GeneratedExpressions.jl:
Expression Comprehensions in Julia

About | Context | Features | Showcase | Documentation

About

The package implements a metalanguage to support code-less expression comprehensions in Julia.

In particular, we provide a convenient proxy (inspired by mustache.js's notation) which takes an expression (string, alternatively), interpolates the $s in the expressions from ranges provided at the input, and then amalgamates the generated expressions into a block, a tuple, etc.

It is possible to retrieve the generated expression (function generate) or to evaluate the expression in the caller's scope on the fly (macro @generate, @fileval).

Context: Dynamics of Value Evolution (DyVE)

The package is an integral part of the Dynamics of Value Evolution (DyVE) computational framework for learning, designing, integrating, simulating, and optimizing R&D process models, to better inform strategic decisions in science and business.

As the framework evolves, multiple functionalities have matured enough to become standalone packages.

This includes ReactiveDynamics.jl, a package which implements a category of reaction (transportation) network-type dynamical systems. The central concept of the package is of a stateful, parametric transition; simultaneous action of the transitions then evolves the dynamical system. Moreover, a network's dynamics can be specified using a compact modeling metalanguage.

Another package is AlgebraicAgents.jl, a lightweight package to enable hierarchical, heterogeneous dynamical systems co-integration. It implements a highly scalable, fully customizable interface featuring sums and compositions of dynamical systems. In present context, we note it can be used to co-integrate a reaction network problem with, e.g., a stochastic ordinary differential problem!

Features

At the input is a general expression with (nested) expression comprehension atoms of the form {<expression body>, <substitution ranges>, <local generator opts>}. The substitution ranges yield an iterator over substitution choices; by default, this is a product over the ranges and the ranges are evaluated in a sequential order from left to right. Use zip=true within <local generator opts> to zip the iterators instead (Julia's standard zipping behavior).

For each substitution choice, expressions of the from $sym within <expression body> are substituted with the respective choices (otherwise left unchanged). The resulting vector of expressions is either wrapped into 1) a block expression or 2) a call expression. In the latter case, the function's name is specified in dlm=<call name>; additionally, dlm=:(=) is supported as well.

Note that in the above process, the substitution happens at the expression level. It is likewise possible to input a string, perform string substitutions according to rules described above, and parse the resulting string into an expression. Because of the internal parsing, an expression body containing a comma has to be escaped by another pair of angle brackets (< and >).

In addition, both function and macro forms accept top-level generation opts: you may 1) provide singular substitution ranges with global effect (interpolates corresponding $syms within the expression at the input) and 2) evaluate the macros before returning the expression (the usecase is bound to the function form).

Showcase

Function form: retrieve generated expression

julia> generate("{\$a+\$b, a=1:2, b=1:2}") |> println
1+1
1+2
2+1
2+2

julia> generate("{\$a+\$b, a=1:2, b=1:2, zip=true}") |> println
1+1
2+2

julia> generate("{<\$a+{\$b, b=1:\$a, dlm=+}>, a=1:2}") |> println
1+1
2+1+2

julia> generate("{<\$a+{<\$b+{\$c, c=1:(\$a+\$b), dlm=+}>, b=1:\$a, dlm=+}>, a=1:2}") |> println
1+1+1+2
2+1+1+2+3+2+1+2+3+4

julia> generate("""{\$a, a=["str_\$c" for c in 1:2], dlm=" "}""") |> println
str_1 str_2

Macro form: evaluate generated expression

julia> @generate {$a+$b, a=1:3, b=1:2, zip=true, dlm=+}
6

julia> @generate {$a+$b, a=1:3, b=1:$a, dlm=+}
24

julia> N=2; @generate "{<\$a+\$b+\$r>, a=1:3, b=1:\$a, r=N, dlm=+}"
36

julia> a=b=c=1; @generate("{<\$[a,b,c]>, dlm=+}")
3

julia> write("file_expr.jl", """{println(\$your_name, ", that is ", \$name), name=["bot_\$i" for i in 1:2]}""")
72

julia> @fileval file_expr.jl your_name="myself"
myself, that is bot_1
myself, that is bot_2

julia> write("file_string.jl", """{<println("\$your_name, that is \$name")>, name=["bot_\$i" for i in 1:2]}""")
70

julia> @fileval file_string.jl mode=string your_name="myself"
myself, that is bot_1
myself, that is bot_2