Compiler Phases applied to an assignment statement     (Carol Zander, CSS 343)
==================================================

              position := initial + rate * 60;     // assignment operator is :=
                            |
                            v
                     +------------------+
                     | lexical analyzer |
                     +------------------+
                            |
                            v
                id := id + id * 60 ;   
idToken assignToken idToken plusToken idToken multToken numToken semicolonToken
The idTokens and numToken keep track of their associated value, so for clarity
view as:        id1 := id2 + id3 * 60 ;
                            |
                            v
                +------------------------+  
   . . . . . . .| syntactical/semantical |. . . . . . . . . . . . . . . . . .   
  .             |   analyzer (parser)    |                                    .
  .             +------------------------+                                    .
  .                         |                                                 .
  .                         v                                                 .
  .               temp1 := IntToFloat(60)                                     .
  .               temp2 := id3 * temp1                                        .
  .               temp3 := id2 + temp2                                        .
  .               id1   := temp3                                              .
  .uses                     |                                        uses     .
  .grammar                  v                                        grammar  .
  .to check         +----------------+                               to check .
  .for correct      |  optimization  |                               semantics.
  .syntax           +----------------+                                        .
  .                         |                                                 .
  .                         v                                                 .
  .               temp1 := id3 * 60.0                                         .
  .               id1   := id2 + temp1                                        .
  .                         |                                                 .
  .                         v                                                 .
  .                 +----------------+                                        .
  .                 | code generator |                                        .
  .                 +----------------+                                        .
  .                         |                                                 .
  .                         v                                                 .
  .   LOADF  id3,R2   // load float value of id3 in register 2                .
  .   MULF   #60.0,R2 // multiply 60 times contents of register 2             .
  .   LOADF  id2,R1   // load float value of id2 in register 1                .
  .   ADDF   R2,R1    // add contents of register 2 to contents of register 1 .
  .   STOREF R1,id1   // store contents of register 1 at id1                  .
   .                                                                         . 
     .                                                                     .
      . . syntax: form                            semantic: meaning  . . .
          ============                            =================
           assignmentStmt                               :=
           /  |    |  \                               /    \
         id  :=    E   ;                           id1      +
        /     |  / | \                                    /   \
    position    E  +  T                                 id2    *
               /    / | \                                    /   \
              T    T  *  F                                 id3  IntToFloat(60)
             /    /      |
            F    F     number               -- type-checking occurs
           /    /        |                  -- make sure vars are declared
         id   id        60                  -- get addresses from symbol table
        /    /
    initial rate