476 lines
16 KiB
Plaintext
476 lines
16 KiB
Plaintext
#!/usr/bin/env nomsu -V4.11.12.8
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#
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This file contains compile-time actions that define basic control flow structures
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like "if" statements and loops.
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use "core/metaprogramming.nom"
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use "core/operators.nom"
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use "core/errors.nom"
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# No-Op
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test:
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do nothing
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(do nothing) compiles to ""
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# Conditionals
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test:
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if (no):
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barf "conditional fail"
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(if %condition %if_body) compiles to "\
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..if \(%condition as lua expr) then
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\(%if_body as lua)
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end"
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test:
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unless (yes):
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barf "conditional fail"
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(unless %condition %unless_body) parses as (if (not %condition) %unless_body)
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[if %condition %if_body else %else_body, unless %condition %else_body else %if_body] \
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..all compile to "\
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..if \(%condition as lua expr) then
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\(%if_body as lua)
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else
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\(%else_body as lua)
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end"
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# Conditional expression (ternary operator)
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# Note: this uses a function instead of "(condition and if_expr or else_expr)"
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because that breaks if %if_expr is falsey, e.g. "x < 5 and false or 99"
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test:
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assume ((1 if (yes) else 2) == 1)
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assume ((1 if (no) else 2) == 2)
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[..]
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%when_true_expr if %condition else %when_false_expr
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%when_true_expr if %condition otherwise %when_false_expr
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%when_false_expr unless %condition else %when_true_expr
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%when_false_expr unless %condition then %when_true_expr
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..all compile to:
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# If %when_true_expr is guaranteed to be truthy, we can use Lua's idiomatic
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equivalent of a conditional expression: (cond and if_true or if_false)
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if {Text, List, Dict, Number}.(%when_true_expr.type):
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return (Lua "(\(%condition as lua expr) and \(%when_true_expr as lua expr) or \(%when_false_expr as lua expr))")
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..else:
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# Otherwise, need to do an anonymous inline function (yuck, too bad lua
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doesn't have a proper ternary operator!)
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To see why this is necessary consider: (random()<.5 and false or 99)
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return (..)
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Lua "\
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..((function()
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if \(%condition as lua expr) then
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return \(%when_true_expr as lua expr)
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else
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return \(%when_false_expr as lua expr)
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end
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end)())"
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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# GOTOs
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test:
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%i = 0
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--- %loop ---
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%i += 1
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unless (%i == 10):
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go to %loop
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assume (%i == 10)
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--- (Loop) ---
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%i -= 1
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unless (%i == 0):
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go to (Loop)
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assume (%i == 0)
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(--- %label ---) compiles to "\
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..::label_\((%label.stub::as lua id) if (%label.type == "Action") else (%label as lua identifier))::"
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(go to %label) compiles to "\
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..goto label_\((%label.stub::as lua id) if (%label.type == "Action") else (%label as lua identifier))"
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# Basic loop control
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(stop %var) compiles to:
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if %var:
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return (Lua "goto stop_\(%var as lua identifier)")
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..else:
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return (Lua "break")
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(do next %var) compiles to:
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if %var:
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return (Lua "goto continue_\(%var as lua identifier)")
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..else:
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return (Lua "goto continue")
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(---stop %var ---) compiles to "\
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..::stop_\(%var as lua identifier)::"
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(---next %var ---) compiles to "\
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..::continue_\(%var as lua identifier)::"
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# While loops
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test:
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%x = 0
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repeat while (%x < 10): %x += 1
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assume (%x == 10)
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repeat while (%x < 20): stop
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assume (%x == 10)
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repeat while (%x < 20):
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%x += 1
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if (yes):
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do next
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barf "Failed to 'do next'"
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assume (%x == 20)
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(repeat while %condition %body) compiles to:
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%lua = (Lua "while \(%condition as lua expr) do\n \(%body as lua)")
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if (%body has subtree \(do next)):
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%lua::append "\n ::continue::"
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%lua::append "\nend --while-loop"
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return %lua
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(repeat %body) parses as (repeat while (yes) %body)
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(repeat until %condition %body) parses as (repeat while (not %condition) %body)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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test:
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%nums = []
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for %x in 1 to 5:
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%nums::add %x
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assume (%nums == [1, 2, 3, 4, 5])
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%nums = []
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for %x in 1 to 5 via 2:
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%nums::add %x
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assume (%nums == [1, 3, 5])
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%nums = []
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for %outer in 1 to 100:
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for %inner in %outer to (%outer + 2):
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if (%inner == 2):
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%nums::add -2
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do next %inner
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%nums::add %inner
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if (%inner == 5):
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stop %outer
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assume (%nums == [1, -2, 3, -2, 3, 4, 3, 4, 5])
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# Numeric range for loops
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[..]
