Improve show

src/show.jl

@@ -8,33 +8,110 @@ __prints_with_minus(x::Real) = x < 0
 __needs_parens(::Any) = false
 __needs_parens(a::AlgebraElement) = true
 
-function _coeff_elt_print(io, c, elt)
-    print(io, c, '·')
+# `print_coefficient` is inspired from MultivariatePolynomials.jl
+
+# `Int`, `Float64` don't support MIME"text/latex".
+# We could add a check with `showable` if a `Real` subtype supports it and
+# the feature is requested.
+print_coefficient(io::IO, mime, coeff::Real) = print(io, coeff)
+# Scientific notation does not display well in LaTeX so we rewrite it
+function print_coefficient(io::IO, mime::MIME"text/latex", coeff::AbstractFloat)
+    s = string(coeff)
+    if occursin('e', s)
+        s = replace(s, 'e' => " \\cdot 10^{") * '}'
+    end
+    return print(io, s)
+end
+
+trim_LaTeX(::MIME, s::AbstractString) = s
+
+function trim_LaTeX(::MIME"text/latex", s::AbstractString)
+    i = firstindex(s)
+    j = lastindex(s)
+    while true
+        if i < j && isspace(s[i])
+            i = nextind(s, i)
+        elseif i < j && isspace(s[j])
+            j = prevind(s, j)
+        elseif i < j && s[i] == '$' && s[j] == '$'
+            i = nextind(s, i)
+            j = prevind(s, j)
+        elseif i < j && (
+            (s[i:nextind(s, i)] == "\\(" && s[prevind(s, j):j] == "\\)") ||
+            (s[i:nextind(s, i)] == "\\[" && s[prevind(s, j):j] == "\\]")
+        )
+            i = nextind(s, i, 2)
+            j = prevind(s, j, 2)
+        else
+            return s[i:j]
+        end
+    end
+end
+
+# JuMP expressions supports LaTeX output so `showable` will return `true`
+# for them. It is important for anonymous variables to display properly as well:
+# https://github.com/jump-dev/SumOfSquares.jl/issues/256
+# Since they add `$$` around it, we need to trim it with `trim_LaTeX`
+function print_coefficient(io::IO, mime, coeff)
+    print(io, "(")
+    if showable(mime, coeff)
+        print(io, trim_LaTeX(mime, sprint(show, mime, coeff)))
+    else
+        show(io, coeff)
+    end
+    return print(io, ")")
+end
+
+_print_dot(io, ::MIME"text/latex") = print(io, " \\cdot ")
+_print_dot(io, ::MIME) = print(io, '⋅')
+
+function _coeff_elt_print(io, mime, c, elt)
+    print_coefficient(io, mime, c)
+    _print_dot(io, mime)
     __needs_parens(elt) && print(io, '(')
-    print(io, elt)
+    print(io, trim_LaTeX(mime, sprint(show, mime, elt)))
     __needs_parens(elt) && print(io, ')')
     return
 end
 
-function Base.show(io::IO, a::AlgebraElement)
+Base.print(io::IO, a::AlgebraElement) = show(io, MIME"text/print"(), a)
+Base.show(io::IO, a::AlgebraElement) = show(io, MIME"text/plain"(), a)
+
+function Base.show(io::IO, mime::MIME"text/latex", a::AlgebraElement)
+    print(io, "\$\$ ")
+    _show(io, mime, a)
+    return print(io, " \$\$")
+end
+
+# If the MIME is not specified, IJulia thinks that it supports images, ...
+# and then use the result of show and tries to interpret it as an svg, ...
+# We need the two methods to avoid ambiguity
+function Base.show(io::IO, mime::MIME"text/plain", a::AlgebraElement)
+    return _show(io, mime, a)
+end
+function Base.show(io::IO, mime::MIME"text/print", a::AlgebraElement)
+    return _show(io, mime, a)
+end
+
+function _show(io::IO, mime, a::AlgebraElement)
     A = parent(a)
     if iszero(a)
         T = valtype(coeffs(a))
-        _coeff_elt_print(io, zero(T), first(basis(A)))
+        _coeff_elt_print(io, mime, zero(T), first(basis(A)))
     else
         _first = true
         for (idx, value) in nonzero_pairs(coeffs(a))
             c, elt = value, basis(A)[idx]
             if _first
-                _coeff_elt_print(io, c, elt)
+                _coeff_elt_print(io, mime, c, elt)
                 _first = false
             else
                 if __prints_with_minus(c)
                     print(io, ' ')
                 else
-                    print(io, ' ', '+')
+                    print(io, ' ', '+', ' ')
                 end
-                _coeff_elt_print(io, c, elt)
+                _coeff_elt_print(io, mime, c, elt)
             end
         end
     end