {ndash str1 - str2}}

we see in our test web page

ndash'd this–these

str1 & n-dash & str2

and for

Code:

{paragraph ndashi'd {ndashi str1 - str2 } }
{expand-to-string {ndashi str1 - str2}}

we see in the test page

ndashi'd this–these
str1 & n-dash & str2

Note: Identifier is the name of a Curl class and its instances have a name field.

Next we will build {ndashe } to accept expressions.