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for %var in %start to %stop by %step %body
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for %var in %start to %stop via %step %body
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..all compile to:
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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%lua = (Lua "for \(%var as lua identifier)=\(%start as lua expr),\(%stop as lua expr),\(%step as lua expr) do")
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%lua::append "\n " (%body as lua)
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if (%body has subtree \(do next)):
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%lua::append "\n ::continue::"
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if (%body has subtree \(do next %var)):
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%lua::append "\n " (\(---next %var ---) as lua)
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%lua::append "\nend --numeric for-loop"
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if (%body has subtree \(stop %var)):
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%inner_lua = %lua
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%lua = (Lua "do -- scope for stopping for-loop\n ")
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%lua::append %inner_lua "\n "
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%lua::append (\(---stop %var ---) as lua)
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%lua::append "\nend -- end of scope for stopping for-loop"
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return %lua
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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(for %var in %start to %stop %body) parses as (..)
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for %var in %start to %stop via 1 %body
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test:
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%x = 0
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repeat 5 times: %x += 1
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assume %x == 5
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(repeat %n times %body) parses as (for (=lua "_XXX_") in 1 to %n %body)
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test:
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%a = [10, 20, 30, 40, 50]
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%b = []
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for %x in %a:
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%b::add %x
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assume (%a == %b)
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%b = []
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for %x in %a:
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if (%x == 10):
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do next %x
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if (%x == 50):
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stop %x
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%b::add %x
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assume (%b == [20, 30, 40])
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# For-each loop (lua's "ipairs()")
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(for %var in %iterable at %i %body) compiles to:
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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%lua = (..)
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Lua "\
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..for \(%i as lua identifier),\(%var as lua identifier) in ipairs(\(%iterable as lua expr)) do
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"
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%lua::append (%body as lua)
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if (%body has subtree \(do next)):
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%lua::append "\n ::continue::"
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if (%body has subtree \(do next %var)):
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%lua::append "\n " (\(---next %var ---) as lua)
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%lua::append "\nend --for \(%var as lua identifier) loop"
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if (%body has subtree \(stop %var)):
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%inner_lua = %lua
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%lua = (Lua "do -- scope for stopping for-loop\n ")
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%lua::append %inner_lua "\n "
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%lua::append (\(---stop %var ---) as lua)
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%lua::append "\nend -- end of scope for stopping for-loop"
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return %lua
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(for %var in %iterable %body) parses as (for %var in %iterable at (=lua "__") %body)
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test:
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%d = {a: 10, b: 20, c: 30, d: 40, e: 50}
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%result = []
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for %k = %v in %d:
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if (%k == "a"):
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do next %k
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if (%v == 20):
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do next %v
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%result::add "\%k = \%v"
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assume ((%result sorted) == ["c = 30", "d = 40", "e = 50"])
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# Dict iteration (lua's "pairs()")
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[for %key = %value in %iterable %body, for %key %value in %iterable %body] \
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..all compile to:
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%lua = (Lua "for \(%key as lua identifier),\(%value as lua identifier) in pairs(\(%iterable as lua expr)) do")
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%lua::append "\n " (%body as lua)
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if (%body has subtree \(do next)):
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%lua::append "\n ::continue::"
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if (%body has subtree \(do next %key)):
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%lua::append "\n " (\(---next %key ---) as lua)
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if (%body has subtree \(do next %value)):
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%lua::append "\n " (\(---next %value ---) as lua)
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%lua::append "\nend --foreach-loop"
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%stop_labels = (Lua "")
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if (%body has subtree \(stop %key)):
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%stop_labels::append "\n" (\(---stop %key ---) as lua)
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if (%body has subtree \(stop %value)):
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%stop_labels::append "\n" (\(---stop %value ---) as lua)
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if ((size of "\%stop_labels") > 0):
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%inner_lua = %lua
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%lua = (Lua "do -- scope for stopping for % = % loop\n ")
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%lua::append %inner_lua %stop_labels "\nend"
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return %lua
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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test:
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when:
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(1 == 2) (100 < 0):
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barf "bad conditional"
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(1 == 0) (1 == 1) %not_a_variable.x: do nothing
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(1 == 1):
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barf "bad conditional"
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(1 == 2):
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barf "bad conditional"
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else:
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barf "bad conditional"
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# Multi-branch conditional (if..elseif..else)
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(when %body) compiles to:
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%code = (Lua "")
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%clause = "if"
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%else_allowed = (yes)
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unless (%body.type is "Block"):
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compile error at %body "'if' expected a Block, but got a \(%body.type)." "\
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..Perhaps you forgot to put a ':' after 'if'?"
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for %line in %body:
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unless (..)
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((%line.type is "Action") and ((size of %line) >= 2)) and (..)
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%line.(size of %line) is "Block" syntax tree
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..:
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compile error at %line "Invalid line for the body of an 'if' block." "\
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..Each line should contain one or more conditional expressions followed by a block, or "else" followed \
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..by a block."
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%action = %line.(size of %line)
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if ((%line.1 is "else") and ((size of %line) == 2)):
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unless %else_allowed:
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compile error at %line "You can't have two 'else' blocks." "\
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..Merge all of the 'else' blocks together."
