rudimentary equation support (sub/superscripts, elimination of dollar signs)

src/latex.jl

@@ -14,6 +14,8 @@ const BRACEOPEN = UInt8('{')
 const BRACECLOSE = UInt8('}')
 const SPACE = UInt8(' ')
 const DOLLAR = UInt8('$')
+const CARET = UInt8('^')
+const UNDERSCORE = UInt8('_')
 isalpha8(x::UInt8) = UInt8('a') ≤ x ≤ UInt8('z') || UInt8('A') ≤ x ≤ UInt8('Z')
 isalnum8(x::UInt8) = UInt8('0') ≤ x ≤ UInt8('9') || isalpha8(x)
 
@@ -33,14 +35,16 @@ function search_latexdirective(s::Union{String,SubString{String}}, istart::Int=1
     allspaces=true
 
     # find \foo directive or {...}:
+    c = UInt8(0)
     while i ≤ e
         c = unsafe_load(p, i)
-        (c == BACKSLASH || c == BRACEOPEN) && break
+        (c == BACKSLASH || c == BRACEOPEN || c == CARET || c == UNDERSCORE) && break
         c != SPACE && (allspaces = false)
         i += 1
     end
-    if i ≤ e && unsafe_load(p, i) == BACKSLASH
+    if i ≤ e && c != BRACEOPEN
         directive_start = i
+        if c == BACKSLASH
             i += 2
             i-1 > e && return 0,0,0
             if isalpha8(unsafe_load(p, i-1))
@@ -49,6 +53,10 @@ function search_latexdirective(s::Union{String,SubString{String}}, istart::Int=1
                 end
             end
             directive_end = i-1
+        else
+            directive_end = directive_start # ^ or _
+            i += 1
+        end
 
         # look for optional opening brace
         while i ≤ e && unsafe_load(p, i) == SPACE
@@ -63,20 +71,28 @@ function search_latexdirective(s::Union{String,SubString{String}}, istart::Int=1
                 j -= 1
             end
             if j < istart || unsafe_load(p, j) != BRACEOPEN
-                # argument is not in braces … get next token
-                if allspaces
+                if unsafe_load(p, i) == BACKSLASH
+                    # argument is another latex directive
+                    ds,de,ae = search_latexdirective(s, i)
+                    return directive_start, directive_end, ae
+                elseif c != BACKSLASH
+                    # in an equation, token is a single char
+                    return directive_start, directive_end, i
+                elseif allspaces
                     # if `\directive ...` was preceded only
                     # by whitespace, then assume arguments
                     # extend to the end of the string.  This
                     # happens when we recurse on `{\directive ...}`.
                     return directive_start, directive_end, e
-                end
+                else
+                    # argument is not in braces … get next token
                     while i ≤ e && isalnum8(unsafe_load(p, i))
                         i += 1
                     end
                     return directive_start, directive_end, i-1
                 end
             end
+        end
         i += 1
     elseif i > e
         return 0,0,0
@@ -173,6 +189,7 @@ const latex_unicode = Dict{String,String}(
     "\\\\" => "\\",
     "\\{" => "{", "\\}" => "}",
     "\\%" => "%",
+    # "\\\$" => "\$" -- dollar signs will be unescaped in strip_dollars
 
     # We parse {....} quoting as an empty directive:
     "" => "#1",
@@ -186,9 +203,12 @@ const md_directives = Dict{String,String}(
     "\\emph" => "_#1_",
     "\\textit" => "_#1_",
     "\\it" => "_#1_",
+    "\\mathit" => "_#1_",
     "\\textbf" => "**#1**",
     "\\bf" => "**#1**",
+    "\\mathbf" => "**#1**",
     "\\texttt" => "`#1`",
+    "\\mathrm" => "#1",
     "\\url" => "[#1](#1)",
     "\\sout" => "~~#1~~",
     "\\st" => "~~#1~~",
@@ -201,15 +221,43 @@ const text_directives = Dict{String,String}(
     "\\emph" => "#1",
     "\\textit" => "#1",
     "\\it" => "#1",
+    "\\mathit" => "#1",
     "\\textbf" => "#1",
     "\\bf" => "#1",
+    "\\mathbf" => "#1",
     "\\texttt" => "#1",
+    "\\mathrm" => "#1",
     "\\url" => "#1",
-    "\\sout" => "#1",
-    "\\st" => "#1",
-    "\\cancel" => "#1",
 )
 
