Extending Tiny

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Extending Tiny
Programming Language Principles Lecture 19

• Prepared by
• Manuel E. Bermúdez, Ph.D.
• Associate Professor
• University of Florida

2
Extending Tiny

• Let's add a few more constructs to Tiny.
• The repeat statement (a la Pascal).
• Code
• n E1
• E2
• iffalse n

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The Repeat Statement (a la Pascal)

• E ?
• code ?(?) gen(code ?(2), "iffalse",next ?(?))
• next ?(?) next ?(2) 1
• top ?(?) top ?(2) - 1
• error ?(?) if type ?(2)"bool"
• then error ?(2)
• else gen(error ?(2), "non-bool
  exp")
• type ?(?) "statement"

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Extending Tiny (contd)

• The one-armed "if".
• Code
• E1
• iffalse n
• E2
• n

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The One-Armed "if"

• E ?
• code ?(2) gen(code ?(1), "iffalse",next ?(2))
• next ?(2) next ?(1) 1
• top ?(2) top ?(1) - 1
• error ?(2) if type ?(1)"bool"
• then error ?(1)
• else gen(error ?(1), "non-bool exp")
• type ?(?) "statement

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Extending Tiny (contd)

• Conditional Expression
• Code
• E1
• iffalse n
• E2
• goto m
• n E3
• m

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Conditional Expression

• E ?
• code ?(2) gen(code ?(1), "iffalse",next
  ?(2)1)
• next ?(2) next ?(1) 1
• top ?(2) top ?(1) - 1
• error ?(2) if type ?(1)"bool"
• then error ?(1)
• else gen(error ?(1), "non-bool exp")

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Conditional Expression (contd)

• code ?(3) gen(code ?(2), goto",next ?(3))
• next ?(3) next ?(2) 1
• error ?(?) if type ?(2) type ?(3)
• then error ?(3)
• else gen(error ?(3), type
  mismatch")
• top ?(?) top ?(3) - 1
• type ?(?) type ?(2) ??? type ?(3) ???

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Extending Tiny

• Prefix auto-increment.
• Problematic. If x has not been defined, what
  location do we reserve for it on the stack ?
• Code
• load n
• lit 1
• add
• save n
• load n n lookup(x)

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Prefix Auto-Increment

• E ?
• code ?(?)
• if lookup(x)0 then code ?(?)
• else gen(
• gen(
• gen(
• gen(
• gen(code ?(?), "load", lookup(x)),
• "lit", 1),
• "add"),
• "save", lookup(x)),
• "load", lookup(x))

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Prefix Auto-Increment (contd)

• error ?(?) if lookup(x) !0
• then error ?(?)
• else gen(error ?(?), "var
  undefined")
• next ?(?) next ?(?) 5
• top ?(?) top ?(?) 1 ???
• type ?(?) ???

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A Sample "Compilation" Using Tiny's AG

• To save time (and space), we'll track only code,
  next, top

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A Sample "Compilation" Using Tiny's AG (contd)

• Tiny program
• program teeny
• assign x read
• if x1
• then assign x0
• else output x end
• teeny.

• Code file
• read
• load 1
• lit 1
• equal
• iffalse 9
• lit 0
• save 1
• goto 11
• load 1
• print
• stop.

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Extending Tiny
Programming Language Principles Lecture 19

• Prepared by
• Manuel E. Bermúdez, Ph.D.
• Associate Professor
• University of Florida