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unless ((size of "\%code") > 0):
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compile error at %line "\
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..You can't have an 'else' block without a preceding condition"
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.."\
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..If you want the code in this block to always execute, you don't need a conditional block around it. \
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..Otherwise, make sure the 'else' block comes last."
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%code::append "\nelse\n " (%action as lua)
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%else_allowed = (no)
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..else:
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%code::append %clause " "
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for %i in 1 to ((size of %line) - 1):
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if (%i > 1):
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%code::append " or "
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%code::append (%line.%i as lua expr)
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%code::append " then\n " (%action as lua)
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%clause = "\nelseif"
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if ((size of "\%code") == 0):
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compile error at %body "'if' block has an empty body." "\
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..This means nothing would happen, so the 'if' block should be deleted."
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%code::append "\nend --when"
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return %code
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test:
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if 5 is:
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1 2 3:
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barf "bad switch statement"
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4 5:
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do nothing
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5 6:
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barf "bad switch statement"
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else:
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barf "bad switch statement"
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# Switch statement
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[if %branch_value is %body, when %branch_value is %body] all compile to:
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%code = (Lua "")
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%clause = "if"
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%else_allowed = (yes)
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define mangler
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unless (%body.type is "Block"):
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compile error at %body "'if' expected a Block, but got a \(%body.type)" "\
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..Perhaps you forgot to put a ':' after the 'is'?"
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for %line in %body:
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unless (..)
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((%line.type is "Action") and ((size of %line) >= 2)) and (..)
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%line.(size of %line) is "Block" syntax tree
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..:
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compile error at %line "Invalid line for 'if' block." "\
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..Each line should contain expressions followed by a block, or "else" followed by a block"
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%action = %line.(size of %line)
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if ((%line.1 is "else") and ((size of %line) == 2)):
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unless %else_allowed:
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compile error at %line "You can't have two 'else' blocks." "\
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..Merge all of the 'else' blocks together."
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unless ((size of "\%code") > 0):
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compile error at %line "\
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..You can't have an 'else' block without a preceding condition"
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.."\
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..If you want the code in this block to always execute, you don't need a conditional block around it. \
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..Otherwise, make sure the 'else' block comes last."
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%code::append "\nelse\n " (%action as lua)
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%else_allowed = (no)
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..else:
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%code::append %clause " "
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for %i in 1 to ((size of %line) - 1):
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if (%i > 1):
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%code::append " or "
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%code::append "\(mangle "branch value") == " (%line.%i as lua expr)
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%code::append " then\n " (%action as lua)
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%clause = "\nelseif"
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if ((size of "\%code") == 0):
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compile error at %body "'if' block has an empty body." "\
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..This means nothing would happen, so the 'if' block should be deleted."
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%code::append "\nend --when"
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return (..)
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Lua "\
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..do --if % is...
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local \(mangle "branch value") = \(%branch_value as lua expr)
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\%code
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end -- if % is..."
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# Do/finally
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(do %action) compiles to "do\n \(%action as lua)\nend -- do"
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test:
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%d = {}
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try:
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do:
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%d.x = "bad"
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barf
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..then always:
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%d.x = "good"
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assume (%d.x == "good")
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(do %action then always %final_action) compiles to:
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define mangler
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return (..)
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Lua "\
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..do
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local \(mangle "fell_through") = false
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local \(mangle "ok"), \(mangle "ret") = pcall(function()
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\(%action as lua)
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\(mangle "fell_through") = true
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end)
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\(%final_action as lua)
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if not \(mangle "ok") then error(ret, 0) end
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if not \(mangle "fell_through") then return ret end
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end"
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test:
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assume ((result of: return 99) == 99)
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# Inline thunk:
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(result of %body) compiles to "\(\(-> %body) as lua)()"
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test:
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%t = [1, [2, [[3], 4], 5, [[[6]]]]]
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%flat = []
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for % in recursive %t:
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if ((lua type of %) is "table"):
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for %2 in %:
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recurse % on %2
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..else:
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%flat::add %
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assume (sorted %flat) == [1, 2, 3, 4, 5, 6]
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# Recurion control flow
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(for %var in recursive %structure %body) compiles to:
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with local compile actions:
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define mangler
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(recurse %v on %x) compiles to (..)
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Lua "table.insert(\(mangle "stack \(%v.1)"), \(%x as lua expr))"
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%lua = (..)
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Lua "\
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..do
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local \(mangle "stack \(%var.1)") = List{\(%structure as lua expr)}
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while #\(mangle "stack \(%var.1)") > 0 do
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\(%var as lua expr) = table.remove(\(mangle "stack \(%var.1)"), 1)
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\(%body as lua)"
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if (%body has subtree \(do next)):
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%lua::append "\n ::continue::"
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if (%body has subtree \(do next %var)):
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%lua::append "\n \(\(---next %var ---) as lua)"
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%lua::append "\n end -- Recursive loop"
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if (%body has subtree \(stop %var)):
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%lua::append "\n \(\(---stop %var ---) as lua)"
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%lua::append "\nend -- Recursive scope"
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return %lua
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