Code as data (RubyConfBY 2019 edition)

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CODE AS DATA DENIS DEFREYNE (PRONOUNS: HE/HIM) @DDFREYNE / DENIS.WS RUBYCONFBY 2019 2019-04-06

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nanoc / cri / ddmemoize / ddmetrics / …

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I work at

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$$$

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Why do we need a pricing algorithm?       

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Why do we need a pricing algorithm?    * fixed price?   

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Why do we need a pricing algorithm?    * fixed price? unfair.   

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Why do we need a pricing algorithm?    * fixed price? unfair.  * price per hour? 

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Why do we need a pricing algorithm?    * fixed price? unfair.  * price per hour? hard to calculate. 

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Why do we need a pricing algorithm?    * fixed price? unfair.  * price per hour? hard to calculate.  * wait and see what the price turns out to be?

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Why do we need a pricing algorithm?    * fixed price? unfair.  * price per hour? hard to calculate.  * wait and see what the price turns out to be? risky.

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Why do we need a pricing algorithm?    * fixed price? unfair.  * price per hour? hard to calculate. * wait and see what the price turns out to be? risky.  * algorithm?

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Why do we need a pricing algorithm?    * fixed price? unfair.  * price per hour? hard to calculate. * wait and see what the price turns out to be? risky.  * algorithm? yes!

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$$$

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$$$ * Business need to know  why prices are the way they are           

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$$$ * Business need to know  why prices are the way they are  * Developers need to be involved  to implement new formulas     

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$$$ * Business need to know  why prices are the way they are  * Developers need to be involved  to implement new formulas  * Developers have no good way  to verify new formulas     

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$$$ * Business need to know  why prices are the way they are  * Developers need to be involved  to implement new formulas  * Developers have no good way  to verify new formulas  * It is difficult  to dry-run new formulas

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def total_price 200 + volume * distance end

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THE IDEA

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def total_price 200 + volume * distance end

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def total_price 200 + volume * distance end sum

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def total_price 200 + volume * distance end sum product

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def total_price 200 + volume * distance end sum product variable

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def total_price 200 + volume * distance end sum product constant variable

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No content

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class SumExpr def initialize(left, right) @left = left @right = right end end

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class SumExpr def initialize(left, right) @left = left @right = right end end class ProductExpr def initialize(left, right) @left = left @right = right end end

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class SumExpr def initialize(left, right) @left = left @right = right end end class ProductExpr def initialize(left, right) @left = left @right = right end end class ConstantExpr def initialize(value) @value = value end end 

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def price_formula SumExpr.new( ConstantExpr.new(200), ProductExpr.new( VariableExpr.new(Tvolume), VariableExpr.new(Tdistance), ) ) end

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params = { volume: 20, distance: 200, } price_formula.evaluate(params)

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    params = { volume: 20, distance: 200, } price_formula.evaluate(params)    4200

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def evaluate(params)

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class VariableExpr def initialize(name) @name = name end def evaluate(params) params.fetch(@name) end end

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class ConstantExpr def initialize(value) @value = value end def evaluate(_params) @value end end

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class SumExpr def initialize(left, right) @left = left @right = right end def evaluate(params) @left.evaluate(params) + @right.evaluate(params) end end 

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class ProductExpr def initialize(left, right) @left = left @right = right end def evaluate(params) @left.evaluate(params) * @right.evaluate(params) end end 

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    params = { volume: 20, distance: 200, }    

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    params = { volume: 20, distance: 200, } price_formula.evaluate(params)   

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    params = { volume: 20, distance: 200, } price_formula.evaluate(params)    4200

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THE POINT

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SumExpr.new( ConstantExpr.new(200), ProductExpr.new( VariableExpr.new(Tvolume), VariableExpr.new(Tdistance), ) )           

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SumExpr.new( ConstantExpr.new(200), ProductExpr.new( VariableExpr.new(Tvolume), VariableExpr.new(Tdistance), ) )    + Z[> 4200 const Z[> 200 * Z[> 4000 var volume Z[> 20 var distance Z[> 200

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class Node def initialize(name, value, children) @name = name @value = value @children = children end end

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+ Z[> 4200 const Z[> 200 * Z[> 4000 var volume Z[> 20 var distance Z[> 200

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+ Z[> 4200 const Z[> 200 * Z[> 4000 var volume Z[> 20 var distance Z[> 200 Node.new("+", 4200, [const_node, product_node])

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+ Z[> 4200 const Z[> 200 * Z[> 4000 var volume Z[> 20 var distance Z[> 200 Node.new("+", 4200, [const_node, product_node]) Node.new("var volume", 20, [])

