Show how you would modify the Mini$-$Triangle production rules as

$[20]$

follows:

Allow identifiers to contain single embedded @ characters eg$.$ 'set @ up$\text{'}$ but not 'set @ @up$\text{'},$ nor 'set @$\text{'},$ nor $\text{'}$@up$\text{'})$

Allow real$-$literals eg $\text{'}3\mathrm{.}1416\text{'}($but not $\text{'}3.\text{'}$ nor $\text{'}\mathrm{.}1416\text{'})$

Mini$-$Triangle Production Rules

Program ::$=$ single$-$Command

Command ::$=$ single$-$Command $|$ Command ; single$-$Command

single$-$Command ::$=$ V$-$name :$=$ Expression I Identifier $($ Expression $)$

$|$ if Expression then single$-$Command else single$-$Command $|$ while Expression do single$-$Command let Declaration in single$-$Command begin Command end

Expression : :$=$ primary$-$Expression $|$ Expression Operator primary$-$Expression

primary$-$Expression ::$=$ Integer$-$Literal $|$ V$-$name $|$ Operator primary$-$Expression $|.($ Expression $)$

V$-$name : :$=$ ldentifier

Declaration ::$=$ single$-$Declaration $|$ Declaration ; single$-$Declaration single$-$Declaration : :$=$ const Identifier $-$ Expression $|$ var Identifier : Type$-$denoter

Type$-$denoter ::$=$ Identifier

Operator : :

Identifier : :$=$ Letter $|$ Identifier Letter $|$ 'Identifier Digit Integer$-$Literal ::$=$ Digit $|$ Integer$-$Literal Digit Comment : :$=!$ Graphic$*$ eol