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

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

bob@here         [left arrow] the workspace
 [up arrow]

nothing matches

 [down arrow]

Rleft.side      new.stuff       this is a comment

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

x                [left arrow] the workspace

 [up arrow]

exact match, so: TRUE

 [down arrow]

Rx      y        [left arrow]  first rule rewritten

y                [left arrow]  workspace to be this

 [up arrow]

exact match, so TRUE

 [down arrow]

Ry      z        [left arrow]  second rule

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

    x   becomes   [right arrow]  y becomes  [right arrow]  z becomes  [right arrow]  a

    y   becomes   [right arrow]  z becomes  [right arrow]  a

    z   becomes   [right arrow]  a

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

R$+              $@match

 [up arrow]                 [up arrow]

lhs              rhs

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

gw@wash.dc.gov

 [down arrow]

tokenized into

 [down arrow]

"gw" "@" "wash" "." "dc" "." "gov"     [left arrow] in the workspace

Figure 6. A good versus a bad address:

gw@wash.dc.gov      [left arrow]  $+ matches

@wash.dc.gov        [left arrow]  $+ also matches an incomplete address

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

workspace   pattern

"gw"        "$+"    [left arrow]  match one or more

"@"         "@"     [left arrow]  exact match

"wash"      "$+"    [left arrow]  matches one

"."                 [down arrow]  or more

"dc"

"."

"gov"

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

workspace   pattern

"@"         "$+"    [left arrow]  match one

"wash"              [down arrow]  or more

"."

"dc"

"."

"gov"

            "@"     [left arrow]  match exactly (fails!)

            "$+"

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

user@host.domain does not match the rule:

 [down arrow]

R@      $@one

 [down arrow]

so try the next rule:

 [down arrow]

R@$+    $@two

 [down arrow]

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

 [down arrow]

R$+@$+ $@three

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Last Modified: Thursday, 30-Nov-95 16:53:19 PST