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class VariableExpr def initialize(name) @name = name end def evaluate(params) params.fetch(@name) end end

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class VariableExpr def initialize(name) @name = name end def evaluate(params) Node.new( "var #{@name}", params.fetch(@name), [], ) end end

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class ConstantExpr def initialize(value) @value = value end def evaluate(_params) @value end end

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class ConstantExpr def initialize(value) @value = value end def evaluate(_params) Node.new( 'const', @value, [], ) end end

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class SumExpr def initialize(left, right) @left = left @right = right end def evaluate(params) left_node = @left.evaluate(params) right_node = @right.evaluate(params) Node.new( '+', left_node.value + right_node.value, [left_node, right_node], ) end end

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class ProductExpr def initialize(left, right) @left = left @right = right end def evaluate(params) left_node = @left.evaluate(params) right_node = @right.evaluate(params) Node.new( '*', left_node.value * right_node.value, [left_node, right_node], ) end end

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class Node def to_s # … left to your imagination … end end

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puts price_formula.evaluate(params)           

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puts price_formula.evaluate(params) + >?> 4200 const >?> 200 * >?> 4000 var volume >?> 20 var distance >?> 200

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puts price_formula.evaluate(params).value           

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puts price_formula.evaluate(params).value    4200       

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THE BEST PART: The price formula did not change!

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* Business need to know  why prices are the way they are  * Developers need to be involved  to implement new formulas  * Developers have no good way  to verify new formulas  * It is difficult  to dry-run new formulas

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THE POINT (PART II): THE GUI

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"200 + volume * distance"            

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"200 + volume * distance" C> SumExpr.new( ConstantExpr.new(200), ProductExpr.new( VariableExpr.new(Nvolume), VariableExpr.new(Ndistance), ) )

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parse("200 + volume * distance") C> SumExpr.new( ConstantExpr.new(200), ProductExpr.new( VariableExpr.new(Nvolume), VariableExpr.new(Ndistance), ) )

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require 'd-parse'

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module Grammar extend DParseijDSL # … end

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DIGIT = char_in('0'..'9')

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CONSTANT_EXPR = repeat1(DIGIT) .capture .map { |d| ConstantExpr.new(d.to_i(10)) }

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VARIABLE_EXPR = repeat1(char_in('a'..'z')) .capture .map { |d| VariableExpr.new(d) }

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OPERAND = alt( CONSTANT_EXPR, VARIABLE_EXPR, )

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OPERATOR = alt( char('+'), char('*'), ).capture

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OP_SEQ = intersperse( OPERAND, OPERATOR, ).map { |d| OpSeqExpr.new(d) }

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ROOT = seq( OP_SEQ, eof, ).first

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input = "200 + volume * distance"

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input = "200 + volume * distance" raw_expr = GrammarijROOT.apply( input_string, )

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OpSeqExpr.new( [ ConstantExpr.new(200), "+", VariableExpr.new(Tvolume), "*", VariableExpr.new(Tdistance), ] )

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def resolve_op_seq_exprs(expr) # … apply shunting yard or so … end

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resolve_op_seq_exprs(raw_expr)

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SumExpr.new( ConstantExpr.new(200), ProductExpr.new( VariableExpr.new(Tvolume), VariableExpr.new(Tdistance), ) )

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input = "200 + volume * distance"

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input = "200 + volume * distance" GrammarijROOT.apply( input, )

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input = "200 + volume * distance" resolve_op_seq_exprs( GrammarijROOT.apply( input, ), )

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input = "200 + volume * distance" price_formula = resolve_op_seq_exprs( GrammarijROOT.apply( input, ), )

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params = { volume: 20, distance: 200, }    

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params = { volume: 20, distance: 200, } puts price_formula.evaluate(params).value   

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params = { volume: 20, distance: 200, } puts price_formula.evaluate(params).value    4200

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THE POINT (PART III): MORE BENEFITS

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MORE BENEFITS:    

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MORE BENEFITS: * Versioning & locking   

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MORE BENEFITS: * Versioning & locking  * Translate to Ruby  

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MORE BENEFITS: * Versioning & locking  * Translate to Ruby * Translate to SQL 

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MORE BENEFITS: * Versioning & locking  * Translate to Ruby * Translate to SQL  * Compile with LLVM

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Is this over-engineering?

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TAKE-AWAYS

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* It’s much easier to reason about data  than to reason about code.    

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* It’s much easier to reason about data  than to reason about code. * Try novel approaches; they can  reveal new opportunities.

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DENIS DEFREYNE @DDFREYNE / DENIS.WS