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21_Translating_R_code.Rmd
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21_Translating_R_code.Rmd
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# Translating R code
**Learning objectives:**
- Build DSL (domain specific languages) to aid interoperability between R, HTML and LaTeX
- Reinforce metaprogramming concepts (expressions, quasiquotation, evaluation)
```{r, echo = FALSE, eval = TRUE}
DiagrammeR::mermaid("
graph LR
expressions --> R
quasiquotation --> R
evaluation --> R
R --> HTML
R --> LaTeX
")
```
<details>
<summary>Mermaid code</summary>
```{r, echo = TRUE, eval = FALSE}
DiagrammeR::mermaid("
graph LR
expressions --> R
quasiquotation --> R
evaluation --> R
R --> HTML
R --> LaTeX
")
```
</details>
<details>
<summary>Session Info</summary>
```{r, message = FALSE, warning = FALSE}
library(DiagrammeR) #for Mermaid flowchart
library(lobstr) #abstract syntax trees
library(purrr) #functional programming
library(rlang) #tidy evaluation
# from section 18.5
expr_type <- function(x) {
if (rlang::is_syntactic_literal(x)) {
"constant"
} else if (is.symbol(x)) {
"symbol"
} else if (is.call(x)) {
"call"
} else if (is.pairlist(x)) {
"pairlist"
} else {
typeof(x)
}
}
flat_map_chr <- function(.x, .f, ...) {
purrr::flatten_chr(purrr::map(.x, .f, ...))
}
switch_expr <- function(x, ...) {
switch(expr_type(x),
...,
stop("Don't know how to handle type ", typeof(x), call. = FALSE)
)
}
```
```{r}
utils::sessionInfo()
```
</details>
## Case Study: MCQ
We are going to use R code to generate HTML or LaTeX to produce multiple-choice questions such as
### Pop Quiz!
1. What is the **derivative** of $f(x) = 1 + 2\cos(3\pi x + 4)$?
a. $f'(x) = 6\pi\sin(3\pi x + 4)$
b. $f'(x) = -6\pi\sin(3\pi x + 4)$
c. $f'(x) = 24\pi\sin(3\pi x + 4)$
d. $f'(x) = -24\pi\sin(3\pi x + 4)$
---
As developers, we may be asking ourselves:
* What are the expressions?
* What are the symbols?
* Will we have to quote inputs from the user (math teacher)?
## HTML
We are trying to produce
```{}
<body>
<h1 id = 'pop_quiz'>Pop Quiz</h1>
<ol>
<li>What is the <b>derivative</b> of $f(x) = 1 + 2\cos(3\pi x + 4)$?</li>
<ol>
<li>$f'(x) = 6\pi\sin(3\pi x + 4)$</li>
<li>$f'(x) = -6\pi\sin(3\pi x + 4)$</li>
<li>$f'(x) = 24\pi\sin(3\pi x + 4)$</li>
<li>$f'(x) = -24\pi\sin(3\pi x + 4)$</li>
</ol>
</ol>
<img src = 'calculus_cat.png' width = '100' height = '100' />
</body>
```
using DSL
```{r, eval = FALSE}
with_html(
body(
h1("Pop quiz!", id = "pop_quiz"),
ol(
li("What is the ", b("derivative"), "of $f(x) = 1 + 2cos(3pi x + 4)$?"),
ol(
li("$f'(x) = 6pi*sin(3pi x + 4)$"),
li("$f'(x) = -6pi*sin(3pi x + 4)$"),
li("$f'(x) = 24pi*sin(3pi x + 4)$"),
li("$f'(x) = -24pi*sin(3pi x + 4)$")
)
),
img(src = "images/translating/calculus_cat.png", width = 100, height = 100)
)
)
```
In particular,
* **tags** such as `<b></b>` have *attributes*
* **void tags** such as `<img />`
* special characters: `&`, `<`, and `>`
<details>
<summary>HTML verification</summary>
```{=html}
<body>
<h1 id = 'pop_quiz'>Pop Quiz</h1>
<ol>
<li>What is the <b>derivative</b> of $f(x) = 1 + 2\cos(3\pi x + 4)$?</li>
<ol>
<li>$f'(x) = 6\pi\sin(3\pi x + 4)$</li>
<li>$f'(x) = -6\pi\sin(3\pi x + 4)$</li>
<li>$f'(x) = 24\pi\sin(3\pi x + 4)$</li>
<li>$f'(x) = -24\pi\sin(3\pi x + 4)$</li>
</ol>
</ol>
<img src = 'images/translating/calculus_cat.png' width = '100' height = '100' />
</body>
```
</details>
## Escaping
* need to escape `&`, `<`, and `>`
* don't "double escape"
* leave HTML alone
### S3 Class
```{r}
html <- function(x) structure(x, class = "advr_html")
#dispatch
print.advr_html <- function(x, ...) {
out <- paste0("<HTML> ", x)
cat(paste(strwrap(out), collapse = "\n"), "\n", sep = "")
}
```
### Generic
```{r}
escape <- function(x) UseMethod("escape")
escape.character <- function(x) {
x <- gsub("&", "&", x)
x <- gsub("<", "<", x)
x <- gsub(">", ">", x)
html(x)
}
escape.advr_html <- function(x) x
```
### Checks
```{r}
escape("This is some text.")
