Make standalone prefix /> work. Improved lowering.

Author: c42f

src/expr.jl

@@ -303,25 +303,74 @@ function _to_expr(node::SyntaxNode; iteration_spec=false, need_linenodes=true,
             args[1] = Expr(headsym, args[1].args...)
             headsym = :const
         end
-    elseif headsym == Symbol("/>")
+    elseif headsym == Symbol("/>") || headsym == Symbol("\\>")
         freearg = gensym()
-        cargs = [args[1], freearg, args[2:end]...]
-        reorder_parameters!(cargs, 2)
-        return Expr(:->, freearg, Expr(:call, cargs...))
-    elseif headsym == Symbol("\\>")
-        freearg = gensym()
-        cargs = [args[1], args[2:end]..., freearg]
-        reorder_parameters!(cargs, 2)
-        return Expr(:->, freearg, Expr(:call, cargs...))
+        callex = only(args)
+        @assert Meta.isexpr(callex, :call)
+        args = callex.args
+        func = headsym == Symbol("/>") ?
+            :(JuliaSyntax.fixbutfirst) :
+            :(JuliaSyntax.fixbutlast)
+        if length(args) >= 2 && Meta.isexpr(args[2], :parameters)
+            return Expr(:call, func, args[2], args[1], args[3:end]...)
+        else
+            return Expr(:call, func, args...)
+        end
     elseif headsym == :chain
-        return Expr(:call, :(JuliaSyntax.chain), args...)
+        if kind(node_args[1]) in KSet"/> \>"
+            return Expr(:call, :(JuliaSyntax.compose_chain), args...)
+        else
+            return Expr(:call, :(JuliaSyntax.chain), args...)
+        end
     end
     return Expr(headsym, args...)
 end
 
+#-------------------------------------------------------------------------------
+# Targets for lowering /> and \> syntax
+
+# For use with />
+struct FixButFirst{F,Args,Kws}
+    f::F
+    args::Args
+    kwargs::Kws
+end
+
+(f::FixButFirst)(x) = f.f(x, f.args...; f.kwargs...)
+
+"""
+Fix all arguments except for the first
+"""
+fixbutfirst(f, args...; kws...) = FixButFirst(f, args, kws)
+
+# For use with \>
+struct FixButLast{F,Args,Kws}
+    f::F
+    args::Args
+    kwargs::Kws
+end
+
+(f::FixButLast)(x) = f.f(f.args..., x; f.kwargs...)
+
+"""
+Fix all arguments except for the last
+"""
+fixbutlast(f, args...; kws...) = FixButLast(f, args, kws)
+
 chain(x, f, fs...) = chain(f(x), fs...)
 chain(x) = x
 
+struct ComposeChain{Funcs}
+    fs::Funcs
+end
+
+(f::ComposeChain)(x) = chain(x, f.fs...)
+
+compose_chain(fs...) = ComposeChain(fs)
+
+
+#-------------------------------------------------------------------------------
+
 Base.Expr(node::SyntaxNode) = _to_expr(node)
 
 function build_tree(::Type{Expr}, stream::ParseStream; kws...)

src/parser.jl

@@ -800,20 +800,21 @@ end
 # x /> A.f(y)        ==>  (chain x (/> (. A (quote f)) y))
 function parse_curry_chain(ps::ParseState)
     mark = position(ps)
-    parse_range(ps)
-    has_chain = false
+    if (k = peek(ps); k != K"/>" && k != K"\>")
+        parse_range(ps)
+    end
+    chain_len = 0
     while (k = peek(ps); k == K"/>" || k == K"\>")
         bump(ps, TRIVIA_FLAG)
         m = position(ps)
         parse_range(ps)
-        if peek_behind(ps).kind == K"call"
-            has_chain = true
-            reset_node!(ps, position(ps), kind=k)
-        else
+        if peek_behind(ps).kind != K"call"
             emit(ps, m, K"error", error="Expected call to the right of />")
         end
+        emit(ps, m, k)
+        chain_len += 1
     end
-    if has_chain
+    if chain_len > 1
         emit(ps, mark, K"chain")
     end
 end