413 lines
16 KiB
Plaintext
413 lines
16 KiB
Plaintext
#..
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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/text.nom"
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use "core/operators.nom"
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# No-Op
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immediately
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compile [do nothing] to: Lua ""
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# Conditionals
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immediately
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compile [if %condition %if_body] to
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Lua ".."
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if \(%condition as lua expr) then
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\(%if_body as lua statements)
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end
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parse [unless %condition %unless_body] as: if (not %condition) %unless_body
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compile [if %condition %if_body else %else_body, unless %condition %else_body else %if_body] to
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Lua ".."
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if \(%condition as lua expr) then
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\(%if_body as lua statements)
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else
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\(%else_body as lua statements)
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end
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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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immediately
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compile [..]
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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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..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: %when_true_expr.type in {Text:yes, List:yes, Dict:yes, Number:yes}
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return
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Lua value ".."
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(\(%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 value ".."
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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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# GOTOs
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immediately
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compile [=== %label ===, --- %label ---, *** %label ***] to
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Lua "::label_\(%label as lua identifier)::;"
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compile [go to %label] to
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Lua "goto label_\(%label as lua identifier);"
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# Basic loop control
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immediately
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compile [do next] to: Lua "continue;"
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compile [stop] to: Lua "break;"
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# Helper function
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immediately
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compile [if %tree has subtree %subtree where %condition %body] to
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Lua ".."
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for \(%subtree as lua expr) in coroutine.wrap(function() nomsu:walk_tree(\(%tree as lua expr)) end) do
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if Types.is_node(\(%subtree as lua expr)) then
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if \(%condition as lua expr) then
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\(%body as lua statements)
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break;
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end
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end
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end
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# While loops
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immediately
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compile [do next repeat] to: Lua "goto continue_repeat;"
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compile [stop repeating] to: Lua "goto stop_repeat;"
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compile [repeat while %condition %body] to
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%lua <-
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Lua ".."
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while \(%condition as lua expr) do
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\(%body as lua statements)
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if %body has subtree % where
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(%.type = "Action") and ((%'s stub) is "do next repeat")
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..
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to %lua write "\n ::continue_repeat::;"
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to %lua write "\nend --while-loop"
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if %body has subtree % where
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(%.type = "Action") and ((%'s stub) is "stop repeating")
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..
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%lua <-
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Lua ".."
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do -- scope of "stop repeating" label
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\%lua
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::stop_repeat::;
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end -- end of "stop repeating" label scope
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return %lua
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parse [repeat %body] as: repeat while (yes) %body
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parse [repeat until %condition %body] as: repeat while (not %condition) %body
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compile [..]
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repeat %n times %body
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..to
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%lua <-
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Lua ".."
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for i=1,\(%n as lua expr) do
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\(%body as lua statements)
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if %body has subtree % where
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(%.type = "Action") and ((%'s stub) is "do next repeat")
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..: to %lua write "\n ::continue_repeat::;"
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to %lua write "\nend --numeric for-loop"
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if %body has subtree % where
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(%.type = "Action") and ((%'s stub) is "stop repeating")
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..
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%lua <-
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Lua ".."
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do -- scope of "stop repeating" label
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\%lua
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::stop_repeat::;
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end -- end of "stop repeating" label scope
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return %lua
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# For loop control flow
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immediately
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compile [stop %var] to
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Lua "goto stop_\(%var as lua identifier);"
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compile [do next %var] to
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Lua "goto continue_\(%var as lua identifier);"
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# Numeric range for loops
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immediately
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compile [..]
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for %var from %start to %stop by %step %body
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for %var from %start to %stop via %step %body
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..to
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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assume (%var.type is "Var") or barf "Loop expected variable, not: \(%var's source code)"
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%lua <-
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Lua ".."
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for \(%var as lua expr)=\(%start as lua expr),\(%stop as lua expr),\(%step as lua expr) do
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\(%body as lua statements)
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "do next %") and
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%.value.3.value is %var.value
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..: to %lua write "\n ::continue_\(%var as lua identifier)::;"
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to %lua write "\nend --numeric for-loop"
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "stop %") and
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%.value.2.value is %var.value
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..