escape("x > 1 & y < 2")
escape(escape("This is some text. 1 > 2")) #double escape
escape(html("<hr />")) #already html
```
## Named Components
```{}
li("What is the ", b("derivative"), "of $f(x) = 1 + 2\cos(3\pi x + 4)$?")
```
* aiming to classify `li` and `b` as **named components**
```{r}
dots_partition <- function(...) {
dots <- list2(...)
if (is.null(names(dots))) {
is_named <- rep(FALSE, length(dots))
} else {
is_named <- names(dots) != ""
}
list(
named = dots[is_named],
unnamed = dots[!is_named]
)
}
```
### Check
```{r}
str(dots_partition(company = "Posit",
software = "RStudio",
"DSLC",
"Cohort 9"))
```
<details>
<summary>HTML Attributes</summary>
Found among the textbook's [source code](https://github.com/hadley/adv-r/blob/master/dsl-html-attributes.r)
```{r}
html_attributes <- function(list) {
if (length(list) == 0) return("")
attr <- map2_chr(names(list), list, html_attribute)
paste0(" ", unlist(attr), collapse = "")
}
html_attribute <- function(name, value = NULL) {
if (length(value) == 0) return(name) # for attributes with no value
if (length(value) != 1) stop("`value` must be NULL or length 1")
if (is.logical(value)) {
# Convert T and F to true and false
value <- tolower(value)
} else {
value <- escape_attr(value)
}
paste0(name, "='", value, "'")
}
escape_attr <- function(x) {
x <- escape.character(x)
x <- gsub("\'", ''', x)
x <- gsub("\"", '"', x)
x <- gsub("\r", ' ', x)
x <- gsub("\n", ' ', x)
x
}
```
</details>
## Tags (calls)
```{r}
tag <- function(tag) {
new_function(
exprs(... = ), #arguments of new function
expr({ #body of the new function
#classify tags as named components
dots <- dots_partition(...)
#focus on named components as the tags
attribs <- html_attributes(dots$named)
# otherwise, nested code
children <- map_chr(dots$unnamed, escape)
# paste brackets, tag names, and attributes together
# then unquote user arguments
html(paste0(
!!paste0("<", tag), attribs, ">",
paste(children, collapse = ""),
!!paste0("</", tag, ">")
))
}),
caller_env() #return the environment
)
}
```
<details>
<summary>Void tags</summary>
```{r}
void_tag <- function(tag) {
new_function(
exprs(... = ), #allows for missing arguments
expr({
dots <- dots_partition(...)
