Implemented FrAngel on feat/frangel (#7)

* Add skeleton for frangel

* Add FrAngel draft

* Add FrAngel utils

* Add frangel implementatin, missing tests

* Add FrAngel tests

* Update src/frangel/method.jl

Co-authored-by: Reuben Gardos Reid <[email protected]>

* Update src/frangel/method.jl

Co-authored-by: Reuben Gardos Reid <[email protected]>

* Fixes from review

* Drop 1.8 testing in CI

---------

Co-authored-by: Reuben Gardos Reid <[email protected]>

.dev/Project.toml

@@ -1,2 +1,3 @@
 [deps]
+Git = "d7ba0133-e1db-5d97-8f8c-041e4b3a1eb2"
 JuliaFormatter = "98e50ef6-434e-11e9-1051-2b60c6c9e899"

.github/workflows/CI.yml

@@ -24,8 +24,7 @@ jobs:
       matrix:
         version:
           - '1.10'
-          - '1.8'
-          - 'pre'
+          - '1'
         os:
           - ubuntu-latest
         arch:

Project.toml

@@ -2,5 +2,11 @@ name = "Garden"
 uuid = "22d0bc84-1826-4aaf-b584-c2a6a91114a2"
 version = "0.1.0"
 
+[deps]
+DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
+Herb = "c09c6b7f-4f63-49de-90d9-97a3563c0f4a"
+
 [compat]
+DocStringExtensions = "0.9.3"
+Herb = "0.4.1"
 julia = "^1.8"

src/Garden.jl

@@ -1,5 +1,9 @@
 module Garden
 
-greet() = print("Hello World!")
+using DocStringExtensions
+
+include("frangel/method.jl")
+
+export FrAngel
 
 end # module Garden

src/frangel/README.md

@@ -0,0 +1,17 @@
+# FrAngel
+
+[Publication (Open Access)](https://doi.org/10.1145/3290386)
+
+```
+@article{DBLP:journals/pacmpl/ShiSL19,
+  author       = {Kensen Shi and
+                  Jacob Steinhardt and
+                  Percy Liang},
+  title        = {FrAngel: component-based synthesis with control structures},
+  journal      = {Proc. {ACM} Program. Lang.},
+  volume       = {3},
+  number       = {{POPL}},
+  pages        = {73:1--73:29},
+  year         = {2019}
+}
+```