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%lua <-
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Lua ".."
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do -- scope for stopping for-loop
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\%lua
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::stop_\(%var as lua identifier)::;
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end -- end of scope for stopping for-loop
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return %lua
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immediately
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parse [for %var from %start to %stop %body] as: for %var from %start to %stop via 1 %body
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parse [..]
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for all %start to %stop by %step %body
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for all %start to %stop via %step %body
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..as: for % from %start to %stop via %step %body
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parse [for all %start to %stop %body] as: for all %start to %stop via 1 %body
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# For-each loop (lua's "ipairs()")
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immediately
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compile [for %var in %iterable %body] to
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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assume (%var.type is "Var") or barf "Loop expected variable, not: \(%var's source code)"
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%lua <-
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Lua ".."
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for i,\(%var as lua identifier) in ipairs(\(%iterable as lua expr)) do
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\(%body as lua statements)
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "do next %") and
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%.value.3.value is %var.value
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..: to %lua write (Lua "\n ::continue_\(%var as lua identifier)::;")
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to %lua write "\nend --foreach-loop"
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "stop %") and
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%.value.2.value is %var.value
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..
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%lua <-
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Lua ".."
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do -- scope for stopping for-loop
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\%lua
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::stop_\(%var as lua identifier)::;
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end -- end of scope for stopping for-loop
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return %lua
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parse [for all %iterable %body] as: for % in %iterable %body
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# Dict iteration (lua's "pairs()")
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immediately
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compile [for %key = %value in %iterable %body] to
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# This uses Lua's approach of only allowing loop-scoped variables in a loop
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assume (%key.type is "Var") or barf "Loop expected variable, not: \(%key's source code)"
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assume (%value.type is "Var") or barf "Loop expected variable, not: \(%value's source code)"
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%lua <-
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Lua ".."
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for \(%key as lua identifier),\(%value as lua identifier) in pairs(\(%iterable as lua expr)) do
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\(%body as lua statements)
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "do next %") and
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%.value.3.value is %key.value
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..: to %lua write (Lua "\n ::continue_\(%key as lua identifier)::;")
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "do next %") and
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%.value.3.value is %value.value
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..: to %lua write (Lua "\n ::continue_\(%value as lua identifier)::;")
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to %lua write "\nend --foreach-loop"
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%stop_labels <- (Lua "")
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "stop %") and
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%.value.2.value is %key.value
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..: to %stop_labels write "\n::stop_\(%key as lua identifier)::;"
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if %body has subtree % where
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(%.type = "Action") and
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((%'s stub) is "stop %") and
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%.value.2.value is %value.value
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..: to %stop_labels write "\n::stop_\(%value as lua identifier)::;"
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if: (length of %stop_labels) > 0
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%lua <-
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Lua ".."
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do -- scope for stopping for % = % loop
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\%lua
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\%stop_labels
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end
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return %lua
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# Switch statement/multi-branch if
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immediately
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compile [when %body] to
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%code <- (Lua "")
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%fallthroughs <- []
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%is_first <- (yes)
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%seen_else <- (no)
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for %func_call in %body.value
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assume (%func_call.type is "Action") or barf ".."
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Invalid format for 'when' statement. Only '*' blocks are allowed.
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%tokens <- %func_call.value
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with {..}
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%star: %tokens.1
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%condition: %tokens.2
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%action: %tokens.3
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..
