Open Computing ``Hands-On'' Tutorial: January 1994: Figures

Figure 1. Workspace does not match the left-hand side:

bob@here        the workspace


nothing matches


 
Rleft.side      new.stuff       this is a comment 

Figure 2. How ``x'' and ``y'' become ``a''.

x               the workspace



exact match, so: TRUE



Rx      y        first rule rewritten

y                workspace to be this



exact match, so TRUE



Ry      z        second rule

Figure 3. How ``x'' and ``y'' become ``a'', another view:

    x   becomes   y becomes  z becomes  a

    y   becomes   z becomes  a

    z   becomes   a

Figure 4. An operator in the left-hand side.

R$+              $@match

               

lhs              rhs

Figure 5. Tokenizing an address with user and host portions:

gw@wash.dc.gov



tokenized into



"gw" "@" "wash" "." "dc" "." "gov"    in the workspace

Figure 6. A good versus a bad address:

gw@wash.dc.gov      $+ matches

@wash.dc.gov        $+ also matches an incomplete address

Figure 7. How $+@$+ matches the workspace:

workspace   pattern
	
"gw"        "$+"    match one or more

"@"         "@"     exact match
 
"wash"      "$+"    matches one

"."                 or more

"dc"

"."

"gov"

Figure 8. Why $+@$+ doesn't match @wash.dc.gov:

workspace   pattern
	
"@"         "$+"    match one

"wash"              or more
 
"."

"dc"

"."

"gov"

            "@"     match exactly (fails!)

            "$+"

Figure 9. The flow of an address through the rules:

user@host.domain does not match the rule:



R@      $@one



so try the next rule:



R@$+    $@two



which doesn't match so try the next rule, which does:



R$+@$+ $@three