# error check
if (length(dots$unnamed) > 0) {
abort(!!paste0("<", tag, "> must not have unnamed arguments"))
}
attribs <- html_attributes(dots$named)
html(paste0(!!paste0("<", tag), attribs, " />"))
}),
caller_env()
)
}
```
</details>
### Checks
```{r}
tag("ol")
```
```{r}
img <- void_tag("img")
```
```{r, error = TRUE, results = "asis"}
img()
```
```{r}
img(src = "images/translating/calculus_cat.png",
width = 100,
height = 100)
```
## Tags (processing)
<details>
<summary>Venn Diagram</summary>
```{r}
tags <- c("a", "abbr", "address", "article", "aside", "audio",
"b","bdi", "bdo", "blockquote", "body", "button", "canvas",
"caption","cite", "code", "colgroup", "data", "datalist",
"dd", "del","details", "dfn", "div", "dl", "dt", "em",
"eventsource","fieldset", "figcaption", "figure", "footer",
"form", "h1", "h2", "h3", "h4", "h5", "h6", "head", "header",
"hgroup", "html", "i","iframe", "ins", "kbd", "label",
"legend", "li", "mark", "map","menu", "meter", "nav",
"noscript", "object", "ol", "optgroup", "option", "output",
"p", "pre", "progress", "q", "ruby", "rp","rt", "s", "samp",
"script", "section", "select", "small", "span", "strong",
"style", "sub", "summary", "sup", "table", "tbody", "td",
"textarea", "tfoot", "th", "thead", "time", "title", "tr",
"u", "ul", "var", "video"
)
void_tags <- c("area", "base", "br", "col", "command", "embed",
"hr", "img", "input", "keygen", "link", "meta", "param",
"source", "track", "wbr"
)
```
</details>
```{r}
html_tags <- c(
tags |> #list of tag names from HTML
set_names() |> #named variable to avoid reserved words!
map(tag), #make them function calls
void_tags |>
set_names() |>
map(void_tag)
)
```
### Example
```{r}
html_tags$ol(
html_tags$li("What is the ",
html_tags$b("derivative"),
"of $f(x) = 1 + 2cos(3pi x + 4)$?"))
```
## Bringing the HTML Together
```{r}
with_html <- function(code) {
eval_tidy(enquo(code), html_tags)
}
```
### Main Example
```{r}
with_html(
body(
h1("Pop quiz!", id = "pop_quiz"),
ol(
li("What is the ", b("derivative"), "of $f(x) = 1 + 2cos(3pi x + 4)$?"),
ol(
li("$f'(x) = 6pi*sin(3pi x + 4)$"),
li("$f'(x) = -6pi*sin(3pi x + 4)$"),
li("$f'(x) = 24pi*sin(3pi x + 4)$"),
li("$f'(x) = -24pi*sin(3pi x + 4)$")
)
),
img(src = "images/translating/calculus_cat.png", width = 100, height = 100)
)
)
```
### Check
```{=html}
<h1 id='pop_quiz'>Pop quiz!</h1><ol><li>What is the <b>derivative</b> of $f(x) = 1 + 2cos(3pi x + 4)$?</li><ol><li>$f'(x) = 6pi*sin(3pi x + 4)$</li><li>$f'(x) = -6pi*sin(3pi x + 4)$</li><li>$f'(x) = 24pi*sin(3pi x + 4)$</li><li>$f'(x) = -24pi*sin(3pi x + 4)$</li></ol></ol><img src='images/translating/calculus_cat.png' width='100' height='100' />
```
## LaTeX
```{r}
latex <- function(x) structure(x, class = "advr_latex")
print.advr_latex <- function(x) { cat("<LATEX> ", x, "\n", sep = "") }
```
### to_math
```{r, eval = FALSE}
to_math <- function(x) {
expr <- enexpr(x)
latex( #return LaTeX code
eval_bare( #eval_bare to ensure use of latex environment
expr, #expression (not quosure)
latex_env(expr) #need to define latex_env
))
}
```
## Known Symbols
```{r}
greek_letters <- c(
"alpha", "beta", "chi", "delta", "Delta", "epsilon", "eta",
"gamma", "Gamma", "iota", "kappa", "lambda", "Lambda", "mu",
"nu", "omega", "Omega", "phi", "Phi", "pi", "Pi", "psi", "Psi",
"rho", "sigma", "Sigma", "tau", "theta", "Theta", "upsilon",
"Upsilon", "varepsilon", "varphi", "varrho", "vartheta", "xi",
"Xi", "zeta"
)
greek_env <- rlang::as_environment(
rlang::set_names(
paste0("\\", greek_letters), #latex values
greek_letters #R names
)
)
```
```{r}
str(as.list(greek_env))
```
## Known Functions
### Unary Operations
```{r}
unary_op <- function(left, right) {
new_function(
exprs(e1 = ),
