DiagrammeR(diagram = "", type = "mermaid", ...)

## Not run: 
# note the whitespace is not important
DiagrammeR("
  graph LR
    A-->B
    A-->C
    C-->E
    B-->D
    C-->D
    D-->F
    E-->F
")

DiagrammeR("
   graph TB
   A-->B
   A-->C
   C-->E
   B-->D
   C-->D
   D-->F
   E-->F
")

DiagrammeR("graph LR;A(Rounded)-->B[Squared];B-->C{A Decision};
 C-->D[Square One];C-->E[Square Two];
 style A fill:#E5E25F;  style B fill:#87AB51; style C fill:#3C8937;
 style D fill:#23772C;  style E fill:#B6E6E6;"
)

# Load in the 'mtcars' dataset
data(mtcars)
connections <- sapply(
 1:ncol(mtcars)
  ,function(i) {
     paste0(
        i
      ,"(",colnames(mtcars)[i],")---"
      ,i,"-stats("
      ,paste0(
        names(summary(mtcars[,i]))
        ,": "
        ,unname(summary(mtcars[,i]))
        ,collapse="<br/>"
      )
      ,")"
   )
 }
)

DiagrammeR(
   paste0(
     "graph TD;", "\n",
     paste(connections, collapse = "\n"),"\n",
     "classDef column fill:#0001CC, stroke:#0D3FF3, stroke-width:1px;" ,"\n",
     "class ", paste0(1:length(connections), collapse = ","), " column;"
   )
 )

# also with DiagrammeR() you can use tags from htmltools
# just make sure to use class = "mermaid"
library(htmltools)
diagramSpec = "
graph LR;
  id1(Start)-->id2(Stop);
  style id1 fill:#f9f,stroke:#333,stroke-width:4px;
  style id2 fill:#ccf,stroke:#f66,stroke-width:2px,stroke-dasharray: 5, 5;
"
html_print(tagList(
  tags$h1("R + mermaid.js = Something Special")
  ,tags$pre(diagramSpec)
  ,tags$div(class="mermaid",diagramSpec)
  ,DiagrammeR()
))

# sequence diagrams
# Using this "How to Draw a Sequence Diagram"
#   http://www.cs.uku.fi/research/publications/reports/A-2003-1/page91.pdf
# draw some sequence diagrams with DiagrammeR

library(DiagrammeR)

DiagrammeR("
sequenceDiagram;
   customer->>ticket seller: ask for ticket;
   ticket seller->>database: seats;
   alt tickets available
     database->>ticket seller: ok;
     ticket seller->>customer: confirm;
     customer->>ticket seller: ok;
     ticket seller->>database: book a seat;
     ticket seller->>printer: print ticket;
   else sold out
     database->>ticket seller: none left;
     ticket seller->>customer:  sorry;
   end
")

## End(Not run)