src/frangel/method.jl

@@ -0,0 +1,245 @@
+module FrAngel
+
+using DocStringExtensions
+using Herb.HerbCore: AbstractRuleNode, AbstractGrammar, get_rule, isfilled, depth
+using Herb.HerbSpecification: AbstractSpecification, Problem
+using Herb.HerbSearch: ProgramIterator, evaluate
+using Herb.HerbInterpret: SymbolTable
+using Herb.HerbConstraints: get_grammar, freeze_state
+using Herb.HerbGrammar: ContextSensitiveGrammar, grammar2symboltable, rulenode2expr,
+                        isterminal, iscomplete, add_rule!
+
+@enum SynthResult optimal_program=1 suboptimal_program=2
+
+struct NoProgramFoundError <: Exception
+    message::String
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Synthesize a program using the `grammar` that follows the `spec` following the method from 
+["FrAngel: component-based synthesis with control structures"](https://doi.org/10.1145/3290386).
+
+!!! note
+
+    This implementation includes fragment mining but *excludes angelic conditions*!
+
+Constructs an iterator of type `iterator_type`. Iteratively, collects promising programs, mines fragments from them and adds them to the grammar. 
+This is then re-started with the updated grammar.
+
+- `frangel_iterations` determines how many iterations of search are run
+- `max_iterations` puts a bound on how many programs should be enumerated within one search procedure.
+- `max_iteration_time` limits the time the iterator has for each search. Note that this time is only checked whenever a program is iterated and thus may take slightly longer than the given time.
+```
+"""
+function frangel(
+        iterator_type::Type{T},
+        grammar::AbstractGrammar,
+        starting_sym::Symbol,
+        problem::Problem;
+        max_iterations::Int = typemax(Int),
+        frangel_iterations::Int = 3,
+        max_iteration_time::Int = typemax(Int),
+        kwargs...
+)::Union{AbstractRuleNode, Nothing} where {T <: ProgramIterator}
+    # FrAngel config arguments
+
+    for _ in 1:frangel_iterations
+        # Gets an iterator with some limit (the low-level budget)
+        iterator = iterator_type(grammar, starting_sym; kwargs...)
+
+        # Run a budgeted search
+        promising_programs, result_flag = get_promising_programs(
+            iterator, problem; max_time = max_iteration_time,
+            max_enumerations = max_iterations)
+
+        if result_flag == optimal_program
+            return only(promising_programs) # returns the only element
+        end
+
+        # Throw an error if no programs were found.
+        if length(promising_programs) == 0
+            throw(NoProgramFoundError("No promising program found for the given specification. Try exploring more programs."))
+        end
+
+        # Extract fragments
+        fragments = mine_fragments(grammar, promising_programs)
+
+        # Select fragments that should be added to the gramamr
+        selected_fragments = select_fragments(fragments)
+
+        # Modify grammar
+        modify_grammar_frangel!(selected_fragments, grammar)
+    end
+
+    @warn "No solution found. Within $frangel_iterations iterations."
+    return nothing
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Decide whether to keep a program, or discard it, based on the specification.
+Returns a score where score=1 yields the program immediately.
+"""
+function decide_frangel(
+        program::AbstractRuleNode,
+        problem::Problem,
+        grammar::ContextSensitiveGrammar,
+        symboltable::SymbolTable
+)
+    expr = rulenode2expr(program, grammar)
+    score = evaluate(problem, expr, symboltable, shortcircuit = false)
+    return score
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Modify the grammar based on the fragments mined from the programs kept during the `decide` step.
+This function adds "Fragment_{type}" to the grammar to denote added fragments.
+"""
+function modify_grammar_frangel!(
+        fragments::AbstractVector{<:AbstractRuleNode},
+        grammar::AbstractGrammar;
+        max_fragment_rules::Int = typemax(Int)
+)
+    for f in fragments
+        ind = get_rule(f)
+        type = grammar.types[ind]
+        frag_type = Symbol("Fragment_", type)
+
+        # Add fragment_{type} to the grammar if not present yet
+        if !haskey(grammar.bytype, frag_type)
+            #@TODO substitute fragment rules
+            add_rule!(grammar, Meta.parse("$type = $frag_type"))
+        end
+
+        expr = rulenode2expr(f, grammar)
+        add_rule!(grammar, Meta.parse("$frag_type = $expr"))
+    end
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Selects the smallest (fewest number of nodes) fragments from the set of mined fragments. 
+`num_programs` determines how many programs should be selected.
+"""
+function select_smallest_fragments(
+        fragments::Set{AbstractRuleNode};
+        num_programs::Int = 3
+)::AbstractVector{<:AbstractRuleNode}
+    sorted_nodes = sort(collect(fragments), by = x -> length(x))
+
+    # Select the top 3 elements
+    return sorted_nodes[1:min(num_programs, length(sorted_nodes))]
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Selects the shallowest (smallest depth) fragments from the set of mined fragments. 
+`num_programs` determines how many programs should be selected.
+"""
+function select_shallowest_fragments(
+        fragments::Set{AbstractRuleNode};
+        num_programs::Int = 3
+)::AbstractVector{<:AbstractRuleNode}
+    sorted_nodes = sort(collect(fragments), by = x -> depth(x))
+
+    # Select the top 3 elements
+    return sorted_nodes[1:min(num_programs, length(sorted_nodes))]
+end
+
+function select_fragments(fragments::Set{AbstractRuleNode})
+    select_smallest_fragments(fragments; num_programs = 3)
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Iterates over the solutions to find partial or full solutions.
+Takes an iterator to enumerate programs. Quits when `max_time` or `max_enumerations` is reached.
+If the program solves the problem, it is returned with the `optimal_program` flag.
+If a program solves some of the problem (e.g. some but not all examples) it is added to the list of `promising_programs`.
+The set of promising programs is returned eventually.
+"""
+function get_promising_programs(
+        iterator::ProgramIterator,
+        problem::Problem;
+        max_time = typemax(Int),
+        max_enumerations = typemax(Int),
+        mod::Module = Main
+)::Tuple{Set{AbstractRuleNode}, SynthResult}
+    start_time = time()
+    grammar = get_grammar(iterator.solver)
+    symboltable::SymbolTable = grammar2symboltable(grammar, mod)
+
+    promising_programs = Set{AbstractRuleNode}()
+
+    for (i, candidate_program) in enumerate(iterator)
+        score = decide_frangel(candidate_program, problem, grammar, symboltable)
+
+        if score == 1
+            push!(promising_programs, freeze_state(candidate_program))
+            return (promising_programs, optimal_program)
+        elseif score > 0
+            push!(promising_programs, freeze_state(candidate_program))
+        end
+
+        # Check stopping criteria
+        if i > max_enumerations || time() - start_time > max_time
+            break
+        end
+    end
+
+    return (promising_programs, suboptimal_program)
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Finds all the fragments from the `program` defined over the `grammar`.
+
+The result is a set of the distinct program fragments, generated recursively by iterating over all children. A fragment is any complete subprogram of the original program.
+
+"""
+function mine_fragments(
+        grammar::AbstractGrammar, program::AbstractRuleNode)::Set{AbstractRuleNode}
+    fragments = Set{AbstractRuleNode}()
+    # Push terminals as they are
+    if isfilled(program) && !isterminal(grammar, program)
+        # Only complete programs count are considered
+        if iscomplete(grammar, program)
+            push!(fragments, program)
+        end
+        for child in program.children
+            fragments = union(fragments, mine_fragments(grammar, child))
+        end
+    end
+
+    return fragments
+end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Finds fragments (subprograms) of each program in `programs`.
+"""
+function mine_fragments(
+        grammar::AbstractGrammar, programs::Set{<:AbstractRuleNode})::Set{AbstractRuleNode}
+    fragments = reduce(union, mine_fragments(grammar, p) for p in programs)
+    fragments = setdiff(fragments, programs) # Don't include the programs themselves in the set of fragments
+
+    return fragments
+end
+
+export
+       frangel,
+       decide_frangel,
+       modify_grammar_frangel!,
+       get_promising_programs
+
+end

src/frangel/ref.bib

@@ -0,0 +1,11 @@
+@article{DBLP:journals/pacmpl/ShiSL19,
+  author       = {Kensen Shi and
+                  Jacob Steinhardt and
+                  Percy Liang},
+  title        = {FrAngel: component-based synthesis with control structures},
+  journal      = {Proc. {ACM} Program. Lang.},
+  volume       = {3},
+  number       = {{POPL}},
+  pages        = {73:1--73:29},
+  year         = {2019}
+}

test/Project.toml

@@ -1,4 +1,5 @@
 [deps]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
+Herb = "c09c6b7f-4f63-49de-90d9-97a3563c0f4a"
 JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

test/runtests.jl

@@ -10,5 +10,9 @@ using JET
     @testset "Code linting (JET.jl)" begin
         JET.test_package(Garden; target_defined_modules = true)
     end
-    # Write your tests here.
+    for (root, dirs, files) in walkdir(@__DIR__)
+        for file in filter(contains(r"test_"), files)
+            include(file)
+        end
+    end
 end