+# Unicode includes an incomplete set of super/subscript characters:
+const superscripts = Dict{Char,Char}(
+    '0'=>'⁰', '1'=>'¹', '2'=>'²', '3'=>'³', '4'=>'⁴', '5'=>'⁵', '6'=>'⁶', '7'=>'⁷', '8'=>'⁸', '9'=>'⁹',
+    'a'=>'ᵃ', 'b'=>'ᵇ', 'c'=>'ᶜ', 'd'=>'ᵈ', 'e'=>'ᵉ', 'f'=>'ᶠ', 'g'=>'ᵍ', 'h'=>'ʰ',
+    'i'=>'ⁱ', 'j'=>'ʲ', 'k'=>'ᵏ', 'l'=>'ˡ', 'm'=>'ᵐ', 'n'=>'ⁿ', 'o'=>'ᵒ', 'p'=>'ᵖ',
+    'r'=>'ʳ', 's'=>'ˢ', 't'=>'ᵗ', 'u'=>'ᵘ', 'v'=>'ᵛ', 'w'=>'ʷ', 'x'=>'ˣ', 'y'=>'ʸ', 'z'=>'ᶻ',
+    'A'=>'ᴬ', 'B'=>'ᴮ', 'C'=>'ᶜ', 'D'=>'ᴰ', 'E'=>'ᴱ', 'G'=>'ᴳ', 'H'=>'ᴴ', 'I'=>'ᴵ', 'J'=>'ᴶ',
+    'K'=>'ᴷ', 'L'=>'ᴸ', 'M'=>'ᴹ', 'N'=>'ᴺ', 'O'=>'ᴼ', 'P'=>'ᴾ', 'R'=>'ᴿ', 'S'=>'ˢ', 'T'=>'ᵀ',
+    'U'=>'ᵁ', 'V'=>'ⱽ', 'W'=>'ᵂ', 'β'=>'ᵝ', 'γ'=>'ᵞ', 'δ'=>'ᵟ', 'ψ'=>'ᵠ', 'χ'=>'ᵡ', 'Θ'=>'ᶿ',
+    '+'=>'⁺', '-'=>'⁻', '='=>'⁼', '('=>'⁽', ')'=>'⁾', ' '=>' ',
+)
+const subscripts = Dict{Char,Char}(
+    '0'=>'₀', '1'=>'₁', '2'=>'₂', '3'=>'₃', '4'=>'₄', '5'=>'₅', '6'=>'₆', '7'=>'₇', '8'=>'₈', '9'=>'₉',
+    'a'=>'ₐ', 'e'=>'ₑ', 'h'=>'ₕ', 'i'=>'ᵢ', 'j'=>'ⱼ', 'k'=>'ₖ', 'l'=>'ₗ', 'm'=>'ₘ',
+    'n'=>'ₙ', 'o'=>'ₒ', 'p'=>'ₚ', 'r'=>'ᵣ', 's'=>'ₛ', 't'=>'ₜ', 'u'=>'ᵤ', 'v'=>'ᵥ', 'x'=>'ₓ',
+    'β'=>'ᵦ', 'γ'=>'ᵧ', 'ρ'=>'ᵨ', 'ψ'=>'ᵩ', 'χ'=>'ᵪ',
+    '-'=>'₋', '+'=>'₊', '='=>'₌', '('=>'₍', ')'=>'₎', ' '=>' ',
+)
+function replacechars(s::AbstractString, charmap::Associative{Char,Char})
+    buf = IOBuffer()
+    for c in s
+        cm = get(charmap, c, '\0')
+        cm == '\0' && return ""
+        print(buf, cm)
+    end
+    return String(take!(buf))
+end
+
 # Given a (sub)string `s` that represents a LaTeX directive matched
 # by search_latexdirective, performs our Unicode substitutions and
 # also any additional substitutions given by extra_directives.
@@ -233,9 +281,43 @@ function directive_substitution(s::AbstractString, extra_directives::Associative
             end
         end
     end
+    if directive == "^" || directive == "_" # super/subscripts
+        arg = striparg(replace_directives(striparg(s, de+1, ae), extra_directives))
+        sarg = replacechars(arg, directive == "^" ? superscripts : subscripts)
+        !isempty(sarg) && return sarg
+    end
     return s # ignore unrecognized directives
 end
 
 # replace all latex directives in `s` via `directive_substitution`
 replace_directives(s::AbstractString, extra_directives::Associative{String,String}) =
     replace(s, LaTeXDirectiveSearch(), sub -> directive_substitution(sub, extra_directives))
+
+# strip unescaped $ signs from s
+function strip_dollars(s::Union{String,SubString{String}})
+    buf = IOBuffer()
+    p = pointer(s)
+    for i = 1:sizeof(s)
+        c = unsafe_load(p, i)
+        if c == BACKSLASH && i < sizeof(s) && unsafe_load(p, i+1) == DOLLAR
+            write(buf, DOLLAR) # \$ -> $
+        elseif c != DOLLAR
+            write(buf, c)
+        end
+    end
+    return String(take!(buf))
+end
+
+"""
+    simplify_latex(s::AbstractString, extra_directives=BibTeX.text_directives)
+
+Simplify a LaTeX string `s` into "plain text" if possible, stripping/converting
+known LaTeX directives in favor of e.g Unicode.
+
+`extra_directives` is a dictionary (`String=>String`) that maps LaTeX directives
+to replacements.  It defaults to `BibTeX.text_directives`, which simply strips
+out things like bold and italics.  Alternatively, you can pass `BibTeX.md_directives`,
+which uses Markdown syntax for such directives.
+"""
+simplify_latex(s::AbstractString, extra_directives::Associative{String,String}=text_directives) =
+    strip_dollars(replace_directives(s, extra_directives))

test/runtests.jl

@@ -48,8 +48,8 @@ end
     @test isempty(sizehint!(empty!(x2),10))
 end
 
-import BibTeX: replace_directives, md_directives
+import BibTeX: simplify_latex, md_directives
 @testset "latex" begin
-    @test replace_directives(raw"foo \dot{\alpha} {quote} \% \{unquote\} \emph{bar \textbf{bold}} {\bf baz 2.0} {\^{u}}", md_directives) ==
-          "foo α̇ quote % {unquote} _bar **bold**_ **baz 2.0** û"
+    @test simplify_latex(raw"foo \$$x_1x_2^\mathrm{3}$ \dot{\alpha} {quote} \% \{unquote\} \emph{bar \textbf{bold}} {\bf baz 2.0} {\^{u}}", md_directives) ==
+          "foo \$x₁x₂³ α̇ quote % {unquote} _bar **bold**_ **baz 2.0** û"
 end