expr(
paste0(!!left, e1, !!right)
),
caller_env()
)
}
```
```{r}
#example
unary_op("\\sqrt{", "}")
```
### Binary Operations
```{r}
binary_op <- function(sep) {
new_function(
exprs(e1 = , e2 = ),
expr(
paste0(e1, !!sep, e2)
),
caller_env()
)
}
```
```{r}
#example
binary_op("+")
```
<details>
<summary>Even more LaTeX syntax</summary>
```{r}
known_func_env <- child_env(
.parent = empty_env(),
# Binary operators
`+` = binary_op(" + "),
`-` = binary_op(" - "),
`*` = binary_op(" * "),
`/` = binary_op(" / "),
`^` = binary_op("^"),
`[` = binary_op("_"),
# Grouping
`{` = unary_op("\\left{ ", " \\right}"),
`(` = unary_op("\\left( ", " \\right)"),
paste = paste,
# Other math functions
sqrt = unary_op("\\sqrt{", "}"),
sin = unary_op("\\sin(", ")"),
cos = unary_op("\\cos(", ")"),
tan = unary_op("\\tan(", ")"),
log = unary_op("\\log(", ")"),
abs = unary_op("\\left| ", "\\right| "),
frac = function(a, b) {
paste0("\\frac{", a, "}{", b, "}")
},
# Labelling
hat = unary_op("\\hat{", "}"),
tilde = unary_op("\\tilde{", "}")
)
```
</details>
## Unknown Symbols
```{r}
names_grabber <- function(x) {
switch_expr(x,
constant = character(),
symbol = as.character(x),
call = flat_map_chr(as.list(x[-1]), names_grabber)
) |>
unique()
}
```
$$x + y + f(a, b, c, 10)$$
```{r}
names_grabber(expr(x + y + f(a, b, c, 10)))
```
```{r}
lobstr::ast(expr(x + y + f(a, b, c, 10)))
```
## Unknown Functions
```{r}
calls_grabber <- function(x) {
switch_expr(x,
constant = ,
symbol = character(),
call = {
fname <- as.character(x[[1]])
children <- flat_map_chr(as.list(x[-1]), calls_grabber)
c(fname, children)
}
) |>
unique()
}
```
$$f(g + b, c, d(a))$$
```{r}
names_grabber(expr(f(g + b, c, d(a))))
calls_grabber(expr(f(g + b, c, d(a))))
lobstr::ast(expr(f(g + b, c, d(a))))
```
---
```{r}
seek_closure <- function(op) {
# change math font for function names
# apply ending parenthesis
new_function(
exprs(... = ),
expr({
contents <- paste(..., collapse = ", ")
paste0(!!paste0("\\mathrm{", op, "}("), contents, ")")
})
)
}
```
## Bringing the LaTeX Together
```{r}
latex_env <- function(expr) {
# Unknown Functions
calls <- calls_grabber(expr)
call_list <- map(set_names(calls), seek_closure)
call_env <- as_environment(call_list)
# Known Functions
known_func_env <- env_clone(known_func_env, call_env)
# Unknown Symbols
names <- names_grabber(expr)
symbol_env <- as_environment(set_names(names), parent = known_func_env)
# Known symbols
greek_env <- env_clone(greek_env, parent = symbol_env)
greek_env
}
to_math <- function(x) {
expr <- enexpr(x)
latex( #return LaTeX code
eval_bare( #eval_bare to ensure use of latex environment
expr, #expression (not quosure)
latex_env(expr) #need to define latex_env
))
}
```
### Check
```{r}
to_math(sin(pi) + f(a))
```
## Finishing the Example
(TO DO)
## Meeting Videos
### Cohort 1
`r knitr::include_url("https://www.youtube.com/embed/fixyitpXrwY")`
`r knitr::include_url("https://www.youtube.com/embed/h3RNPyhIjas")`
### Cohort 2
`r knitr::include_url("https://www.youtube.com/embed/pj0hTW1CtbI")`
### Cohort 3
(no video)
### Cohort 4
`r knitr::include_url("https://www.youtube.com/embed/0TclsXa085Y")`
### Cohort 5
`r knitr::include_url("https://www.youtube.com/embed/v_dkrIEdmKE")`
### Cohort 6
`r knitr::include_url("https://www.youtube.com/embed/_-uwFjO5CyM")`
<details>
<summary> Meeting chat log </summary>
```
00:30:16 Arthur Shaw: https://www.w3schools.com/html/html_entities.asp
00:32:29 Arthur Shaw: Beta symbol in HTML: Β
00:56:55 Arthur Shaw: https://dbplyr.tidyverse.org/articles/translation-function.html
00:57:48 Arthur Shaw: https://dtplyr.tidyverse.org/index.html
00:58:43 Arthur Shaw: https://dtplyr.tidyverse.org/articles/translation.html
```
</details>