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assume ((%star and (%star.type is "Word")) and (%star.value is "*")) or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*'
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assume %condition or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"
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if: %action is (nil)
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr));"
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do next %func_call
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if: (%condition.type is "Word") and (%condition.value is "else")
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assume (not %is_first) or barf "'else' clause cannot be first in 'when % = ?' block"
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to %code write "\nelse\n "
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to %code write: %action as lua statements
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%seen_else <- (yes)
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..else
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assume (not %seen_else) or barf "'else' clause needs to be last in 'when' block"
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr));"
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to %code write "\("if" if %is_first else "\nelseif") "
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for %i=%condition in %fallthroughs
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if (%i > 1): to %code write " or "
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to %code write %condition
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to %code write " then\n "
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to %code write (%action as lua statements)
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%fallthroughs <- []
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%is_first <- (no)
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assume (%fallthroughs = []) or barf "Unfinished fallthrough conditions in 'when' block"
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assume ((length of %code) > 0) or barf "Empty body for 'when' block"
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to %code write "\nend --when"
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return %code
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# Switch statement
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immediately
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compile [when %branch_value = ? %body, when %branch_value is ? %body] to
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%code <- (Lua "")
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%fallthroughs <- []
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%is_first <- (yes)
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%seen_else <- (no)
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for %func_call in %body.value
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assume (%func_call.type is "Action") or barf ".."
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Invalid format for 'when' statement. Only '*' blocks are allowed.
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%tokens <- %func_call.value
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with {%star:%tokens.1, %condition:%tokens.2, %action:%tokens.3}
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assume ((%star and (%star.type is "Word")) and (%star.value is "*")) or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*'
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assume %condition or barf ".."
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Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"
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if: %action is (nil)
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr))"
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do next %func_call
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if: (%condition.type is "Word") and (%condition.value is "else")
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assume (not %is_first) or barf "'else' clause cannot be first in 'when % = ?' block"
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to %code write "\nelse\n "
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to %code write: %action as lua statements
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..else
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assume (not %seen_else) or barf "'else' clause needs to be last in 'when % = ?' block"
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to %code write "\("if" if %is_first else "\nelseif") "
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lua> "table.insert(\%fallthroughs, \(%condition as lua expr));"
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for %i = % in %fallthroughs
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if: %i > 1
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to %code write " or "
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if: (%.type is "Text") or (%.type is "Number")
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to %code write "branch_value == \%"
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..else
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to %code write "utils.equivalent(branch_value, \%)"
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to %code write "then\n "
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to %code write (%action as lua statements)
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%fallthroughs <- []
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%is_first <- (no)
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assume (%fallthroughs = []) or barf "Unfinished fallthrough conditions in 'when' block"
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assume ((length of %code) > 0) or barf "No body for 'when % = ?' block!"
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to %code write "\nend"
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%code <-
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Lua ".."
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do --when % = ?
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local branch_value = \(%branch_value as lua expr);
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\%code
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end --when % = ?
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return %code
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# Try/except
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immediately
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compile [..]
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try %action and if it succeeds %success or if it barfs %fallback
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try %action and if it barfs %fallback or if it succeeds %success
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..to
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Lua ".."
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do
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local fell_through = false;
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local ok, ret = pcall(function()
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\(%action as lua statements)
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fell_through = true;
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end);
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if ok then
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\(%success as lua statements)
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end
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if not ok then
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\(%fallback as lua statements)
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elseif not fell_through then
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return ret;
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end
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end
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parse [try %action] as
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try %action and if it succeeds: do nothing
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..or if it barfs: do nothing
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parse [try %action and if it barfs %fallback] as
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try %action and if it succeeds: do nothing
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..or if it barfs %fallback
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parse [try %action and if it succeeds %success] as
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try %action and if it succeeds %success or if it barfs: do nothing
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# Do/finally
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immediately
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compile [do %action] to
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Lua ".."
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do
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\(%action as lua statements)
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end --do
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compile [do %action then always %final_action] to
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Lua ".."
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do
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local fell_through = false;
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local ok, ret1 = pcall(function()
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\(%action as lua statements)
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fell_through = true;
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end);
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local ok2, ret2 = pcall(function()
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\(%final_action as lua statements)
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end);
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if not ok then error(ret1); end
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if not ok2 then error(ret2); end
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if not fell_through then
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return ret1;
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end
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end --do-then-always
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